Europa’s carbon dioxide likely came from its ocean

This pixelated image is Jupiter’s moon Europa on November 9, 2022, from the Near Infrared Camera (NIRCam) on the James Webb Space Telescope. The white areas in the image correspond with the type of jumbled landscape known as chaos terrain. The white region at left (Powys Regio) and at center right (Tara Regio) are areas that have carbon dioxide ice on the surface. Two new studies show that Europa’s carbon dioxide likely originated in its subsurface ocean. The discovery has implications for the ability of life to survive there. Image via Science: NASA/ ESA/ CSA/ Gerónimo Villanueva (NASA-GSFC)/ Samantha K Trumbo (Cornell University); Image Processing: Gerónimo Villanueva (NASA-GSFC)/ Alyssa Pagan (STScI).

Jupiter’s moon Europa has a salty global ocean topped with a thick layer of ice. Now, astronomers have identified carbon dioxide on the moon’s icy surface and found that it’s a relatively recent deposit. On September 21, 2023, NASA announced two new studies that suggest the carbon dioxide came from deep in Europa’s ocean. If so, that could have significant implications for the habitability of the ocean, or even possible life itself. The studies used new data from NASA’s James Webb Space Telescope. The American Association for the Advancement of Science (AAAS) also reported the discovery via EurekAlert!.

The researchers published the two new peer-reviewed papers on September 21 in the journal Science. Read the 1st paper here and the 2nd paper here.

Where did Europa’s carbon dioxide come from?

So how did the carbon dioxide on Europa’s surface get there? Did it originate directly from the ocean below or did meteorites deliver it to Europa? Or could Jupiter’s magnetosphere interacting with chemicals on the surface have produced it?

Scientists want to know the source because it can tell them a lot about what conditions are like in the ocean. Whether the carbon dioxide originated in the ocean or not can make a big difference in terms of chemistry and potential habitability.

Carbon is most likely from Europa’s ocean

Both of the studies used recent data from NASA’s James Webb Space Telescope. Webb analyzed the moon’s surface in near-infrared wavelengths. It mapped out the distribution of carbon dioxide ice and found that the highest concentration was in Tara Regio. That region is about 695 square miles (1,800 square km) and is dominated by what scientists call chaos terrain. In chaos terrain, surface materials show geological disruption and resurfacing. And there’s an exchange of material between the subsurface ocean and the icy surface. It’s some of the youngest terrain on Europa’s surface.

The analysis results suggest that the enriched levels of carbon dioxide in Tara Regio may mean that the carbon originated in Europa’s ocean. This is the endogenous scenario, where the carbon came from within Europa. The researchers said that the carbon came to the surface relatively recently on a geological timescale. In addition, this is also supported by the fact that carbon is unstable on Europa’s surface. So any deposits must be geologically young.

Samantha Trumbo of Cornell University, lead author of the 2nd paper, stated:

Previous observations from the Hubble Space Telescope show evidence for ocean-derived salt in Tara Regio. Now we’re seeing that carbon dioxide is heavily concentrated there as well. We think this implies that the carbon probably has its ultimate origin in the internal ocean.

Other carbonates or organics as a source

The researchers added, however, that it is still possible the formation of the carbon dioxide occurred on the surface itself, from carbonates or other organics. The 1st paper said:

A second potential source of CO2 could be carbonate-bearing fluids (e.g., sodium bicarbonate dissolved in water). Enceladus has a carbonate-rich ocean that degases CO2; some of that degassed CO2 freezes out on the surface. A similar process could occur on Europa.

A third possibility is that the carbon might be from organic compounds that were originally dissolved or suspended in a subsurface liquid-water reservoir, which were later converted to CO2. CO2 might be generated by irradiation on the surface, when material sourced from Europa’s interior, rich in carbonate salts and/or organics mixed with H2O, is bombarded by charged particles trapped in Jupiter’s magnetosphere.

View larger. | This graphic shows a map of Europa’s surface with its Near Infrared Camera (NIRCam) on NASA’s James Webb Space Telescope in the 1st panel. The other 3 panels are compositional maps derived from Webb’s Near Infrared Spectrograph (NIRSpec) data. In the compositional maps, the white pixels correspond to carbon dioxide in Tara Regio (center and right), with additional concentrations within portions of the chaos region Powys Regio (left). The 2nd and 3rd panels show evidence of crystalline carbon dioxide, while the 4th panel indicates a complex and amorphous form of carbon dioxide. Image via Science: NASA/ ESA/ CSA/ Gerónimo Villanueva (NASA-GSFC)/ Samantha K Trumbo (Cornell University); Image Processing: Gerónimo Villanueva (NASA-GSFC)/ Alyssa Pagan (STScI).

External source of Europa’s carbon dioxide is unlikely

Significantly, the studies cast doubt on an exogenous – external – source of the carbon dioxide, such as meteorites. As the 1st paper notes:

Exogenous explanations for the observed CO2 on Europa are possible, but an exogenous source would likely produce a more global distribution, not the observed local concentration that is associated with salts (which are presumably endogenous). CO2 ice is also localized on Enceladus, where it is known to be endogenous. Exogenous interplanetary dust grains might deliver carbonaceous material to Europa’s icy surface, which could then yield CO2 through radiolysis, but no silicate features indicative of such exogenous material have been reported for Europa. Given the CO2 association with NaCl, and our laboratory results, we conclude that the most likely origin of the observed CO2 is endogenous, at least within Tara Regio.

Life in Europa’s ocean?

There is also, of course, the question of what originally produced the carbon dioxide if it does come from the ocean. Could it possibly be biological? Indeed, carbon is essential for life as we know it, and all life on Earth is carbon-based.

Unfortunately, as discussed in the 2nd paper, the researchers did analyze the isotopic ratio but couldn’t determine whether or not it was associated with life. But carbon in the ocean is still an encouraging sign for the possibility of life. Lead author of the first paper, Geronimo Villanueva of NASA’s Goddard Space Flight Center, said:

On Earth, life likes chemical diversity; the more diversity, the better. We’re carbon-based life. Understanding the chemistry of Europa’s ocean will help us determine whether it’s hostile to life as we know it, or if it might be a good place for life.

Trumbo added:

We now think that we have observational evidence that the carbon we see on Europa’s surface came from the ocean. That’s not a trivial thing. Carbon is a biologically essential element.

Previous studies have also supported the possibility that this alien ocean is habitable, by earthly standards.

View larger. | NASA’s Galileo spacecraft captured this view of Europa’s cracked, icy surface in the 1990s. It combines images from 1995 and 1998. Image via NASA/ JPL-Caltech/ SETI Institute.

No water plumes in new search

The researchers also looked for signs of Europa’s tentative water vapor plumes in the Webb data but didn’t see any. As has been surmised before, the plumes may be infrequent and smaller than those on Saturn’s moon Enceladus. It’s also possible that the plumes didn’t contain the volatile gases that the researchers included in their search. Heidi Hammel of the Association of Universities for Research in Astronomy (AURA) said:

There is always a possibility that these plumes are variable and that you can only see them at certain times. All we can say with 100% confidence is that we did not detect a plume at Europa when we made these observations with Webb.

The new results are not only exciting, but they also show how powerful and efficient Webb is. It only took Webb a few minutes to conduct these observations, as Hammel noted:

These observations only took a few minutes of the observatory’s time. Even with this short period of time, we were able to do really big science. This work gives a first hint of all the amazing solar system science we’ll be able to do with Webb.

Bottom line: Two new studies suggest that Europa’s carbon dioxide deposits originate in the moon’s subsurface ocean. The results support a habitable ocean environment.

Source: Endogenous CO2 ice mixture on the surface of Europa and no detection of plume activity

Source: The distribution of CO2 on Europa indicates an internal source of carbon

Via Webb Space Telescope

Via EurekAlert!

Read more: Do Europa’s odd ridges indicate life?

The post Europa’s carbon dioxide likely came from its ocean first appeared on EarthSky.

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This pixelated image is Jupiter’s moon Europa on November 9, 2022, from the Near Infrared Camera (NIRCam) on the James Webb Space Telescope. The white areas in the image correspond with the type of jumbled landscape known as chaos terrain. The white region at left (Powys Regio) and at center right (Tara Regio) are areas that have carbon dioxide ice on the surface. Two new studies show that Europa’s carbon dioxide likely originated in its subsurface ocean. The discovery has implications for the ability of life to survive there. Image via Science: NASA/ ESA/ CSA/ Gerónimo Villanueva (NASA-GSFC)/ Samantha K Trumbo (Cornell University); Image Processing: Gerónimo Villanueva (NASA-GSFC)/ Alyssa Pagan (STScI).

Jupiter’s moon Europa has a salty global ocean topped with a thick layer of ice. Now, astronomers have identified carbon dioxide on the moon’s icy surface and found that it’s a relatively recent deposit. On September 21, 2023, NASA announced two new studies that suggest the carbon dioxide came from deep in Europa’s ocean. If so, that could have significant implications for the habitability of the ocean, or even possible life itself. The studies used new data from NASA’s James Webb Space Telescope. The American Association for the Advancement of Science (AAAS) also reported the discovery via EurekAlert!.

The researchers published the two new peer-reviewed papers on September 21 in the journal Science. Read the 1st paper here and the 2nd paper here.

Where did Europa’s carbon dioxide come from?

So how did the carbon dioxide on Europa’s surface get there? Did it originate directly from the ocean below or did meteorites deliver it to Europa? Or could Jupiter’s magnetosphere interacting with chemicals on the surface have produced it?

Scientists want to know the source because it can tell them a lot about what conditions are like in the ocean. Whether the carbon dioxide originated in the ocean or not can make a big difference in terms of chemistry and potential habitability.

Carbon is most likely from Europa’s ocean

Both of the studies used recent data from NASA’s James Webb Space Telescope. Webb analyzed the moon’s surface in near-infrared wavelengths. It mapped out the distribution of carbon dioxide ice and found that the highest concentration was in Tara Regio. That region is about 695 square miles (1,800 square km) and is dominated by what scientists call chaos terrain. In chaos terrain, surface materials show geological disruption and resurfacing. And there’s an exchange of material between the subsurface ocean and the icy surface. It’s some of the youngest terrain on Europa’s surface.

The analysis results suggest that the enriched levels of carbon dioxide in Tara Regio may mean that the carbon originated in Europa’s ocean. This is the endogenous scenario, where the carbon came from within Europa. The researchers said that the carbon came to the surface relatively recently on a geological timescale. In addition, this is also supported by the fact that carbon is unstable on Europa’s surface. So any deposits must be geologically young.

Samantha Trumbo of Cornell University, lead author of the 2nd paper, stated:

Previous observations from the Hubble Space Telescope show evidence for ocean-derived salt in Tara Regio. Now we’re seeing that carbon dioxide is heavily concentrated there as well. We think this implies that the carbon probably has its ultimate origin in the internal ocean.

