Why carbon dioxide has such outsized influence on Earth’s climate

The Orbiting Carbon Observatory satellite makes precise measurements of Earth’s carbon dioxide levels from space. Image via NASA/JPL

By Jason West, University of North Carolina at Chapel Hill

I am often asked how carbon dioxide can have an important effect on global climate when its concentration is so small – just 0.041% of Earth’s atmosphere. And human activities are responsible for just 32% of that amount.

I study the importance of atmospheric gases for air pollution and climate change. The key to carbon dioxide’s strong influence on climate is its ability to absorb heat emitted from our planet’s surface, keeping it from escaping out to space.

The ‘Keeling Curve,’ named for scientist Charles David Keeling, tracks the accumulation of carbon dioxide in Earth’s atmosphere, measured in parts per million. Image via Scripps Institution of Oceanography.

Early greenhouse science

The scientists who first identified carbon dioxide’s importance for climate in the 1850s were also surprised by its influence. Working separately, John Tyndall in England and Eunice Foote in the United States found that carbon dioxide, water vapor and methane all absorbed heat, while more abundant gases did not.

Scientists had already calculated that the Earth was about 59 degrees Fahrenheit (33 degrees Celsius) warmer than it should be, given the amount of sunlight reaching its surface. The best explanation for that discrepancy was that the atmosphere retained heat to warm the planet.

Tyndall and Foote showed that nitrogen and oxygen, which together account for 99% of the atmosphere, had essentially no influence on Earth’s temperature because they did not absorb heat. Rather, they found that gases present in much smaller concentrations were entirely responsible for maintaining temperatures that made the Earth habitable, by trapping heat to create a natural greenhouse effect.

A blanket in the atmosphere

Earth constantly receives energy from the sun and radiates it back into space. For the planet’s temperature to remain constant, the net heat it receives from the sun must be balanced by outgoing heat that it gives off.

Since the sun is hot, it gives off energy in the form of shortwave radiation at mainly ultraviolet and visible wavelengths. Earth is much cooler, so it emits heat as infrared radiation, which has longer wavelengths.

The electromagnetic spectrum is the range of all types of EM radiation – energy that travels and spreads out as it goes. The sun is much hotter than the Earth, so it emits radiation at a higher energy level, which has a shorter wavelength. Image via NASA.

Carbon dioxide and other heat-trapping gases have molecular structures that enable them to absorb infrared radiation. The bonds between atoms in a molecule can vibrate in particular ways, like the pitch of a piano string. When the energy of a photon corresponds to the frequency of the molecule, it is absorbed and its energy transfers to the molecule.

Carbon dioxide and other heat-trapping gases have three or more atoms and frequencies that correspond to infrared radiation emitted by Earth. Oxygen and nitrogen, with just two atoms in their molecules, do not absorb infrared radiation.

Most incoming shortwave radiation from the sun passes through the atmosphere without being absorbed. But most outgoing infrared radiation is absorbed by heat-trapping gases in the atmosphere. Then they can release, or re-radiate, that heat. Some returns to Earth’s surface, keeping it warmer than it would be otherwise.

Earth receives solar energy from the sun (yellow), and returns energy back to space by reflecting some incoming light and radiating heat (red). Greenhouse gases trap some of that heat and return it to the planet’s surface. Image via NASA/Wikimedia.

Research on heat transmission

During the Cold War, the absorption of infrared radiation by many different gases was studied extensively. The work was led by the U.S. Air Force, which was developing heat-seeking missiles and needed to understand how to detect heat passing through air.

This research enabled scientists to understand the climate and atmospheric composition of all planets in the solar system by observing their infrared signatures. For example, Venus is about 870 F (470 C) because its thick atmosphere is 96.5% carbon dioxide.

It also informed weather forecast and climate models, allowing them to quantify how much infrared radiation is retained in the atmosphere and returned to Earth’s surface.

People sometimes ask me why carbon dioxide is important for climate, given that water vapor absorbs more infrared radiation and the two gases absorb at several of the same wavelengths. The reason is that Earth’s upper atmosphere controls the radiation that escapes to space. The upper atmosphere is much less dense and contains much less water vapor than near the ground, which means that adding more carbon dioxide significantly influences how much infrared radiation escapes to space.

Observing the greenhouse effect

Have you ever noticed that deserts are often colder at night than forests, even if their average temperatures are the same? Without much water vapor in the atmosphere over deserts, the radiation they give off escapes readily to space. In more humid regions radiation from the surface is trapped by water vapor in the air. Similarly, cloudy nights tend to be warmer than clear nights because more water vapor is present.

The influence of carbon dioxide can be seen in past changes in climate. Ice cores from over the past million years have shown that carbon dioxide concentrations were high during warm periods – about 0.028%. During ice ages, when the Earth was roughly 7 to 13 F (4-7 C) cooler than in the 20th century, carbon dioxide made up only about 0.018% of the atmosphere.

Even though water vapor is more important for the natural greenhouse effect, changes in carbon dioxide have driven past temperature changes. In contrast, water vapor levels in the atmosphere respond to temperature. As Earth becomes warmer, its atmosphere can hold more water vapor, which amplifies the initial warming in a process called the “water vapor feedback.” Variations in carbon dioxide have therefore been the controlling influence on past climate changes.

Small change, big effects

It shouldn’t be surprising that a small amount of carbon dioxide in the atmosphere can have a big effect. We take pills that are a tiny fraction of our body mass and expect them to affect us.

Today the level of carbon dioxide is higher than at any time in human history. Scientists widely agree that Earth’s average surface temperature has already increased by about 2 F (1 C) since the 1880s, and that human-caused increases in carbon dioxide and other heat-trapping gases are extremely likely to be responsible.

Without action to control emissions, carbon dioxide might reach 0.1% of the atmosphere by 2100, more than triple the level before the Industrial Revolution. This would be a faster change than transitions in Earth’s past that had huge consequences. Without action, this little sliver of the atmosphere will cause big problems.

Jason West, Professor of Environmental Sciences and Engineering, University of North Carolina at Chapel Hill

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Bottom line: An environmental scientist explains why carbon dioxide – CO2 – has such a big effect on Earth’s atmosphere and the greenhouse effect.

from EarthSky https://ift.tt/2NinRvO

The Orbiting Carbon Observatory satellite makes precise measurements of Earth’s carbon dioxide levels from space. Image via NASA/JPL

By Jason West, University of North Carolina at Chapel Hill

I am often asked how carbon dioxide can have an important effect on global climate when its concentration is so small – just 0.041% of Earth’s atmosphere. And human activities are responsible for just 32% of that amount.

I study the importance of atmospheric gases for air pollution and climate change. The key to carbon dioxide’s strong influence on climate is its ability to absorb heat emitted from our planet’s surface, keeping it from escaping out to space.

The ‘Keeling Curve,’ named for scientist Charles David Keeling, tracks the accumulation of carbon dioxide in Earth’s atmosphere, measured in parts per million. Image via Scripps Institution of Oceanography.

Early greenhouse science

The scientists who first identified carbon dioxide’s importance for climate in the 1850s were also surprised by its influence. Working separately, John Tyndall in England and Eunice Foote in the United States found that carbon dioxide, water vapor and methane all absorbed heat, while more abundant gases did not.

Scientists had already calculated that the Earth was about 59 degrees Fahrenheit (33 degrees Celsius) warmer than it should be, given the amount of sunlight reaching its surface. The best explanation for that discrepancy was that the atmosphere retained heat to warm the planet.

Tyndall and Foote showed that nitrogen and oxygen, which together account for 99% of the atmosphere, had essentially no influence on Earth’s temperature because they did not absorb heat. Rather, they found that gases present in much smaller concentrations were entirely responsible for maintaining temperatures that made the Earth habitable, by trapping heat to create a natural greenhouse effect.

A blanket in the atmosphere

Earth constantly receives energy from the sun and radiates it back into space. For the planet’s temperature to remain constant, the net heat it receives from the sun must be balanced by outgoing heat that it gives off.

Since the sun is hot, it gives off energy in the form of shortwave radiation at mainly ultraviolet and visible wavelengths. Earth is much cooler, so it emits heat as infrared radiation, which has longer wavelengths.

The electromagnetic spectrum is the range of all types of EM radiation – energy that travels and spreads out as it goes. The sun is much hotter than the Earth, so it emits radiation at a higher energy level, which has a shorter wavelength. Image via NASA.

Carbon dioxide and other heat-trapping gases have molecular structures that enable them to absorb infrared radiation. The bonds between atoms in a molecule can vibrate in particular ways, like the pitch of a piano string. When the energy of a photon corresponds to the frequency of the molecule, it is absorbed and its energy transfers to the molecule.

Carbon dioxide and other heat-trapping gases have three or more atoms and frequencies that correspond to infrared radiation emitted by Earth. Oxygen and nitrogen, with just two atoms in their molecules, do not absorb infrared radiation.

Most incoming shortwave radiation from the sun passes through the atmosphere without being absorbed. But most outgoing infrared radiation is absorbed by heat-trapping gases in the atmosphere. Then they can release, or re-radiate, that heat. Some returns to Earth’s surface, keeping it warmer than it would be otherwise.

Earth receives solar energy from the sun (yellow), and returns energy back to space by reflecting some incoming light and radiating heat (red). Greenhouse gases trap some of that heat and return it to the planet’s surface. Image via NASA/Wikimedia.

Research on heat transmission

During the Cold War, the absorption of infrared radiation by many different gases was studied extensively. The work was led by the U.S. Air Force, which was developing heat-seeking missiles and needed to understand how to detect heat passing through air.