Other carbonates or organics as a source

The researchers added, however, that it is still possible the formation of the carbon dioxide occurred on the surface itself, from carbonates or other organics. The 1st paper said:

A second potential source of CO2 could be carbonate-bearing fluids (e.g., sodium bicarbonate dissolved in water). Enceladus has a carbonate-rich ocean that degases CO2; some of that degassed CO2 freezes out on the surface. A similar process could occur on Europa.

A third possibility is that the carbon might be from organic compounds that were originally dissolved or suspended in a subsurface liquid-water reservoir, which were later converted to CO2. CO2 might be generated by irradiation on the surface, when material sourced from Europa’s interior, rich in carbonate salts and/or organics mixed with H2O, is bombarded by charged particles trapped in Jupiter’s magnetosphere.

View larger. | This graphic shows a map of Europa’s surface with its Near Infrared Camera (NIRCam) on NASA’s James Webb Space Telescope in the 1st panel. The other 3 panels are compositional maps derived from Webb’s Near Infrared Spectrograph (NIRSpec) data. In the compositional maps, the white pixels correspond to carbon dioxide in Tara Regio (center and right), with additional concentrations within portions of the chaos region Powys Regio (left). The 2nd and 3rd panels show evidence of crystalline carbon dioxide, while the 4th panel indicates a complex and amorphous form of carbon dioxide. Image via Science: NASA/ ESA/ CSA/ Gerónimo Villanueva (NASA-GSFC)/ Samantha K Trumbo (Cornell University); Image Processing: Gerónimo Villanueva (NASA-GSFC)/ Alyssa Pagan (STScI).

External source of Europa’s carbon dioxide is unlikely

Significantly, the studies cast doubt on an exogenous – external – source of the carbon dioxide, such as meteorites. As the 1st paper notes:

Exogenous explanations for the observed CO2 on Europa are possible, but an exogenous source would likely produce a more global distribution, not the observed local concentration that is associated with salts (which are presumably endogenous). CO2 ice is also localized on Enceladus, where it is known to be endogenous. Exogenous interplanetary dust grains might deliver carbonaceous material to Europa’s icy surface, which could then yield CO2 through radiolysis, but no silicate features indicative of such exogenous material have been reported for Europa. Given the CO2 association with NaCl, and our laboratory results, we conclude that the most likely origin of the observed CO2 is endogenous, at least within Tara Regio.

Life in Europa’s ocean?

There is also, of course, the question of what originally produced the carbon dioxide if it does come from the ocean. Could it possibly be biological? Indeed, carbon is essential for life as we know it, and all life on Earth is carbon-based.

Unfortunately, as discussed in the 2nd paper, the researchers did analyze the isotopic ratio but couldn’t determine whether or not it was associated with life. But carbon in the ocean is still an encouraging sign for the possibility of life. Lead author of the first paper, Geronimo Villanueva of NASA’s Goddard Space Flight Center, said:

On Earth, life likes chemical diversity; the more diversity, the better. We’re carbon-based life. Understanding the chemistry of Europa’s ocean will help us determine whether it’s hostile to life as we know it, or if it might be a good place for life.

Trumbo added:

We now think that we have observational evidence that the carbon we see on Europa’s surface came from the ocean. That’s not a trivial thing. Carbon is a biologically essential element.

Previous studies have also supported the possibility that this alien ocean is habitable, by earthly standards.

View larger. | NASA’s Galileo spacecraft captured this view of Europa’s cracked, icy surface in the 1990s. It combines images from 1995 and 1998. Image via NASA/ JPL-Caltech/ SETI Institute.

No water plumes in new search

The researchers also looked for signs of Europa’s tentative water vapor plumes in the Webb data but didn’t see any. As has been surmised before, the plumes may be infrequent and smaller than those on Saturn’s moon Enceladus. It’s also possible that the plumes didn’t contain the volatile gases that the researchers included in their search. Heidi Hammel of the Association of Universities for Research in Astronomy (AURA) said:

There is always a possibility that these plumes are variable and that you can only see them at certain times. All we can say with 100% confidence is that we did not detect a plume at Europa when we made these observations with Webb.

The new results are not only exciting, but they also show how powerful and efficient Webb is. It only took Webb a few minutes to conduct these observations, as Hammel noted:

These observations only took a few minutes of the observatory’s time. Even with this short period of time, we were able to do really big science. This work gives a first hint of all the amazing solar system science we’ll be able to do with Webb.

Bottom line: Two new studies suggest that Europa’s carbon dioxide deposits originate in the moon’s subsurface ocean. The results support a habitable ocean environment.

Source: Endogenous CO2 ice mixture on the surface of Europa and no detection of plume activity

Source: The distribution of CO2 on Europa indicates an internal source of carbon

Via Webb Space Telescope

Via EurekAlert!

Read more: Do Europa’s odd ridges indicate life?

The post Europa’s carbon dioxide likely came from its ocean first appeared on EarthSky.

from EarthSky https://ift.tt/lL0qWtQ

Pablo Neruda, a poet who embraced cosmic beauty

View larger. | Image composed with Photoshop via Michael West. Poem by Pablo Neruda.

Playing with the light of the universe

The great Chilean poet Pablo Neruda (1904-1973) died 50 years ago today, on September 23, 1973. Some years ago, astronomer Michael West of Lowell Observatory in Flagstaff, Arizona, shared the image above with us. It’s a photo he took inscribed with Neruda’s words. West wrote:

Astronomical imagery often figured in Neruda’s poetry, for example, one of his poems begins: Every day you play with the light of the universe.

Another poem titled The Future is Space describes black space with room for many dreams.

In the attached composite image (made from photos I took in Chile) I’ve included a portion of Neruda’s poem titled La Poesía in which the Nobel Prize winner described the feeling of discovering poetry as a youth, comparing it to the beauty of the universe.

… As you know, Neruda’s homeland of Chile, which he loved, is now home to many of the world’s greatest telescopes, including the future European Southern Observatory Extremely Large Telescope (ELT) and the Giant Magellan Telescope (GMT).

Original photo taken with a Canon 5D MkIII.

Post-processing via Photoshop CC + Nik plug-ins.

Thank you for sharing your image with Neruda’s words, Michael!

Pablo Neruda’s life

Pablo Neruda as a young man. Read more about him. Image via Wikipedia (public domain).

Pablo Neruda was born Ricardo Eliécer Neftalí Reyes Basoalto on July 12, 1904. And he began writing poems at the age of 13, and later became a poet-diplomat and politician who won the Nobel Prize for Literature in 1971. In fact, the space imagery in his poems inspired scientists to name a crater on Mercury in his honor. Neruda Crater is 70 miles (112 km) across.

The Johns Hopkins Applied Physics Laboratory website describes Neruda Crater as follows:

The crater exhibits several central peaks punctuated by a more recent, small crater, resulting in a rugged profile of ups and downs if one were to traverse the crater floor. Similarly, the crater’s namesake Neruda experienced a number of ups and downs in his life, from success as a poet, through poverty, war and ultimately alleged poisoning.

An exhumation and studies of Neruda’s remains from 2013 to 2017 found that Neruda had prostate cancer and may have had a staph infection at the time of his death. His manner of death is listed as a heart attack, and foul play has never been proven.

MESSENGER, a spacecraft that visited Mercury, took this image of the Neruda Crater, named for Chilean poet Pablo Neruda, on July 24, 2012. Image via NASA/ Wikipedia (public domain).

Bottom line: On September 23, 1973, the great Chilean poet, Pablo Neruda, passed away. Fifty years later, we honor his connection to astronomy.

The post Pablo Neruda, a poet who embraced cosmic beauty first appeared on EarthSky.

from EarthSky https://ift.tt/Nxz3jUD

View larger. | Image composed with Photoshop via Michael West. Poem by Pablo Neruda.

Playing with the light of the universe

The great Chilean poet Pablo Neruda (1904-1973) died 50 years ago today, on September 23, 1973. Some years ago, astronomer Michael West of Lowell Observatory in Flagstaff, Arizona, shared the image above with us. It’s a photo he took inscribed with Neruda’s words. West wrote:

Astronomical imagery often figured in Neruda’s poetry, for example, one of his poems begins: Every day you play with the light of the universe.

Another poem titled The Future is Space describes black space with room for many dreams.

In the attached composite image (made from photos I took in Chile) I’ve included a portion of Neruda’s poem titled La Poesía in which the Nobel Prize winner described the feeling of discovering poetry as a youth, comparing it to the beauty of the universe.

… As you know, Neruda’s homeland of Chile, which he loved, is now home to many of the world’s greatest telescopes, including the future European Southern Observatory Extremely Large Telescope (ELT) and the Giant Magellan Telescope (GMT).

Original photo taken with a Canon 5D MkIII.

Post-processing via Photoshop CC + Nik plug-ins.

Thank you for sharing your image with Neruda’s words, Michael!

Pablo Neruda’s life

Pablo Neruda as a young man. Read more about him. Image via Wikipedia (public domain).

Pablo Neruda was born Ricardo Eliécer Neftalí Reyes Basoalto on July 12, 1904. And he began writing poems at the age of 13, and later became a poet-diplomat and politician who won the Nobel Prize for Literature in 1971. In fact, the space imagery in his poems inspired scientists to name a crater on Mercury in his honor. Neruda Crater is 70 miles (112 km) across.

The Johns Hopkins Applied Physics Laboratory website describes Neruda Crater as follows:

The crater exhibits several central peaks punctuated by a more recent, small crater, resulting in a rugged profile of ups and downs if one were to traverse the crater floor. Similarly, the crater’s namesake Neruda experienced a number of ups and downs in his life, from success as a poet, through poverty, war and ultimately alleged poisoning.

An exhumation and studies of Neruda’s remains from 2013 to 2017 found that Neruda had prostate cancer and may have had a staph infection at the time of his death. His manner of death is listed as a heart attack, and foul play has never been proven.

MESSENGER, a spacecraft that visited Mercury, took this image of the Neruda Crater, named for Chilean poet Pablo Neruda, on July 24, 2012. Image via NASA/ Wikipedia (public domain).

Bottom line: On September 23, 1973, the great Chilean poet, Pablo Neruda, passed away. Fifty years later, we honor his connection to astronomy.

The post Pablo Neruda, a poet who embraced cosmic beauty first appeared on EarthSky.

from EarthSky https://ift.tt/Nxz3jUD

Why does Earth have 4 seasons every year?

View at EarthSky Community Photos. | Sharon Kizer, who is mother to EarthSky’s Kelly Kizer Whitt, took this image of fiery maples and rain clouds on October 9, 2022, in Madison, Wisconsin. It illustrates some of the vivid reds of autumn. Thank you, Sharon! But why does Earth have 4 seasons every year? Read more below.