This research enabled scientists to understand the climate and atmospheric composition of all planets in the solar system by observing their infrared signatures. For example, Venus is about 870 F (470 C) because its thick atmosphere is 96.5% carbon dioxide.

It also informed weather forecast and climate models, allowing them to quantify how much infrared radiation is retained in the atmosphere and returned to Earth’s surface.

People sometimes ask me why carbon dioxide is important for climate, given that water vapor absorbs more infrared radiation and the two gases absorb at several of the same wavelengths. The reason is that Earth’s upper atmosphere controls the radiation that escapes to space. The upper atmosphere is much less dense and contains much less water vapor than near the ground, which means that adding more carbon dioxide significantly influences how much infrared radiation escapes to space.

Observing the greenhouse effect

Have you ever noticed that deserts are often colder at night than forests, even if their average temperatures are the same? Without much water vapor in the atmosphere over deserts, the radiation they give off escapes readily to space. In more humid regions radiation from the surface is trapped by water vapor in the air. Similarly, cloudy nights tend to be warmer than clear nights because more water vapor is present.

The influence of carbon dioxide can be seen in past changes in climate. Ice cores from over the past million years have shown that carbon dioxide concentrations were high during warm periods – about 0.028%. During ice ages, when the Earth was roughly 7 to 13 F (4-7 C) cooler than in the 20th century, carbon dioxide made up only about 0.018% of the atmosphere.

Even though water vapor is more important for the natural greenhouse effect, changes in carbon dioxide have driven past temperature changes. In contrast, water vapor levels in the atmosphere respond to temperature. As Earth becomes warmer, its atmosphere can hold more water vapor, which amplifies the initial warming in a process called the “water vapor feedback.” Variations in carbon dioxide have therefore been the controlling influence on past climate changes.

Small change, big effects

It shouldn’t be surprising that a small amount of carbon dioxide in the atmosphere can have a big effect. We take pills that are a tiny fraction of our body mass and expect them to affect us.

Today the level of carbon dioxide is higher than at any time in human history. Scientists widely agree that Earth’s average surface temperature has already increased by about 2 F (1 C) since the 1880s, and that human-caused increases in carbon dioxide and other heat-trapping gases are extremely likely to be responsible.

Without action to control emissions, carbon dioxide might reach 0.1% of the atmosphere by 2100, more than triple the level before the Industrial Revolution. This would be a faster change than transitions in Earth’s past that had huge consequences. Without action, this little sliver of the atmosphere will cause big problems.

Jason West, Professor of Environmental Sciences and Engineering, University of North Carolina at Chapel Hill

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Bottom line: An environmental scientist explains why carbon dioxide – CO2 – has such a big effect on Earth’s atmosphere and the greenhouse effect.

from EarthSky https://ift.tt/2NinRvO

All you need to know: September equinox

First sunrise of fall from central North Carolina – September 22, 2018 – via our friend Lee Capps.

The September equinox will arrive on September 23, 2019 at 07:50 UTC. Although the equinox happens at the same moment worldwide, your clock time will depend on your time zone. For time zones in the continental U.S., this equinox comes early in the morning on September 23 (3:50 a.m. EDT, 2:50 a.m. CDT, 1:50 a.m. MDT and 12:50 a.m. PDT). Translate UTC to your time zone.

At the equinox, days and nights will be approximately equal in length. For us in the Northern Hemisphere, the sun is rising later now, and nightfall comes sooner. We’re enjoying the cooler days of almost-autumn.

Meanwhile, south of the equator, spring is about to begin.

Around the time of an equinox, Earth’s Northern and Southern Hemispheres are receiving the sun’s rays as equally as they can. Image via Wikipedia.

What is an equinox? The earliest humans spent more time outside than we do. They used the sky as both a clock and a calendar. They could easily see that the sun’s path across the sky, the length of daylight, and the location of the sunrise and sunset all shift in a regular way throughout the year.

Our ancestors built the first observatories to track the sun’s progress. One example is at Machu Picchu in Peru, where the Intihuatana stone, shown below, has been shown to be a precise indicator of the date of the two equinoxes and other significant celestial periods. The word Intihuatana, by the way, literally means for tying the sun.

The Intihuatana stone – also called the Hitching Post of the Sun – at Machu Picchu in Peru. It was used to track the sun throughout the year. Photo via Imagesofanthropology.com.

Today, we know each equinox and solstice is an astronomical event, caused by Earth’s tilt on its axis and ceaseless orbit around the sun.

Because Earth doesn’t orbit upright, but is instead tilted on its axis by 23 1/2 degrees, Earth’s Northern and Southern Hemispheres trade places throughout the year in receiving the sun’s light and warmth most directly.

We have an equinox twice a year – spring and fall – when the tilt of the Earth’s axis and Earth’s orbit around the sun combine in such a way that the axis is inclined neither away from nor toward the sun.

Earth’s two hemispheres are receiving the sun’s rays about equally around equinox-time. The sun is overhead at noon as seen from the equator. Night and day are approximately equal in length.

The name equinox comes from the Latin aequus (equal) and nox (night).

Of course, Earth never stops moving around the sun. So these days of approximately equal sunlight and night will change quickly.

Autumn in Sweden via EarthSky Facebook friend Jörgen Norrland Andersson.

Where should I look to see signs of the equinox in nature? The knowledge that summer is gone – and winter is coming – is everywhere now, on the northern half of Earth’s globe.

If you live in the Northern Hemisphere, you can easily notice the later dawns and earlier sunsets.

Also notice the arc of the sun across the sky each day. You’ll find it’s shifting toward the south. Birds and butterflies are migrating southward, too, along with the path of the sun.

The shorter days are bringing cooler weather. A chill is in the air. In New York City and other fashionable places, some people have stopped wearing white. Creatures of the wild are putting on their winter coats.

All around us, trees and plants are ending this year’s cycle of growth. Perhaps they are responding with glorious autumn leaves, or a last burst of bloom before winter comes.

In the night sky, Fomalhaut – the Autumn Star – is making its way across the heavens each night.

A first sunrise of autumn by EarthSky Facebook friend Mary C. Cox in North Carolina.

Does the sun rise due east and set due west at the equinox? Generally speaking, yes, it does. And that’s true no matter where you live on Earth, because we all see the same sky.

Everywhere on Earth, except at 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 line above the true equator of the Earth.

At the equinoxes, the sun appears overhead at noon as seen from Earth’s equator, as the illustration below shows.

Illustration of the sun’s location on the celestial equator, every hour, on the day of an equinox, via Tau’olunga/Wikimedia Commons.

That’s why the sun rises due east and sets due west for all of us. The sun is on the celestial equator, and the celestial equator intersects all of our horizons at points due east and due west.

This fact makes the day of an equinox a good day for finding due east and due west from your yard or other 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, long after Earth has moved on in its orbit around the sun, carrying the sunrise and sunset points southward.

Equinoxes and solstices. In each of the images, Earth’s rotational axis is perpendicular (straight up and down), with the North Pole at top and South Pole at bottom. Earth at the equinoxes shown at right; Earth at solstices shown at left. Images via Geosync.

Bottom line: Enjoy the 2019 equinox – a seasonal signpost in Earth’s orbit around the sun!

Equinox sun rises due east, sets due west

Why aren’t day and night exactly equal on the equinox?

Year’s fastest sunsets at equinox

Sun over Earth’s equator at equinox

from EarthSky https://ift.tt/304qjfE

First sunrise of fall from central North Carolina – September 22, 2018 – via our friend Lee Capps.

The September equinox will arrive on September 23, 2019 at 07:50 UTC. Although the equinox happens at the same moment worldwide, your clock time will depend on your time zone. For time zones in the continental U.S., this equinox comes early in the morning on September 23 (3:50 a.m. EDT, 2:50 a.m. CDT, 1:50 a.m. MDT and 12:50 a.m. PDT). Translate UTC to your time zone.

At the equinox, days and nights will be approximately equal in length. For us in the Northern Hemisphere, the sun is rising later now, and nightfall comes sooner. We’re enjoying the cooler days of almost-autumn.

Meanwhile, south of the equator, spring is about to begin.

Around the time of an equinox, Earth’s Northern and Southern Hemispheres are receiving the sun’s rays as equally as they can. Image via Wikipedia.

What is an equinox? The earliest humans spent more time outside than we do. They used the sky as both a clock and a calendar. They could easily see that the sun’s path across the sky, the length of daylight, and the location of the sunrise and sunset all shift in a regular way throughout the year.

Our ancestors built the first observatories to track the sun’s progress. One example is at Machu Picchu in Peru, where the Intihuatana stone, shown below, has been shown to be a precise indicator of the date of the two equinoxes and other significant celestial periods. The word Intihuatana, by the way, literally means for tying the sun.

The Intihuatana stone – also called the Hitching Post of the Sun – at Machu Picchu in Peru. It was used to track the sun throughout the year. Photo via Imagesofanthropology.com.

Today, we know each equinox and solstice is an astronomical event, caused by Earth’s tilt on its axis and ceaseless orbit around the sun.

Because Earth doesn’t orbit upright, but is instead tilted on its axis by 23 1/2 degrees, Earth’s Northern and Southern Hemispheres trade places throughout the year in receiving the sun’s light and warmth most directly.

We have an equinox twice a year – spring and fall – when the tilt of the Earth’s axis and Earth’s orbit around the sun combine in such a way that the axis is inclined neither away from nor toward the sun.

Earth’s two hemispheres are receiving the sun’s rays about equally around equinox-time. The sun is overhead at noon as seen from the equator. Night and day are approximately equal in length.

The name equinox comes from the Latin aequus (equal) and nox (night).

Of course, Earth never stops moving around the sun. So these days of approximately equal sunlight and night will change quickly.