Tomorrow’s September equinox signals the change of season, from summer to fall in the Northern Hemisphere and from winter to spring in the Southern Hemisphere. But why do Earth’s seasons change?

The 4 seasons come from Earth’s tilt

Some assume our planet’s changing distance from the sun causes the change in the seasons. It’s logical, but not the case for Earth. Instead, Earth has seasons because our planet’s axis of rotation is tilted at an angle of 23.5 degrees relative to our orbital plane, that is, the plane of Earth’s orbit around the sun.

The tilt in the axis of the Earth is called its obliquity by scientists.

Obliquity. Image via Wikipedia.

Over the course of a year, the angle of tilt does not vary. In other words, Earth’s northern axis is always pointing the same direction in space. At this time, that direction is more or less toward the star we call Polaris, the North Star.

If Earth did not tilt at all, but instead orbited exactly upright with respect to our orbit around the sun, there would be minor variations in temperature throughout each year as Earth moved slightly closer to the sun and then slightly farther away. But, without Earth’s tilt, we’d lack Earth’s wonderful seasonal changes and our association of them with the various times of year. For example, associating a crisp feeling in the air with autumn.

But wait, there’s more

However, the orientation of Earth’s tilt with respect to the sun – our source of light and warmth – does change as we orbit the sun. In other words, the Northern Hemisphere is oriented toward the sun for half of the year and away from the sun for the other half. The same is true of the Southern Hemisphere.

The fact is, our seasons result from the Earth’s rotational axis tilting 23.5 degrees out of the perpendicular to the ecliptic, or Earth’s orbital plane. So at different times of the year, different parts of the globe receive more direct sunlight. Image via weather.gov.

When the Northern Hemisphere is oriented toward the sun, that region of Earth warms because of the corresponding increase in solar radiation. The sun’s rays are striking that part of Earth at a more direct angle. It’s summer.

When the Northern Hemisphere is oriented away from the sun, the sun’s rays are less direct. Hence, that part of Earth cools. It’s winter.

Seasons in the Southern Hemisphere occur at opposite times of the year from those in the Northern Hemisphere. Northern summer = southern winter.

Why does Earth’s axis tilt?

View at EarthSky Community Photos. | Elmarie van Rooyen captured this snowy scene at Smoky Lake, Alberta, Canada, on December 31, 2022, and wrote: “It was one of the most beautiful days yesterday before saying goodbye to 2022.” Thank you, Elmarie!

The tilt in Earth’s axis is strongly influenced by the way mass is distributed over the planet. Large amounts of land mass and ice sheets in the Northern Hemisphere make Earth top-heavy. An analogy for obliquity is imagining what would happen if you were to spin a ball with a big piece of bubble gum stuck near the top. The extra weight would cause the ball to tilt when spun.

Over long periods of geological time, the angle of Earth’s obliquity cycles between 21.1 and 24.5 degrees. This cycle lasts approximately 41,000 years. And it may play a key role in the formation of ice ages – a scientific theory proposed by Milutin Milankovitch in 1930.

The Earth is currently decreasing in obliquity. Decreases in obliquity can set the stage for more moderate seasons (cooler summers and warmer winters). On the other hand, increases in obliquity create more extreme seasons (hotter summers and colder winters). Glaciers tend to grow when the Earth has many cool summers that fail to melt back the winter snows. Remember, we’re talking about a 41,000-year cycle here, so these changes in obliquity are not the primary driver of Earth’s climate. Temperatures on Earth are influenced not just by obliquity. Many other factors contribute to our complex climate system and the global temperatures we experience from year to year. 

All the planets in the solar system tilt on their axis

Other planets in our solar system also tilt at various degrees. Uranus rotates almost sideways at 97 degrees and has extreme seasons. The axial tilt on Venus is 177.3 degrees. Hence, Venus has very little in the way of seasons.

Earth’s distance from the sun does change throughout the year. So it’s logical to assume that an increase or decrease in any sun-planet distance could cause a cyclical change in the seasons. But – at least in the case of our planet – this change is too small to cause seasonal changes.

However, some extrasolar planets – planets orbiting distant stars – have been found with more extreme orbits. And even in our own solar system, for example, the planet Mars has a more elliptical orbit than Earth does. Its distance from the sun changes more dramatically through its year than Earth’s does. And the change in Mars’ distance from the sun does cause some more pronounced cyclical changes on this red desert world.

The hottest days occur after the summer solstice and it’s a lovely time to spend on the beach. Image via Quang Nguyen Vinh / pexels.com. Used with permission.

Bottom line: It’s logical to assume our planet’s changing distance from the sun causes the change in the seasons. But Earth’s distance from the sun doesn’t change enough to cause seasonal differences. Instead, our seasons change because Earth tilts on its axis, and the angle of tilt causes the Northern and Southern Hemispheres to trade places throughout the year in receiving the sun’s light and warmth most directly.

The post Why does Earth have 4 seasons every year? first appeared on EarthSky.

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View at EarthSky Community Photos. | Sharon Kizer, who is mother to EarthSky’s Kelly Kizer Whitt, took this image of fiery maples and rain clouds on October 9, 2022, in Madison, Wisconsin. It illustrates some of the vivid reds of autumn. Thank you, Sharon! But why does Earth have 4 seasons every year? Read more below.

Tomorrow’s September equinox signals the change of season, from summer to fall in the Northern Hemisphere and from winter to spring in the Southern Hemisphere. But why do Earth’s seasons change?

The 4 seasons come from Earth’s tilt

Some assume our planet’s changing distance from the sun causes the change in the seasons. It’s logical, but not the case for Earth. Instead, Earth has seasons because our planet’s axis of rotation is tilted at an angle of 23.5 degrees relative to our orbital plane, that is, the plane of Earth’s orbit around the sun.

The tilt in the axis of the Earth is called its obliquity by scientists.

Obliquity. Image via Wikipedia.

Over the course of a year, the angle of tilt does not vary. In other words, Earth’s northern axis is always pointing the same direction in space. At this time, that direction is more or less toward the star we call Polaris, the North Star.

If Earth did not tilt at all, but instead orbited exactly upright with respect to our orbit around the sun, there would be minor variations in temperature throughout each year as Earth moved slightly closer to the sun and then slightly farther away. But, without Earth’s tilt, we’d lack Earth’s wonderful seasonal changes and our association of them with the various times of year. For example, associating a crisp feeling in the air with autumn.

But wait, there’s more

However, the orientation of Earth’s tilt with respect to the sun – our source of light and warmth – does change as we orbit the sun. In other words, the Northern Hemisphere is oriented toward the sun for half of the year and away from the sun for the other half. The same is true of the Southern Hemisphere.

The fact is, our seasons result from the Earth’s rotational axis tilting 23.5 degrees out of the perpendicular to the ecliptic, or Earth’s orbital plane. So at different times of the year, different parts of the globe receive more direct sunlight. Image via weather.gov.

When the Northern Hemisphere is oriented toward the sun, that region of Earth warms because of the corresponding increase in solar radiation. The sun’s rays are striking that part of Earth at a more direct angle. It’s summer.

When the Northern Hemisphere is oriented away from the sun, the sun’s rays are less direct. Hence, that part of Earth cools. It’s winter.

Seasons in the Southern Hemisphere occur at opposite times of the year from those in the Northern Hemisphere. Northern summer = southern winter.

Why does Earth’s axis tilt?

View at EarthSky Community Photos. | Elmarie van Rooyen captured this snowy scene at Smoky Lake, Alberta, Canada, on December 31, 2022, and wrote: “It was one of the most beautiful days yesterday before saying goodbye to 2022.” Thank you, Elmarie!

The tilt in Earth’s axis is strongly influenced by the way mass is distributed over the planet. Large amounts of land mass and ice sheets in the Northern Hemisphere make Earth top-heavy. An analogy for obliquity is imagining what would happen if you were to spin a ball with a big piece of bubble gum stuck near the top. The extra weight would cause the ball to tilt when spun.

Over long periods of geological time, the angle of Earth’s obliquity cycles between 21.1 and 24.5 degrees. This cycle lasts approximately 41,000 years. And it may play a key role in the formation of ice ages – a scientific theory proposed by Milutin Milankovitch in 1930.

The Earth is currently decreasing in obliquity. Decreases in obliquity can set the stage for more moderate seasons (cooler summers and warmer winters). On the other hand, increases in obliquity create more extreme seasons (hotter summers and colder winters). Glaciers tend to grow when the Earth has many cool summers that fail to melt back the winter snows. Remember, we’re talking about a 41,000-year cycle here, so these changes in obliquity are not the primary driver of Earth’s climate. Temperatures on Earth are influenced not just by obliquity. Many other factors contribute to our complex climate system and the global temperatures we experience from year to year. 

All the planets in the solar system tilt on their axis

Other planets in our solar system also tilt at various degrees. Uranus rotates almost sideways at 97 degrees and has extreme seasons. The axial tilt on Venus is 177.3 degrees. Hence, Venus has very little in the way of seasons.

Earth’s distance from the sun does change throughout the year. So it’s logical to assume that an increase or decrease in any sun-planet distance could cause a cyclical change in the seasons. But – at least in the case of our planet – this change is too small to cause seasonal changes.

However, some extrasolar planets – planets orbiting distant stars – have been found with more extreme orbits. And even in our own solar system, for example, the planet Mars has a more elliptical orbit than Earth does. Its distance from the sun changes more dramatically through its year than Earth’s does. And the change in Mars’ distance from the sun does cause some more pronounced cyclical changes on this red desert world.

The hottest days occur after the summer solstice and it’s a lovely time to spend on the beach. Image via Quang Nguyen Vinh / pexels.com. Used with permission.

Bottom line: It’s logical to assume our planet’s changing distance from the sun causes the change in the seasons. But Earth’s distance from the sun doesn’t change enough to cause seasonal differences. Instead, our seasons change because Earth tilts on its axis, and the angle of tilt causes the Northern and Southern Hemispheres to trade places throughout the year in receiving the sun’s light and warmth most directly.

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On the equinox, are day and night equal?

Flattened sunset by Helio C. Vital in Rio de Janeiro, Brazil. A flattened sunset is an effect of atmospheric refraction. Refraction also gives us a few more minutes of daylight on the equinox than we would have otherwise.

The September equinox happens at 6:50 UTC (1:50 a.m. CDT) on September 23, 2023.

Are day and night equal on the equinox?