Autumn in Sweden via EarthSky Facebook friend Jörgen Norrland Andersson.

Where should I look to see signs of the equinox in nature? The knowledge that summer is gone – and winter is coming – is everywhere now, on the northern half of Earth’s globe.

If you live in the Northern Hemisphere, you can easily notice the later dawns and earlier sunsets.

Also notice the arc of the sun across the sky each day. You’ll find it’s shifting toward the south. Birds and butterflies are migrating southward, too, along with the path of the sun.

The shorter days are bringing cooler weather. A chill is in the air. In New York City and other fashionable places, some people have stopped wearing white. Creatures of the wild are putting on their winter coats.

All around us, trees and plants are ending this year’s cycle of growth. Perhaps they are responding with glorious autumn leaves, or a last burst of bloom before winter comes.

In the night sky, Fomalhaut – the Autumn Star – is making its way across the heavens each night.

A first sunrise of autumn by EarthSky Facebook friend Mary C. Cox in North Carolina.

Does the sun rise due east and set due west at the equinox? Generally speaking, yes, it does. And that’s true no matter where you live on Earth, because we all see the same sky.

Everywhere on Earth, except at 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 line above the true equator of the Earth.

At the equinoxes, the sun appears overhead at noon as seen from Earth’s equator, as the illustration below shows.

Illustration of the sun’s location on the celestial equator, every hour, on the day of an equinox, via Tau’olunga/Wikimedia Commons.

That’s why the sun rises due east and sets due west for all of us. The sun is on the celestial equator, and the celestial equator intersects all of our horizons at points due east and due west.

This fact makes the day of an equinox a good day for finding due east and due west from your yard or other 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, long after Earth has moved on in its orbit around the sun, carrying the sunrise and sunset points southward.

Equinoxes and solstices. In each of the images, Earth’s rotational axis is perpendicular (straight up and down), with the North Pole at top and South Pole at bottom. Earth at the equinoxes shown at right; Earth at solstices shown at left. Images via Geosync.

Bottom line: Enjoy the 2019 equinox – a seasonal signpost in Earth’s orbit around the sun!

Equinox sun rises due east, sets due west

Why aren’t day and night exactly equal on the equinox?

Year’s fastest sunsets at equinox

Sun over Earth’s equator at equinox

from EarthSky https://ift.tt/304qjfE

Fomalhaut: The loneliest star

View larger. | Fomalhaut is sometimes called the Loneliest Star because no other bright stars shine near it in the sky. Photo by EarthSky Facebook friend Tony Gieracki. Thank you, Tony!

The star Fomalhaut is sometimes called the Autumn Star by people in the Northern Hemisphere, but it’s a spring star south of the equator. It’s famous in astronomical science as the first star with a visible exoplanet. It appears in a part of the sky that’s largely empty of bright stars. For this reason, in skylore, Fomalhaut is often called the Lonely One or Solitary One. It’s an easy star to spot and one you’ll want to meet.

How to see Fomalhaut. Fomalhaut – the 18th brightest star in the sky – is more or less opposite the sun in early September. And so it shines in the sky all night during the autumn months in the Northern Hemisphere (all night in spring for the Southern Hemisphere). In most years, finding Fomalhaut from latitudes like those in the U.S. is simple. Just face south in mid-evening in autumn and look. Fomalhaut is the brightest star in front of us on autumn evenings, as we face south. It’s typically less than a third of the way up in the sky (higher from far southern Texas or Florida, lower from more northerly locations).

From the Southern Hemisphere. Those at far southern latitudes on Earth see Fomalhaut high in their sky, for more of the year, than we do on the northern part of Earth. For your specific view, try Stellarium online.

For a larger view, and your specific view, see Stellarium online. | This chart shows the view southward around 9 p.m. in mid-September, from the Northern Hemisphere. In 2019, Fomalhaut has company. The 2 bright planets Jupiter and Saturn can be found near it in the sky.

In early September, Fomalhaut reaches its midnight culmination, meaning that it is highest in the sky to the south at local midnight. Finding Fomalhaut at the time it culminates is easiest, but this happens at different times on different dates. Here are just a few times and dates of culmination, but keep in mind that the times are only rough, although they are adjusted for daylight saving time as needed:

July 15, 4 a.m.
August 15, 1 a.m.
September 15, midnight
October 15, 10 p.m.
November 15 , 7 p.m.
December 15, 5 p.m.

Fomalhaut is part of the faint constellation Piscis Austrinus the Southern Fish. It’s part of a round pattern of stars, supposedly the open mouth of the Fish. But don’t expect to see a fish in these stars.

Fomalhaut is probably is the most southerly bright star that many North Americans know. Granted, a few bright stars farther to the south are visible from tropical and subtropic northern latitudes, but these brighter stars lurk near or beneath the horizon as seen as from middle and far northern latitudes in the Northern Hemisphere. Fomalhaut can be seen from as far north as 60 degrees latitude (southern Alaska, central Canada, northern Europe), where it just skims the southern horizon.

Fomalhaut lies in the constellation Piscis Austrinus the Southern Fish. Its name means Mouth of the Fish in Arabic. This irregular circle of stars – visible in a dark sky – represents the fish’s open mouth.

Another representation of Piscis Austrinus and its bright star Fomalhaut via Torsten Bronger/Wikimedia Commons.

Fomalhaut’s planet, Fomalhaut b or Dagon. The star Fomalhaut, which is known to be surrounded by several debris disks, holds a special place in the search for planets beyond our solar system. In 2008, scientists announced a visible planet for Fomalhaut. It was the first extrasolar planet visible to the eye in photographic images. In 2008, when astronomers made this announcement, we knew other planets were out there, orbiting distant suns. But, prior to the images of Fomalhaut b, all extrasolar planets, or exoplanets, made their presence known indirectly, for example, in some instances, by their gravitational tugging on their stars.

Fomalhaut’s planet was confirmed as real in 2012, from images taken with the Hubble Space Telescope (see the image below).

This planet – Fomalhaut b, recently given the name Dagon by the International Astronomical Union as part of its public process for giving proper names to exoplanets. Dagon was a Semitic deity that was half man and half fish.

The planet has a 1,700-year, highly elliptical orbit around its parent star. It has a periastron – that is, a closest point to its star – of 7.4 billion kilometers or 46 billion miles (~50 time the Earth-sun distance) and an apastron (farthest point from its star) of about 44 billion km or 27 billion miles (~300 the Earth-sun distance). According to Wikipedia – as of May 25, 2013 – Dagon is 110 Earth-sun distances from its parent star.

It should be mentioned that there was controversy surrounding the existence of Dagon for some years. You still sometimes see stories disputing that it exists.

View larger. | This false-color composite image, taken with the Hubble Space Telescope, reveals the orbital motion of the planet Fomalhaut b, aka Dagon. Based on these observations, astronomers calculated that the planet is in a 2,000-year-long, highly elliptical orbit. The planet will appear to cross a vast belt of debris around the star roughly 20 years from now. If the planet’s orbit lies in the same plane with the belt, icy and rocky debris in the belt could crash into the planet’s atmosphere and produce various phenomena. The black circle at the center of the image blocks out the light from the bright star, allowing reflected light from the belt and planet to be photographed. The Hubble images were taken with the Space Telescope Imaging Spectrograph in 2010 and 2012. Image via NASA/ ESA/ P. Kalas.

Fomalhaut in history and mythology. Fomalhaut is Alpha Piscis Austrinus (the brightest star in the Southern Fish), and the name Fomalhaut derives from the Arabic Fum al Hut, meaning Mouth of the Fish. Strangely, another Arabic title for the star means The First Frog.

In the sky visible from the Northern Hemisphere, the constellation Aquarius the Water Carrier resides above Fomalhaut’s constellation Piscis Austrinus. You can see a zig-zag line of stars that goes from Aquarius to Piscis Austrinus. In skylore, this line of stars represents water from the Jar of the Water Carrier, trickling into the open Mouth of the Fish, as shown in the illustration below.

According to Richard Hinckley Allen, Fomalhaut was one of the four guardians of the heavens to the ancient Persians, and given the name of Hastorang. (The other guardians were Aldebaran in Taurus, Antares in Scorpius, and Regulus in Leo.) Allen also says that Fomalhaut was a source of worship at the temple of Demeter at Eleusis in ancient Greece. In about 2500 B.C., Fomalhaut helped mark the location of the winter solstice, meaning that it helped to define the location in the sky where the sun crossed the meridian at noon on the first day of winter.

Water from the Water Jar of Aquarius can be seen going into the Mouth of the Southern Fish (located just off the bottom of this chart), in this depiction of these constellations from Urania’s Mirror, 1825. In the actual sky – if it’s dark where you are – you can easily see a zig-zag line of stars representing this flow of water. Chart via Wikimedia Commons.

The star Fomalhaut, and a word about the Main Sequence. As determined by an analysis of its light, Fomalhaut is classified as an A3V star. It’s considerably hotter and heavier than our sun. Imagine you could place our sun and Fomalhaut side by side in space – say, at 10 parsecs or 32.6 light-years away. In that case, Fomalhaut would outshine our sun in visible light by nearly 17 times. The “V” in Fomalhaut’s classification is called a luminosity class, and it designates the largest category of all, ordinary stars like our sun in the mature and stable part of their life spans.

These numbers and letters refer to what astronomers call the Main Sequence, a way of categorizing stars by mass and luminosity. The Main Sequence follows the rather odd progression of OBAFGKM. Os are the hottest and most massive stars, and Ms are the coolest and least massive stars. In addition, there is a numerical subdivision running from 0 to 9 with each letter. Our sun is a G2V, as is Alpha Centauri. Since Fomalhaut’s designation is significantly to the left of the sun’s in this sequence, you know it is hotter and more massive than our sun.