Twice a year – on the March and September equinoxes – everyone worldwide supposedly receives exactly 12 hours of day and exactly 12 hours of night. But that’s not precisely true. In fact, there’s about eight more minutes of daylight – at mid-temperate latitudes – on the day of an equinox. And there are two reasons why. They are:

1. The sun is a disk, not a point.

2. Atmospheric refraction.

Keep reading to learn more …

The sun is a disk, not a point

Watch any sunset, and you know the sun appears in Earth’s sky as a disk.

It’s not pointlike, as stars are, and yet – by definition – most almanacs regard sunrise as when the leading edge of the sun first touches the eastern horizon. They define sunset as when the sun’s trailing edge finally touches the western horizon.

This alone provides an extra 2 1/2 to 3 minutes of daylight at mid-temperate latitudes.

Atmospheric refraction raises the sun about 1/2 degree upward in our sky at both sunrise and sunset. This advances the time of actual sunrise, while delaying the time of actual sunset. The result is several minutes of extra daylight, not just at an equinox, but every day. Image via Wikipedia.

Atmospheric refraction and the equinox

The Earth’s atmosphere acts like a lens or prism, uplifting the sun about half a degree from its true geometrical position whenever the sun nears the horizon. Coincidentally, the sun’s angular diameter spans about half a degree, as well.

In other words, when you see the sun on the horizon, it’s actually just below the horizon geometrically.

What does atmospheric refraction mean for the length of daylight? It advances the sunrise and delays the sunset, adding nearly another six minutes of daylight at mid-temperate latitudes. Hence, more daylight than night at the equinox.

Astronomical almanacs usually don’t give sunrise or sunset times to the second. That’s because atmospheric refraction varies somewhat, depending on air temperature, humidity and barometric pressure. Lower temperature, higher humidity and higher barometric pressure all increase atmospheric refraction.

On the day of the equinox, the center of the sun would set about 12 hours after rising, given a level horizon, as at sea, and no atmospheric refraction.

What is an equilux?

Here’s a new word for you: equilux. The word is used to describe the day on which day and night are equal. The equilux happens a few to several days after the autumn equinox, and a few to several days before the spring equinox.

Much as earliest sunrises and latest sunsets vary with latitude, so the exact date of an equilux varies with latitude. That’s in contrast to the equinox itself, which is a whole-Earth event, happening at the same instant worldwide. At and near the equator, there is no equilux whatsoever, because the daylight period is over 12 hours long every day of the year.

Illustrations like this one make it seem as if day and night should be equal at the equinox. In fact, they aren’t exactly equal. Image via Wikimedia Commons.

Visit timeanddate.com for the approximate date of equal day and night at your latitude

Bottom line: There’s slightly more day than night on the day of an equinox. That’s because the sun is a disk, not a point of light, and because Earth’s atmosphere refracts (bends) sunlight.

Read more about the September 2023 equinox: All you need to know

The post On the equinox, are day and night equal? first appeared on EarthSky.

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Flattened sunset by Helio C. Vital in Rio de Janeiro, Brazil. A flattened sunset is an effect of atmospheric refraction. Refraction also gives us a few more minutes of daylight on the equinox than we would have otherwise.

The September equinox happens at 6:50 UTC (1:50 a.m. CDT) on September 23, 2023.

Are day and night equal on the equinox?

Twice a year – on the March and September equinoxes – everyone worldwide supposedly receives exactly 12 hours of day and exactly 12 hours of night. But that’s not precisely true. In fact, there’s about eight more minutes of daylight – at mid-temperate latitudes – on the day of an equinox. And there are two reasons why. They are:

1. The sun is a disk, not a point.

2. Atmospheric refraction.

Keep reading to learn more …

The sun is a disk, not a point

Watch any sunset, and you know the sun appears in Earth’s sky as a disk.

It’s not pointlike, as stars are, and yet – by definition – most almanacs regard sunrise as when the leading edge of the sun first touches the eastern horizon. They define sunset as when the sun’s trailing edge finally touches the western horizon.

This alone provides an extra 2 1/2 to 3 minutes of daylight at mid-temperate latitudes.

Atmospheric refraction raises the sun about 1/2 degree upward in our sky at both sunrise and sunset. This advances the time of actual sunrise, while delaying the time of actual sunset. The result is several minutes of extra daylight, not just at an equinox, but every day. Image via Wikipedia.

Atmospheric refraction and the equinox

The Earth’s atmosphere acts like a lens or prism, uplifting the sun about half a degree from its true geometrical position whenever the sun nears the horizon. Coincidentally, the sun’s angular diameter spans about half a degree, as well.

In other words, when you see the sun on the horizon, it’s actually just below the horizon geometrically.

What does atmospheric refraction mean for the length of daylight? It advances the sunrise and delays the sunset, adding nearly another six minutes of daylight at mid-temperate latitudes. Hence, more daylight than night at the equinox.

Astronomical almanacs usually don’t give sunrise or sunset times to the second. That’s because atmospheric refraction varies somewhat, depending on air temperature, humidity and barometric pressure. Lower temperature, higher humidity and higher barometric pressure all increase atmospheric refraction.

On the day of the equinox, the center of the sun would set about 12 hours after rising, given a level horizon, as at sea, and no atmospheric refraction.

What is an equilux?

Here’s a new word for you: equilux. The word is used to describe the day on which day and night are equal. The equilux happens a few to several days after the autumn equinox, and a few to several days before the spring equinox.

Much as earliest sunrises and latest sunsets vary with latitude, so the exact date of an equilux varies with latitude. That’s in contrast to the equinox itself, which is a whole-Earth event, happening at the same instant worldwide. At and near the equator, there is no equilux whatsoever, because the daylight period is over 12 hours long every day of the year.

Illustrations like this one make it seem as if day and night should be equal at the equinox. In fact, they aren’t exactly equal. Image via Wikimedia Commons.

Visit timeanddate.com for the approximate date of equal day and night at your latitude

Bottom line: There’s slightly more day than night on the day of an equinox. That’s because the sun is a disk, not a point of light, and because Earth’s atmosphere refracts (bends) sunlight.

Read more about the September 2023 equinox: All you need to know

The post On the equinox, are day and night equal? first appeared on EarthSky.

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Florida’s bleached corals get emergency sunshades

Three scuba divers install shade structures over some bleached corals in Biscayne National Park in Florida on August 18, 2023. The summer of 2023 brought a perilous heatwave to the ocean. The corals here are attached to cement blocks as part of a USGS experiment that provides data on corals throughout the western Atlantic. The shade structures could help reduce light stress on the bleached corals. Image via USGS.

Some bleached corals get emergency relief

Coral reefs around the world are in peril from a number of causes. Oil spills, pollution, storms and increasing temperatures can all endanger corals. The summer of 2023 brought some of the highest sea surface temperatures on record. As more and more corals bleached under the ocean heatwave, some scientists sought to provide shelter for the corals in the form of sunshades.

Erecting sunshades in the Dry Tortugas

On August 13, 2023, three scientists from the St. Petersburg Coastal and Marine Science Center went on a mission to protect endangered corals. The scientists donned wetsuits and scuba gear and entered the waters of Dry Tortugas National Park. There, they found the heat already affecting many of the corals.

The heat drained, or bleached, the corals of their color. Coral can survive bleaching, but they are more stressed and likely to die. Bleaching happens when water temperatures reach 87 F (30 C). In Florida this summer, the sea surface temperatures not only hit 87 F, they hit the 90s for extended periods of time, even cracking the 100-degree mark. And it wasn’t just Florida that had high sea surface temperatures, but many places around the globe.

The scientists constructed nearly 40 temporary sunshades over corals in the Dry Tortugas. How would an underwater sunshade help? Ilsa Kuffner, a USGS research marine biologist who participated in the emergency procedure, said:

The shading helps by reducing the sun’s rays. While normally corals need sunlight for their symbionts to photosynthesize, when they are bleached, the sun’s energy instead causes a lot of stress.

The sunshades weren’t the only measure the scientists used in their attempts to save the coral. In addition to the sunshades, the team also spent several evenings adding dim lights to the shaded coral in an effort to attract prey for the coral to feed on.

Other corals also got sunshades

After working in the Dry Tortugas, the scientists went to work in Biscayne National Park. With the help of two more scientists, they erected sunshades there as well. Kuffner said:

The catastrophic ocean-heat wave that is occurring in Florida and spreading quickly to the rest of the western Atlantic and Caribbean presents a huge risk to the health and future of coral reef ecosystems.

The scientists focused on the threatened elkhorn coral for their rescue missions. Elkhorn coral does indeed resemble an elk’s antlers. It’s one of the most important corals in the Caribbean because of the complex habitat it provides marine life and its ability to protect the shoreline from waves and storms. Following a disease in the 1980s, only 3% of elkhorn corals are left. The elkhorn coral were part of an assisted migration experiment, where corals grown on a farm were reintroduced to the national parks. As Kuffner said:

While we know we cannot save every coral; we are focusing on individual corals that represent unique genetic lines that are thought only to exist in certain National Parks.

Whether the corals survive until the cooler temperatures of fall remains to be seen.

The ocean heatwave during the summer of 2023 put many coral reefs under stress. In this image from August 15, 2023, a bleached coral in Florida’s Dry Tortugas gets emergency relief in the form of shade to help reduce light stress. Image via USGS.

Bottom line: Scientists constructed sunshades over bleached corals in two of Florida’s national parks in an effort to protect them from further damage.

Via USGS

The post Florida’s bleached corals get emergency sunshades first appeared on EarthSky.

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Three scuba divers install shade structures over some bleached corals in Biscayne National Park in Florida on August 18, 2023. The summer of 2023 brought a perilous heatwave to the ocean. The corals here are attached to cement blocks as part of a USGS experiment that provides data on corals throughout the western Atlantic. The shade structures could help reduce light stress on the bleached corals. Image via USGS.

Some bleached corals get emergency relief

Coral reefs around the world are in peril from a number of causes. Oil spills, pollution, storms and increasing temperatures can all endanger corals. The summer of 2023 brought some of the highest sea surface temperatures on record. As more and more corals bleached under the ocean heatwave, some scientists sought to provide shelter for the corals in the form of sunshades.

Erecting sunshades in the Dry Tortugas

On August 13, 2023, three scientists from the St. Petersburg Coastal and Marine Science Center went on a mission to protect endangered corals. The scientists donned wetsuits and scuba gear and entered the waters of Dry Tortugas National Park. There, they found the heat already affecting many of the corals.

The heat drained, or bleached, the corals of their color. Coral can survive bleaching, but they are more stressed and likely to die. Bleaching happens when water temperatures reach 87 F (30 C). In Florida this summer, the sea surface temperatures not only hit 87 F, they hit the 90s for extended periods of time, even cracking the 100-degree mark. And it wasn’t just Florida that had high sea surface temperatures, but many places around the globe.

The scientists constructed nearly 40 temporary sunshades over corals in the Dry Tortugas. How would an underwater sunshade help? Ilsa Kuffner, a USGS research marine biologist who participated in the emergency procedure, said:

The shading helps by reducing the sun’s rays. While normally corals need sunlight for their symbionts to photosynthesize, when they are bleached, the sun’s energy instead causes a lot of stress.

The sunshades weren’t the only measure the scientists used in their attempts to save the coral. In addition to the sunshades, the team also spent several evenings adding dim lights to the shaded coral in an effort to attract prey for the coral to feed on.

Other corals also got sunshades

After working in the Dry Tortugas, the scientists went to work in Biscayne National Park. With the help of two more scientists, they erected sunshades there as well. Kuffner said:

The catastrophic ocean-heat wave that is occurring in Florida and spreading quickly to the rest of the western Atlantic and Caribbean presents a huge risk to the health and future of coral reef ecosystems.

The scientists focused on the threatened elkhorn coral for their rescue missions. Elkhorn coral does indeed resemble an elk’s antlers. It’s one of the most important corals in the Caribbean because of the complex habitat it provides marine life and its ability to protect the shoreline from waves and storms. Following a disease in the 1980s, only 3% of elkhorn corals are left. The elkhorn coral were part of an assisted migration experiment, where corals grown on a farm were reintroduced to the national parks. As Kuffner said:

While we know we cannot save every coral; we are focusing on individual corals that represent unique genetic lines that are thought only to exist in certain National Parks.

Whether the corals survive until the cooler temperatures of fall remains to be seen.

The ocean heatwave during the summer of 2023 put many coral reefs under stress. In this image from August 15, 2023, a bleached coral in Florida’s Dry Tortugas gets emergency relief in the form of shade to help reduce light stress. Image via USGS.

Bottom line: Scientists constructed sunshades over bleached corals in two of Florida’s national parks in an effort to protect them from further damage.

Via USGS

The post Florida’s bleached corals get emergency sunshades first appeared on EarthSky.

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Psyche mission to explore priceless asteroid

Artist’s concept of Psyche spacecraft. It’ll launch October 5, 2023, with the goal of exploring the surface of asteroid Psyche. Is Psyche a super-dense metal asteroid? Or more like a “rubble pile?” Either way … in terms of mining … it’s priceless. Image via NASA/ JPL-Caltech/ ASU/ Space Systems Loral/ Peter Rubin.

Psyche is an asteroid floating in our solar system’s asteroid belt between the 4th planet Mars and 5th planet Jupiter. Some scientists believe the asteroid is the remains of an iron-rich core from a failed planet, whose metallic resources are worth some $10,000 quadrillion (that’s 15 more zeroes). But others aren’t so sure.

Arizona State University is leading a mission that’ll send an exploratory spacecraft to asteroid Psyche. The Psyche mission is set to launch from Kennedy Space Center in Florida on October 5, 2023. It’s due to arrive at the asteroid in 2029.

Psyche mission goals

The Psyche spacecraft will orbit the asteroid for three years. In that time, scientists hope to learn more about the origins of the asteroid and whether it was a planetesimal, that is, a solid chunk of stuff leftover from the formation of our solar system some 4.5 billion years ago.

They also want to explore Psyche’s topography (the features of its land surface) and determine the age of its surface. They say it’ll give them insight into the interiors of all the terrestrial planets, including Earth.

But the big question is … is Psyche a true metal asteroid, as once believed? Or is it closer to what scientists call a “rubble pile?”

There’s no way (at present) to put a true price on space objects such as asteroids. But many have tried to estimate the worth of asteroid Psyche, with its metal-rich composition. One estimate suggests a massive, metal-rich object would be worth $10,000 quadrillion, more than the entire economy of Earth.

If Psyche isn’t as dense as once believed, this estimate will go down.

Still, either way, Psyche will be worth a lot! And, to scientists, it’ll remain … priceless.

Mining the asteroid?

Now, about that $10,000 quadrillion worth of metals in Psyche … NASA is not on a mission to mine an asteroid. Instead, NASA says, Psyche is a science mission to learn more about asteroids and the formation of terrestrial planets.

No one on Earth is yet at a stage where we can successfully go to an asteroid and mine it. But private companies are working on how to mine asteroids. Learn more about the asteroid mining process in the video below.

More about Psyche

Italian astronomer Annibale de Gasparis discovered Psyche in 1852. It was the 16th asteroid discovered. De Gasparis named the asteroid after the Greek goddess of the soul.

Psyche measures approximately 140 miles (225 km) in diameter, with a surface area of about 64,000 square miles (165,800 km²). Current estimates of its density are 3,400 to 4,100 kg/m³. This density measurement would mean the asteroid is 30 to 60% metal by volume.

Scientists speculate that Psyche was once a young planetesimal with a composition that separated out into an iron core and a rocky mantel, but a collision ripped away the rocky exterior. Thus, we may get a first-row seat in viewing the inside of a terrestrial planet.

Artist’s concept of asteroid Psyche. Image via Maxar/ ASU/ P. Rubin/ NASA/ JPL-Caltech.

The mission’s instruments

The Psyche mission will carry three primary instruments: a multispectral imager, a gamma ray and neutron spectrometer and a magnetometer. These instruments will be investigating the first metal space object that humankind has ever visited.

The imagers will take pictures while the spectrometer will measure the elemental composition of Psyche. The magnetometer will check for any remaining magnetic field, which will be an indication of whether or not Psyche was once a planetary core.

Psyche will also have an X-band radio telecommunications system that will help map the asteroid’s gravity and structure. The system is also used in sending commands to the spacecraft and receiving data back on Earth.

After the October 5, 2023, launch, the Psyche spacecraft will have a flyby of Mars in May 2026 for a gravity assist. The spacecraft will orbit the asteroid for 3 years while it collects data. Image via NASA/ ASU.

Bottom line: The Psyche mission will launch on October 5, 2023, on a mission to explore the metal-rich asteroid Psyche.

Via NASA

Via ASU

The post Psyche mission to explore priceless asteroid first appeared on EarthSky.

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Artist’s concept of Psyche spacecraft. It’ll launch October 5, 2023, with the goal of exploring the surface of asteroid Psyche. Is Psyche a super-dense metal asteroid? Or more like a “rubble pile?” Either way … in terms of mining … it’s priceless. Image via NASA/ JPL-Caltech/ ASU/ Space Systems Loral/ Peter Rubin.

Psyche is an asteroid floating in our solar system’s asteroid belt between the 4th planet Mars and 5th planet Jupiter. Some scientists believe the asteroid is the remains of an iron-rich core from a failed planet, whose metallic resources are worth some $10,000 quadrillion (that’s 15 more zeroes). But others aren’t so sure.

Arizona State University is leading a mission that’ll send an exploratory spacecraft to asteroid Psyche. The Psyche mission is set to launch from Kennedy Space Center in Florida on October 5, 2023. It’s due to arrive at the asteroid in 2029.

Psyche mission goals

The Psyche spacecraft will orbit the asteroid for three years. In that time, scientists hope to learn more about the origins of the asteroid and whether it was a planetesimal, that is, a solid chunk of stuff leftover from the formation of our solar system some 4.5 billion years ago.

They also want to explore Psyche’s topography (the features of its land surface) and determine the age of its surface. They say it’ll give them insight into the interiors of all the terrestrial planets, including Earth.

But the big question is … is Psyche a true metal asteroid, as once believed? Or is it closer to what scientists call a “rubble pile?”

There’s no way (at present) to put a true price on space objects such as asteroids. But many have tried to estimate the worth of asteroid Psyche, with its metal-rich composition. One estimate suggests a massive, metal-rich object would be worth $10,000 quadrillion, more than the entire economy of Earth.

If Psyche isn’t as dense as once believed, this estimate will go down.

Still, either way, Psyche will be worth a lot! And, to scientists, it’ll remain … priceless.

Mining the asteroid?

Now, about that $10,000 quadrillion worth of metals in Psyche … NASA is not on a mission to mine an asteroid. Instead, NASA says, Psyche is a science mission to learn more about asteroids and the formation of terrestrial planets.

No one on Earth is yet at a stage where we can successfully go to an asteroid and mine it. But private companies are working on how to mine asteroids. Learn more about the asteroid mining process in the video below.

More about Psyche

Italian astronomer Annibale de Gasparis discovered Psyche in 1852. It was the 16th asteroid discovered. De Gasparis named the asteroid after the Greek goddess of the soul.

Psyche measures approximately 140 miles (225 km) in diameter, with a surface area of about 64,000 square miles (165,800 km²). Current estimates of its density are 3,400 to 4,100 kg/m³. This density measurement would mean the asteroid is 30 to 60% metal by volume.

Scientists speculate that Psyche was once a young planetesimal with a composition that separated out into an iron core and a rocky mantel, but a collision ripped away the rocky exterior. Thus, we may get a first-row seat in viewing the inside of a terrestrial planet.

Artist’s concept of asteroid Psyche. Image via Maxar/ ASU/ P. Rubin/ NASA/ JPL-Caltech.

The mission’s instruments

The Psyche mission will carry three primary instruments: a multispectral imager, a gamma ray and neutron spectrometer and a magnetometer. These instruments will be investigating the first metal space object that humankind has ever visited.

The imagers will take pictures while the spectrometer will measure the elemental composition of Psyche. The magnetometer will check for any remaining magnetic field, which will be an indication of whether or not Psyche was once a planetary core.

Psyche will also have an X-band radio telecommunications system that will help map the asteroid’s gravity and structure. The system is also used in sending commands to the spacecraft and receiving data back on Earth.

After the October 5, 2023, launch, the Psyche spacecraft will have a flyby of Mars in May 2026 for a gravity assist. The spacecraft will orbit the asteroid for 3 years while it collects data. Image via NASA/ ASU.

Bottom line: The Psyche mission will launch on October 5, 2023, on a mission to explore the metal-rich asteroid Psyche.

Via NASA

Via ASU

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Ants, little but tough: Lifeform of the week

Closeup of a red ant covered in pollen. Learn more about ants here. Image via Egor Kamelev/ Pexels.

Ants are common insects, but they have some unique capabilities. For example, they have legendary communication skills that allow their colonies to function as superorganisms.

We are newbies in the animal kingdom, but ants have been living since the Cretaceous, arising some 140 to 168 million years ago. Individually, ants are the longest-lived insects. Unlike some bugs that might only live for days or even hours, the queen ant of one particular species – the Pogonomyrmex Owyheei – can live up to 30 years.

There are 20 quadrillion ants on Earth. That’s 2.5 million ants for every human. Ants are members of the family Formicidae. There are more than 12,000 species, and some experts estimate 20,000 exist.

They can be found almost anywhere in the world, with the exception of Antarctica, Iceland, Greenland and some island nations.