Fomalhaut’s actual distance from Earth, as determined by analysis of data from the Hipparcos mission, is 25 light-years. Fomalhaut’s mass and radius are, respectively, a little more than twice and a little less than twice solar values. Being hotter than the sun (about 8500 kelvins/8227 degrees Celsius or nearly 15,000 degrees F, compared to 10,000 degrees F or 5538 C for the sun), this star burns its fuel faster and has a shorter lifetime. In fact, it is estimated that Fomalhaut may have a lifespan of only about a billion years, a tenth of that of our cooler sun. Currently, Fomalhaut is likely less than halfway through its life.

Fomalhaut appears to the eye to be a single star like the sun, but there is another faint star a couple of degrees below (south of) Fomalhaut that is at about the same distance and moving through space in the same manner. This other star was recently found to be a companion to Fomalhaut, despite the fact that the two stars are separated by about a light-year. In 2013, researchers found that Fomalhaut is actually a triple star. It is one of the widest triple stars known. Read more about the third star in the Fomalhaut system.

Artist’s concept of what a planet orbiting Fomalhaut might have to endure as it plows through the dusty disk around this star. Image via NASA.

Fomalhaut’s position is RA: 22h 57m 39s, dec: -29° 37′ 19″.

Bottom line: Look for the star Fomalhaut in the constellation Piscis Austrinus the Southern Fish on Northern Hemisphere autumn evenings (Southern Hemisphere spring evenings). Because it’s the only bright star in its region of sky, Fomalhaut is sometimes called the Loneliest Star. This star is famous for its planet – Fomalhaut b, now called Dagon – which was the first visible extrasolar planet.

from EarthSky https://ift.tt/34QpJl1

View larger. | Fomalhaut is sometimes called the Loneliest Star because no other bright stars shine near it in the sky. Photo by EarthSky Facebook friend Tony Gieracki. Thank you, Tony!

The star Fomalhaut is sometimes called the Autumn Star by people in the Northern Hemisphere, but it’s a spring star south of the equator. It’s famous in astronomical science as the first star with a visible exoplanet. It appears in a part of the sky that’s largely empty of bright stars. For this reason, in skylore, Fomalhaut is often called the Lonely One or Solitary One. It’s an easy star to spot and one you’ll want to meet.

How to see Fomalhaut. Fomalhaut – the 18th brightest star in the sky – is more or less opposite the sun in early September. And so it shines in the sky all night during the autumn months in the Northern Hemisphere (all night in spring for the Southern Hemisphere). In most years, finding Fomalhaut from latitudes like those in the U.S. is simple. Just face south in mid-evening in autumn and look. Fomalhaut is the brightest star in front of us on autumn evenings, as we face south. It’s typically less than a third of the way up in the sky (higher from far southern Texas or Florida, lower from more northerly locations).

From the Southern Hemisphere. Those at far southern latitudes on Earth see Fomalhaut high in their sky, for more of the year, than we do on the northern part of Earth. For your specific view, try Stellarium online.

For a larger view, and your specific view, see Stellarium online. | This chart shows the view southward around 9 p.m. in mid-September, from the Northern Hemisphere. In 2019, Fomalhaut has company. The 2 bright planets Jupiter and Saturn can be found near it in the sky.

In early September, Fomalhaut reaches its midnight culmination, meaning that it is highest in the sky to the south at local midnight. Finding Fomalhaut at the time it culminates is easiest, but this happens at different times on different dates. Here are just a few times and dates of culmination, but keep in mind that the times are only rough, although they are adjusted for daylight saving time as needed:

July 15, 4 a.m.
August 15, 1 a.m.
September 15, midnight
October 15, 10 p.m.
November 15 , 7 p.m.
December 15, 5 p.m.

Fomalhaut is part of the faint constellation Piscis Austrinus the Southern Fish. It’s part of a round pattern of stars, supposedly the open mouth of the Fish. But don’t expect to see a fish in these stars.

Fomalhaut is probably is the most southerly bright star that many North Americans know. Granted, a few bright stars farther to the south are visible from tropical and subtropic northern latitudes, but these brighter stars lurk near or beneath the horizon as seen as from middle and far northern latitudes in the Northern Hemisphere. Fomalhaut can be seen from as far north as 60 degrees latitude (southern Alaska, central Canada, northern Europe), where it just skims the southern horizon.

Fomalhaut lies in the constellation Piscis Austrinus the Southern Fish. Its name means Mouth of the Fish in Arabic. This irregular circle of stars – visible in a dark sky – represents the fish’s open mouth.

Another representation of Piscis Austrinus and its bright star Fomalhaut via Torsten Bronger/Wikimedia Commons.