A black ant on a stem. Image via Alexandre Ribeiro/ Unsplash.

Ants’ appearance

Ants range in size from minuscule up to 1 inch (3 cm) long. They are usually black, brown, red or yellow.

Ants don’t have ears, and some of them don’t have eyes! Ants “listen” by feeling vibrations from the ground through their feet, and eyeless ants such as the driver ant species can communicate by using their antennae.

Ants have elbowed antennae and narrow “waists” between the abdomen and thorax. Some ants have wings. Their front wings are longer than their hind wings. The presence of wings indicates an ant’s fertility. Ants with wings are either females that are fertile or males whose job it is to mate with them.

Only fertile females and males have wings. Image via Egor Kamelev/ Pexels.

Members of the colony

In a colony, you can find females (workers or queens) and males. While females are diploid (hatched from fertilized eggs, hence possessing two sets of chromosomes, one from the mother and one from her male mate), males are haploid (hatched from unfertilized eggs, hence have just one set of chromosomes, from the mother). Thus, males do not have a father.

Queens are reproductive females that are fully winged in most species.
Workers are non-reproductive (sterile) females that are always wingless. They form the bulk of individuals within a colony.
Males are fully winged (mostly). They are generally present within a colony for only a short time each year and typically live a few weeks, dying very soon after mating.

A queen ant with worker ants. Image via Andreas/ Pixabay.

Typical cycle for a worker ant

Egg: Laid in the ant colony and looked after by other workers.
Larva: Once it emerges from the egg, the larva then begins to develop.
Adult: It can take around 6-10 weeks for an ant to reach the adult stage.

For the queen in any colony, their lifespan may last up to around 15 years, while the worker ants live for roughly seven years. This is, of course, if they can avoid predators and other dangers. For a reproductive male – one of the flying ant types – the lifespan is much shorter at around two weeks. This is because when they’re done mating, they die.

Most of the ants a person sees are female. Male ants, also called “drones,’ do not perform any work in the colony. Their only job is to fertilize the queen ant so she can lay eggs and support the population in the nest.

What are their characteristics?

The ant is one of the world’s strongest creatures in relation to its size. A single ant can carry 50 times its own body weight, and they’ll even work together to move bigger objects as a group!

Ants are very strong in relation to their size. Here’s a red ant carrying a piece of white mushroom. Image via James Wainscoat/ Unsplash.

Ants hold the record for the fastest movement in the animal kingdom. A species of trap jaw ant can close its jaws at 140 mph (125 kph), which it uses to kill its prey or injure predators.

The largest ant nest ever found was more than 3,700 miles (6,000 km) wide. Found in Argentina in 2000, the enormous colony housed 33 ant populations that had merged into one giant supercolony, with millions of nests and billions of workers.

Ants’ behavior and diet

As social insects, ants live in structured nest communities that may be located underground, in ground-level mounds or in trees.

Ants work together. They move big objects as a group, create living bridges and even float in rafts made up of their own bodies. Image via Igor Chuxlancev/ Wikipedia (CC BY 4.0).

A single ant colony can contain hundreds of thousands of individual ants. Communities are headed by a queen or queens; some species can have as few as two or up to thousands of queens. Queens lay thousands of eggs to ensure the survival of the colony.

Worker ants, the most visible colony members, are females that never reproduce, but instead forage for food, care for the queen’s offspring, work on the nest, and protect the community.

Ants communicate and cooperate by secreting pheromones, or scent chemicals, released through their body to send messages to other ants. They send out warnings when danger’s near, leave trails of pheremones leading to food sources and even use them to attract a mate, like a love potion. How romantic!

They typically eat nectar, seeds, fungus or insects. However, some species have diets that are more unusual. Army ants, with their large mandibles and painful stings, may prey on reptiles, birds or even small mammals.

Ant colonies are so efficient that they can pass useful knowledge between generations. This kind of communal knowledge is essential for defense, so ants can easily differentiate friendly and hostile forces.

An amazing social system

Ants dispose of their dead. They even have undertakers to do this. When an ant dies inside the nest, they carry the body outside to prevent diseases and infections from spreading and affecting the rest of the colony. When an ant dies, its scent changes because the corpse releases something called oleic acid. Other ants detect this new chemical and carry the corpse.

Ants teach their young. As social insects, they have a very advanced system. This way, each group has a specialty, like foraging, cleaning or caretaking of eggs and baby ants.

What’s really interesting is that they’re not born with special skills. They do what we humans do; they learn from those around them. There are teachers that show them how to do a task, and if they are too slow or lack that talent, then they must do another job that doesn’t require special abilities.

Each group of ants has a specialty, but ants are not born with special skills; they develop them by practicing. Also, they have good teachers. Image via Prince Patel/ Unsplash.

How an ant colony begins

Ants can harvest, herd and milk. They actually started farming before we did, 50 million years ago. Before moving out of her birth nest, a young queen must sneak inside the garden she used to live in to take away some seeds and fungal pellets to start her own garden and feed her brood.

So, she takes a blob of fungus in her mouth, taken from the established fungal garden she used to live in, and leaps in the air for a mating flight, gathering enough sperm to keep laying eggs for the rest of her life, which can be as long as 10 years. Then she lands, sheds her wings, finds a burrow in the ground, and starts a new colony.

She spits out her fungal blob, and it begins to grow. The queen lays her eggs in the fungus. The larvae feed on it, and once the first worker ants hatch, they help the queen to tend the garden.

Eco-friendly ants

Ants use herbicides and disinfectant in their fungal gardens. But their substances are far more eco-friendly than human-made ones. The fungal gardens they grow are also home to a virulent type of fungus that kills the fungal crops, preventing them from spreading.

Ants have bacteria at their disposal; they carry them on their cuticles (the hard outer layer they have instead of skin). These bacteria produce an antibiotic that suppresses the growth of the fungal weed. In their nests, they use several substances that inhibit the spread of parasites or weeds.

Leafcutter ants are industrious creatures known for expertly carving up foliage and then carrying it back in pieces to their colony. They use the leaves to farm fungus.

Several species of ants have a special symbiotic relationship with aphids. Aphids feed primarily on the sap from plants and secrete a liquid called honeydew. This secretion is very sugar-rich, and ants crave it. It’s a great food source.

As a result, a system has been hashed out by these insects wherein the ants herd the aphids around to the juiciest parts of plants, protect them from predators, and carry them into their nests at night and for winter. In return, they are allowed to “milk” the aphids, tapping the aphids with their antennae, coaxing them to secrete their honeydew, which is then lapped up by the ant. The little bugs are considered pests by every farmer on earth, except for their friendly six-legged keepers, the herder ants, which treat the bugs as their dairy cows.

Ants protect aphids. These little bugs are a pest for many farmers, but for ants, they are a source for one of their favorite dishes, honeydew. Image via Petr Ganaj/ Pexels.

Underground cities

Ants build amazingly complex and stable structures. From the outside, you might only see a hole disappearing into the ground, but beneath the surface, there are many tunnels, branches and chambers that serve as home for the colony’s queen, as nurseries for the young, as farms for fungus cultivated for food, and as trash dumps. They are underground cities, some of them home to millions of individuals, reaching as far as 25 feet (8 meters) underground, often lasting for decades.

Ant nests are architectural pieces of art. This is a Pogonomyrmex badius nest. Image via Charles F. Badland/ Wikipedia.

This kind of construction would be an impressive undertaking for most creatures, but when performed by animals that don’t get much bigger than your fingernail, it is especially remarkable.

Watch this amazing video of an excavation of an underground ant city.

Unusual ants

Within the many thousands of known ant species, there are many that are unique, resulting in the development of special physical characteristics and interesting behavior.

For example, ants have a variety of biological defenses. Fire ants might be little, but they bite and sting with a venom called solenopsin, which causes a burning sensation, hence the name “fire ant.” They can also survive floods by clumping together to float on the water’s surface.

Other species, like the Pheidole drogon, have evolved to grow spikes or spines from their exoskeletons.

One Amazon species, the Allomerus decemarticulatus, cooperatively builds extensive traps from plant fiber. When an insect steps on one of the trap’s many holes, hundreds of ants inside use the openings to seize it with their jaws.

The bullet ant is said to have the most painful sting in the world. Living in humid jungle areas such as the Amazon, their sting has been compared to being hit by a bullet.

Culture and history

Ants can be used to stitch up wounds. Minor wounds are normally just annoying, with advanced medicine a call away. But imagine you’re in the middle of nowhere and with no first-aid kit or hospital. Then you could use the army ants’ strong pincers. In Maasai tribes, they have the ant bite on both sides of the wound, break off its body and leave behind the head. It can mean the difference between life and death when no other resources are available.

Some ants have big, strong pincers that they use to prey on bigger animals. These ants can be used to heal little wounds. Image via Egor Kamelev/ Pexels.

Thank you to the amazing photographers from Pexels, Unsplash and Wikipedia.

Bottom line: Ants are common insects with unique capabilities. They can be found almost anywhere in the world and can harvest, herd and milk. They can also build amazingly complex and stable underground cities.

Read more lifeform of the week articles

The post Ants, little but tough: Lifeform of the week first appeared on EarthSky.

from EarthSky https://ift.tt/s0lRPQh

Closeup of a red ant covered in pollen. Learn more about ants here. Image via Egor Kamelev/ Pexels.

Ants are common insects, but they have some unique capabilities. For example, they have legendary communication skills that allow their colonies to function as superorganisms.

We are newbies in the animal kingdom, but ants have been living since the Cretaceous, arising some 140 to 168 million years ago. Individually, ants are the longest-lived insects. Unlike some bugs that might only live for days or even hours, the queen ant of one particular species – the Pogonomyrmex Owyheei – can live up to 30 years.

There are 20 quadrillion ants on Earth. That’s 2.5 million ants for every human. Ants are members of the family Formicidae. There are more than 12,000 species, and some experts estimate 20,000 exist.

They can be found almost anywhere in the world, with the exception of Antarctica, Iceland, Greenland and some island nations.

A black ant on a stem. Image via Alexandre Ribeiro/ Unsplash.

Ants’ appearance

Ants range in size from minuscule up to 1 inch (3 cm) long. They are usually black, brown, red or yellow.

Ants don’t have ears, and some of them don’t have eyes! Ants “listen” by feeling vibrations from the ground through their feet, and eyeless ants such as the driver ant species can communicate by using their antennae.

Ants have elbowed antennae and narrow “waists” between the abdomen and thorax. Some ants have wings. Their front wings are longer than their hind wings. The presence of wings indicates an ant’s fertility. Ants with wings are either females that are fertile or males whose job it is to mate with them.

Only fertile females and males have wings. Image via Egor Kamelev/ Pexels.

Members of the colony

In a colony, you can find females (workers or queens) and males. While females are diploid (hatched from fertilized eggs, hence possessing two sets of chromosomes, one from the mother and one from her male mate), males are haploid (hatched from unfertilized eggs, hence have just one set of chromosomes, from the mother). Thus, males do not have a father.

Queens are reproductive females that are fully winged in most species.
Workers are non-reproductive (sterile) females that are always wingless. They form the bulk of individuals within a colony.
Males are fully winged (mostly). They are generally present within a colony for only a short time each year and typically live a few weeks, dying very soon after mating.

A queen ant with worker ants. Image via Andreas/ Pixabay.

Typical cycle for a worker ant

Egg: Laid in the ant colony and looked after by other workers.
Larva: Once it emerges from the egg, the larva then begins to develop.
Adult: It can take around 6-10 weeks for an ant to reach the adult stage.

For the queen in any colony, their lifespan may last up to around 15 years, while the worker ants live for roughly seven years. This is, of course, if they can avoid predators and other dangers. For a reproductive male – one of the flying ant types – the lifespan is much shorter at around two weeks. This is because when they’re done mating, they die.

Most of the ants a person sees are female. Male ants, also called “drones,’ do not perform any work in the colony. Their only job is to fertilize the queen ant so she can lay eggs and support the population in the nest.

What are their characteristics?

The ant is one of the world’s strongest creatures in relation to its size. A single ant can carry 50 times its own body weight, and they’ll even work together to move bigger objects as a group!

Ants are very strong in relation to their size. Here’s a red ant carrying a piece of white mushroom. Image via James Wainscoat/ Unsplash.

Ants hold the record for the fastest movement in the animal kingdom. A species of trap jaw ant can close its jaws at 140 mph (125 kph), which it uses to kill its prey or injure predators.

The largest ant nest ever found was more than 3,700 miles (6,000 km) wide. Found in Argentina in 2000, the enormous colony housed 33 ant populations that had merged into one giant supercolony, with millions of nests and billions of workers.

Ants’ behavior and diet

As social insects, ants live in structured nest communities that may be located underground, in ground-level mounds or in trees.

Ants work together. They move big objects as a group, create living bridges and even float in rafts made up of their own bodies. Image via Igor Chuxlancev/ Wikipedia (CC BY 4.0).

A single ant colony can contain hundreds of thousands of individual ants. Communities are headed by a queen or queens; some species can have as few as two or up to thousands of queens. Queens lay thousands of eggs to ensure the survival of the colony.

Worker ants, the most visible colony members, are females that never reproduce, but instead forage for food, care for the queen’s offspring, work on the nest, and protect the community.

Ants communicate and cooperate by secreting pheromones, or scent chemicals, released through their body to send messages to other ants. They send out warnings when danger’s near, leave trails of pheremones leading to food sources and even use them to attract a mate, like a love potion. How romantic!

They typically eat nectar, seeds, fungus or insects. However, some species have diets that are more unusual. Army ants, with their large mandibles and painful stings, may prey on reptiles, birds or even small mammals.

Ant colonies are so efficient that they can pass useful knowledge between generations. This kind of communal knowledge is essential for defense, so ants can easily differentiate friendly and hostile forces.

An amazing social system

Ants dispose of their dead. They even have undertakers to do this. When an ant dies inside the nest, they carry the body outside to prevent diseases and infections from spreading and affecting the rest of the colony. When an ant dies, its scent changes because the corpse releases something called oleic acid. Other ants detect this new chemical and carry the corpse.

Ants teach their young. As social insects, they have a very advanced system. This way, each group has a specialty, like foraging, cleaning or caretaking of eggs and baby ants.

What’s really interesting is that they’re not born with special skills. They do what we humans do; they learn from those around them. There are teachers that show them how to do a task, and if they are too slow or lack that talent, then they must do another job that doesn’t require special abilities.

Each group of ants has a specialty, but ants are not born with special skills; they develop them by practicing. Also, they have good teachers. Image via Prince Patel/ Unsplash.

How an ant colony begins

Ants can harvest, herd and milk. They actually started farming before we did, 50 million years ago. Before moving out of her birth nest, a young queen must sneak inside the garden she used to live in to take away some seeds and fungal pellets to start her own garden and feed her brood.

So, she takes a blob of fungus in her mouth, taken from the established fungal garden she used to live in, and leaps in the air for a mating flight, gathering enough sperm to keep laying eggs for the rest of her life, which can be as long as 10 years. Then she lands, sheds her wings, finds a burrow in the ground, and starts a new colony.

She spits out her fungal blob, and it begins to grow. The queen lays her eggs in the fungus. The larvae feed on it, and once the first worker ants hatch, they help the queen to tend the garden.

Eco-friendly ants

Ants use herbicides and disinfectant in their fungal gardens. But their substances are far more eco-friendly than human-made ones. The fungal gardens they grow are also home to a virulent type of fungus that kills the fungal crops, preventing them from spreading.

Ants have bacteria at their disposal; they carry them on their cuticles (the hard outer layer they have instead of skin). These bacteria produce an antibiotic that suppresses the growth of the fungal weed. In their nests, they use several substances that inhibit the spread of parasites or weeds.

Leafcutter ants are industrious creatures known for expertly carving up foliage and then carrying it back in pieces to their colony. They use the leaves to farm fungus.

Several species of ants have a special symbiotic relationship with aphids. Aphids feed primarily on the sap from plants and secrete a liquid called honeydew. This secretion is very sugar-rich, and ants crave it. It’s a great food source.

As a result, a system has been hashed out by these insects wherein the ants herd the aphids around to the juiciest parts of plants, protect them from predators, and carry them into their nests at night and for winter. In return, they are allowed to “milk” the aphids, tapping the aphids with their antennae, coaxing them to secrete their honeydew, which is then lapped up by the ant. The little bugs are considered pests by every farmer on earth, except for their friendly six-legged keepers, the herder ants, which treat the bugs as their dairy cows.

Ants protect aphids. These little bugs are a pest for many farmers, but for ants, they are a source for one of their favorite dishes, honeydew. Image via Petr Ganaj/ Pexels.

Underground cities

Ants build amazingly complex and stable structures. From the outside, you might only see a hole disappearing into the ground, but beneath the surface, there are many tunnels, branches and chambers that serve as home for the colony’s queen, as nurseries for the young, as farms for fungus cultivated for food, and as trash dumps. They are underground cities, some of them home to millions of individuals, reaching as far as 25 feet (8 meters) underground, often lasting for decades.

Ant nests are architectural pieces of art. This is a Pogonomyrmex badius nest. Image via Charles F. Badland/ Wikipedia.

This kind of construction would be an impressive undertaking for most creatures, but when performed by animals that don’t get much bigger than your fingernail, it is especially remarkable.

Watch this amazing video of an excavation of an underground ant city.

Unusual ants

Within the many thousands of known ant species, there are many that are unique, resulting in the development of special physical characteristics and interesting behavior.

For example, ants have a variety of biological defenses. Fire ants might be little, but they bite and sting with a venom called solenopsin, which causes a burning sensation, hence the name “fire ant.” They can also survive floods by clumping together to float on the water’s surface.

Other species, like the Pheidole drogon, have evolved to grow spikes or spines from their exoskeletons.

One Amazon species, the Allomerus decemarticulatus, cooperatively builds extensive traps from plant fiber. When an insect steps on one of the trap’s many holes, hundreds of ants inside use the openings to seize it with their jaws.

The bullet ant is said to have the most painful sting in the world. Living in humid jungle areas such as the Amazon, their sting has been compared to being hit by a bullet.

Culture and history

Ants can be used to stitch up wounds. Minor wounds are normally just annoying, with advanced medicine a call away. But imagine you’re in the middle of nowhere and with no first-aid kit or hospital. Then you could use the army ants’ strong pincers. In Maasai tribes, they have the ant bite on both sides of the wound, break off its body and leave behind the head. It can mean the difference between life and death when no other resources are available.

Some ants have big, strong pincers that they use to prey on bigger animals. These ants can be used to heal little wounds. Image via Egor Kamelev/ Pexels.

Thank you to the amazing photographers from Pexels, Unsplash and Wikipedia.

Bottom line: Ants are common insects with unique capabilities. They can be found almost anywhere in the world and can harvest, herd and milk. They can also build amazingly complex and stable underground cities.

Read more lifeform of the week articles

The post Ants, little but tough: Lifeform of the week first appeared on EarthSky.

from EarthSky https://ift.tt/s0lRPQh

Equinox sun rises due east and sets due west

The equinox is coming up on September 23. At the equinoxes, the ecliptic and the celestial equator intersect. See the intersection point on this imaginary great circle, representing the dome of Earth’s sky? The celestial equator is is directly above Earth’s equator. The ecliptic is the sun’s apparent path across our sky. And the celestial equator intersects your horizon at points due east and due west. That’s why – at every equinox, no matter where you are on the globe – the sun, on the celestial equator, rises due east and sets due west. Read more about the equinox sun below. Image via NASA.

The September equinox happens at 6:50 UTC (1:50 a.m. CDT) on September 23, 2023.

The equinox sun rises due east and sets due west

It’s not true that day and night are precisely equal on the day of an equinox. But here’s an equinox fact that is true. The sun rises due east and sets due west at the equinox. It might seem counterintuitive. But it’s true no matter where you live on Earth (except at the North and South Poles). Here’s how to visualize it.

To understand the nearly due-east and due-west rising and setting of an equinox sun, you have to think of the reality of Earth in space. First think about why the sun’s path across our sky shifts from season to season. That’s because our world is tilted on its axis with respect to its orbit around the sun.

The fact is, our seasons result from the Earth’s rotational axis tilting 23.5 degrees out of the perpendicular to the ecliptic, or Earth’s orbital plane. Image via weather.gov.

Now think about what is an equinox. It’s an event that happens on the imaginary dome of Earth’s sky. And it marks that special moment when the sun crosses the celestial equator going from one hemisphere to the other. Of course, it also represents a point in Earth’s orbit.

The celestial equator

The celestial equator is a great circle dividing the imaginary celestial sphere into its northern and southern hemispheres. Additionally, the celestial equator wraps the sky directly above Earth’s equator. Following the September equinox, the sun crosses the celestial equator to enter the sky’s Southern Hemisphere.

All these components are imaginary, yet what happens at every equinox is very real. In fact, it’s as real as the sun’s passage across the sky each day and as real as the change of seasons.

It’s the same all over the globe

So no matter where you are on Earth (except for the North and South Poles), you have a due east and due west point on your horizon. That point marks the intersection of your horizon with the celestial equator, the imaginary great circle above the true equator of Earth.

And that’s why the sun rises close to due east and sets close to due west, for all of us, at the equinox. The fact is, the equinox sun is on the celestial equator. Which means, no matter where you are on Earth, the celestial equator intersects your horizon at due east and due west.

This fact makes the day of an equinox a good day for finding east and west from your yard or favorite site for watching the sky. Just go outside around sunset or sunrise and notice the location of the sun on the horizon with respect to familiar landmarks.

If you do this, you’ll be able to use those landmarks to find those cardinal directions in the weeks and months ahead. Plus, you’ll know those directions long after Earth has moved on in its orbit around the sun.

The history of the seasons

Our ancestors may not have understood the equinoxes and solstices as events that occur during Earth’s yearly orbit around the sun. But if they were observant – and some were very observant indeed – they surely marked the day of the equinox as being midway between the sun’s lowest path across the sky in winter and highest path across the sky in summer.

Now we can say with reasonably high accuracy that the sun rises due east and sets due west on the day of the equinox. And this is the same for everyone around the globe.

If you are seeking more precision for the sunrise/sunset direction in your part of the world, check out the altitude/azimuth for the sun via timeanddate.com.

Raúl Cortés caught the March equinox sun at sunrise in 2021. Thanks, Raúl!

Bottom line: The 2023 September equinox occurs on September 23 at 6:50 UTC (1:50 a.m. CDT). At the equinox, the sun rises and sets due east and due west.

September equinox 2023: Everything you need to know

Hamal: Ancient equinox star

Read more: Celestial coordinates: Declination and Right Ascension

The post Equinox sun rises due east and sets due west first appeared on EarthSky.

from EarthSky https://ift.tt/JUGtsvR

The equinox is coming up on September 23. At the equinoxes, the ecliptic and the celestial equator intersect. See the intersection point on this imaginary great circle, representing the dome of Earth’s sky? The celestial equator is is directly above Earth’s equator. The ecliptic is the sun’s apparent path across our sky. And the celestial equator intersects your horizon at points due east and due west. That’s why – at every equinox, no matter where you are on the globe – the sun, on the celestial equator, rises due east and sets due west. Read more about the equinox sun below. Image via NASA.

The September equinox happens at 6:50 UTC (1:50 a.m. CDT) on September 23, 2023.

The equinox sun rises due east and sets due west

It’s not true that day and night are precisely equal on the day of an equinox. But here’s an equinox fact that is true. The sun rises due east and sets due west at the equinox. It might seem counterintuitive. But it’s true no matter where you live on Earth (except at the North and South Poles). Here’s how to visualize it.

To understand the nearly due-east and due-west rising and setting of an equinox sun, you have to think of the reality of Earth in space. First think about why the sun’s path across our sky shifts from season to season. That’s because our world is tilted on its axis with respect to its orbit around the sun.

The fact is, our seasons result from the Earth’s rotational axis tilting 23.5 degrees out of the perpendicular to the ecliptic, or Earth’s orbital plane. Image via weather.gov.

Now think about what is an equinox. It’s an event that happens on the imaginary dome of Earth’s sky. And it marks that special moment when the sun crosses the celestial equator going from one hemisphere to the other. Of course, it also represents a point in Earth’s orbit.

The celestial equator

The celestial equator is a great circle dividing the imaginary celestial sphere into its northern and southern hemispheres. Additionally, the celestial equator wraps the sky directly above Earth’s equator. Following the September equinox, the sun crosses the celestial equator to enter the sky’s Southern Hemisphere.

All these components are imaginary, yet what happens at every equinox is very real. In fact, it’s as real as the sun’s passage across the sky each day and as real as the change of seasons.

It’s the same all over the globe

So no matter where you are on Earth (except for the North and South Poles), you have a due east and due west point on your horizon. That point marks the intersection of your horizon with the celestial equator, the imaginary great circle above the true equator of Earth.

And that’s why the sun rises close to due east and sets close to due west, for all of us, at the equinox. The fact is, the equinox sun is on the celestial equator. Which means, no matter where you are on Earth, the celestial equator intersects your horizon at due east and due west.

This fact makes the day of an equinox a good day for finding east and west from your yard or favorite site for watching the sky. Just go outside around sunset or sunrise and notice the location of the sun on the horizon with respect to familiar landmarks.

If you do this, you’ll be able to use those landmarks to find those cardinal directions in the weeks and months ahead. Plus, you’ll know those directions long after Earth has moved on in its orbit around the sun.

The history of the seasons

Our ancestors may not have understood the equinoxes and solstices as events that occur during Earth’s yearly orbit around the sun. But if they were observant – and some were very observant indeed – they surely marked the day of the equinox as being midway between the sun’s lowest path across the sky in winter and highest path across the sky in summer.

Now we can say with reasonably high accuracy that the sun rises due east and sets due west on the day of the equinox. And this is the same for everyone around the globe.

If you are seeking more precision for the sunrise/sunset direction in your part of the world, check out the altitude/azimuth for the sun via timeanddate.com.

Raúl Cortés caught the March equinox sun at sunrise in 2021. Thanks, Raúl!

Bottom line: The 2023 September equinox occurs on September 23 at 6:50 UTC (1:50 a.m. CDT). At the equinox, the sun rises and sets due east and due west.

September equinox 2023: Everything you need to know

Hamal: Ancient equinox star

Read more: Celestial coordinates: Declination and Right Ascension

The post Equinox sun rises due east and sets due west first appeared on EarthSky.

from EarthSky https://ift.tt/JUGtsvR

Year’s fastest sunsets happen around equinoxes

View at EarthSky Community Photos. | Jim Grant caught this sunset with a green flash at the Ocean Beach Pier in San Diego, California, on July 19, 2023. Jim wrote: “I knew the sunset was going to be stunning and I started tracking the boat hoping to get it centered in the sun. The green rim and green flash above were a bonus.” Thank you, Jim! Read more about the fastest sunsets below.

Year’s fastest sunsets and sunrises

The September equinox will arrive Saturday (September 23, 2023) at 6:50 UTC. And here’s a little-known equinox phenomenon: the sun sets faster around the time of an equinox. The fastest sunsets (and sunrises) occur at or near the equinoxes. On the other hand, the slowest sunsets (and sunrises) occur at or near the solstices. It’s true whether you live in the Northern or Southern Hemisphere.

And, by the way, when we say sunset here, we’re talking about the actual number of minutes it takes for the body of the sun to sink below the western horizon.

Why does the sun set so quickly around the equinoxes? It’s because, at every equinox, the sun rises due east and sets due west. So, that means – on the day of an equinox – the setting sun hits the horizon at its steepest possible angle.

View at EarthSky Community Photos. | Ragini Chaturvedi, a frequent contributor to our pages, caught this sunrise from Palouse, Washington, on June 22, 2021, the day after the solstice. She wrote: “Encouraged by the EarthSky community, I share another phenomenal view of Palouse, Washington. At the elevation of 3,612 feet [1,100 m], the Steptoe Butte State Park presents such a super early sunrise view. Breathtaking.” Thank you, Ragini!

Year’s slowest sunsets and sunrises

Meanwhile, at a solstice, the sun is setting farthest north or farthest south of due west. And, the farther the sun sets from due west along the horizon, the shallower the angle of the setting sun. So that means a longer duration for sunset at the solstices.

Also, the sunset duration varies by latitude. Farther north or south on the Earth’s globe, the duration of sunset lasts longer. Closer to the equator, the duration is shorter. But let’s just consider one latitude, 40 degrees north, the latitude of Denver or Philadelphia in the United States; parts of Spain; and Beijing, China.

At that latitude, on the day of equinox, the sun sets in about 2 3/4 minutes.

On the other hand, the solstice sun sets in roughly 3 1/4 minutes at 40 degrees latitude.

The fact is, the equinox is an event that takes place in Earth’s orbit around the sun. Image via National Weather Service/ weather.gov.

Bottom line: The fastest sunsets of the year are happening now, around the time of the September equinox.

All you need to know about the September equinox

Are day and night equal on the equinox?

Help support EarthSky! Visit the EarthSky store for to see the great selection of educational tools and team gear we have to offer.

The post Year’s fastest sunsets happen around equinoxes first appeared on EarthSky.

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View at EarthSky Community Photos. | Jim Grant caught this sunset with a green flash at the Ocean Beach Pier in San Diego, California, on July 19, 2023. Jim wrote: “I knew the sunset was going to be stunning and I started tracking the boat hoping to get it centered in the sun. The green rim and green flash above were a bonus.” Thank you, Jim! Read more about the fastest sunsets below.

Year’s fastest sunsets and sunrises

The September equinox will arrive Saturday (September 23, 2023) at 6:50 UTC. And here’s a little-known equinox phenomenon: the sun sets faster around the time of an equinox. The fastest sunsets (and sunrises) occur at or near the equinoxes. On the other hand, the slowest sunsets (and sunrises) occur at or near the solstices. It’s true whether you live in the Northern or Southern Hemisphere.

And, by the way, when we say sunset here, we’re talking about the actual number of minutes it takes for the body of the sun to sink below the western horizon.

Why does the sun set so quickly around the equinoxes? It’s because, at every equinox, the sun rises due east and sets due west. So, that means – on the day of an equinox – the setting sun hits the horizon at its steepest possible angle.

View at EarthSky Community Photos. | Ragini Chaturvedi, a frequent contributor to our pages, caught this sunrise from Palouse, Washington, on June 22, 2021, the day after the solstice. She wrote: “Encouraged by the EarthSky community, I share another phenomenal view of Palouse, Washington. At the elevation of 3,612 feet [1,100 m], the Steptoe Butte State Park presents such a super early sunrise view. Breathtaking.” Thank you, Ragini!

Year’s slowest sunsets and sunrises

Meanwhile, at a solstice, the sun is setting farthest north or farthest south of due west. And, the farther the sun sets from due west along the horizon, the shallower the angle of the setting sun. So that means a longer duration for sunset at the solstices.

Also, the sunset duration varies by latitude. Farther north or south on the Earth’s globe, the duration of sunset lasts longer. Closer to the equator, the duration is shorter. But let’s just consider one latitude, 40 degrees north, the latitude of Denver or Philadelphia in the United States; parts of Spain; and Beijing, China.

At that latitude, on the day of equinox, the sun sets in about 2 3/4 minutes.

On the other hand, the solstice sun sets in roughly 3 1/4 minutes at 40 degrees latitude.

The fact is, the equinox is an event that takes place in Earth’s orbit around the sun. Image via National Weather Service/ weather.gov.

Bottom line: The fastest sunsets of the year are happening now, around the time of the September equinox.

All you need to know about the September equinox

Are day and night equal on the equinox?

Help support EarthSky! Visit the EarthSky store for to see the great selection of educational tools and team gear we have to offer.

The post Year’s fastest sunsets happen around equinoxes first appeared on EarthSky.

from EarthSky https://ift.tt/S1B0DuL