Fomalhaut’s planet, Fomalhaut b or Dagon. The star Fomalhaut, which is known to be surrounded by several debris disks, holds a special place in the search for planets beyond our solar system. In 2008, scientists announced a visible planet for Fomalhaut. It was the first extrasolar planet visible to the eye in photographic images. In 2008, when astronomers made this announcement, we knew other planets were out there, orbiting distant suns. But, prior to the images of Fomalhaut b, all extrasolar planets, or exoplanets, made their presence known indirectly, for example, in some instances, by their gravitational tugging on their stars.

Fomalhaut’s planet was confirmed as real in 2012, from images taken with the Hubble Space Telescope (see the image below).

This planet – Fomalhaut b, recently given the name Dagon by the International Astronomical Union as part of its public process for giving proper names to exoplanets. Dagon was a Semitic deity that was half man and half fish.

The planet has a 1,700-year, highly elliptical orbit around its parent star. It has a periastron – that is, a closest point to its star – of 7.4 billion kilometers or 46 billion miles (~50 time the Earth-sun distance) and an apastron (farthest point from its star) of about 44 billion km or 27 billion miles (~300 the Earth-sun distance). According to Wikipedia – as of May 25, 2013 – Dagon is 110 Earth-sun distances from its parent star.

It should be mentioned that there was controversy surrounding the existence of Dagon for some years. You still sometimes see stories disputing that it exists.

View larger. | This false-color composite image, taken with the Hubble Space Telescope, reveals the orbital motion of the planet Fomalhaut b, aka Dagon. Based on these observations, astronomers calculated that the planet is in a 2,000-year-long, highly elliptical orbit. The planet will appear to cross a vast belt of debris around the star roughly 20 years from now. If the planet’s orbit lies in the same plane with the belt, icy and rocky debris in the belt could crash into the planet’s atmosphere and produce various phenomena. The black circle at the center of the image blocks out the light from the bright star, allowing reflected light from the belt and planet to be photographed. The Hubble images were taken with the Space Telescope Imaging Spectrograph in 2010 and 2012. Image via NASA/ ESA/ P. Kalas.

Fomalhaut in history and mythology. Fomalhaut is Alpha Piscis Austrinus (the brightest star in the Southern Fish), and the name Fomalhaut derives from the Arabic Fum al Hut, meaning Mouth of the Fish. Strangely, another Arabic title for the star means The First Frog.

In the sky visible from the Northern Hemisphere, the constellation Aquarius the Water Carrier resides above Fomalhaut’s constellation Piscis Austrinus. You can see a zig-zag line of stars that goes from Aquarius to Piscis Austrinus. In skylore, this line of stars represents water from the Jar of the Water Carrier, trickling into the open Mouth of the Fish, as shown in the illustration below.

According to Richard Hinckley Allen, Fomalhaut was one of the four guardians of the heavens to the ancient Persians, and given the name of Hastorang. (The other guardians were Aldebaran in Taurus, Antares in Scorpius, and Regulus in Leo.) Allen also says that Fomalhaut was a source of worship at the temple of Demeter at Eleusis in ancient Greece. In about 2500 B.C., Fomalhaut helped mark the location of the winter solstice, meaning that it helped to define the location in the sky where the sun crossed the meridian at noon on the first day of winter.

Water from the Water Jar of Aquarius can be seen going into the Mouth of the Southern Fish (located just off the bottom of this chart), in this depiction of these constellations from Urania’s Mirror, 1825. In the actual sky – if it’s dark where you are – you can easily see a zig-zag line of stars representing this flow of water. Chart via Wikimedia Commons.

The star Fomalhaut, and a word about the Main Sequence. As determined by an analysis of its light, Fomalhaut is classified as an A3V star. It’s considerably hotter and heavier than our sun. Imagine you could place our sun and Fomalhaut side by side in space – say, at 10 parsecs or 32.6 light-years away. In that case, Fomalhaut would outshine our sun in visible light by nearly 17 times. The “V” in Fomalhaut’s classification is called a luminosity class, and it designates the largest category of all, ordinary stars like our sun in the mature and stable part of their life spans.

These numbers and letters refer to what astronomers call the Main Sequence, a way of categorizing stars by mass and luminosity. The Main Sequence follows the rather odd progression of OBAFGKM. Os are the hottest and most massive stars, and Ms are the coolest and least massive stars. In addition, there is a numerical subdivision running from 0 to 9 with each letter. Our sun is a G2V, as is Alpha Centauri. Since Fomalhaut’s designation is significantly to the left of the sun’s in this sequence, you know it is hotter and more massive than our sun.

Fomalhaut’s actual distance from Earth, as determined by analysis of data from the Hipparcos mission, is 25 light-years. Fomalhaut’s mass and radius are, respectively, a little more than twice and a little less than twice solar values. Being hotter than the sun (about 8500 kelvins/8227 degrees Celsius or nearly 15,000 degrees F, compared to 10,000 degrees F or 5538 C for the sun), this star burns its fuel faster and has a shorter lifetime. In fact, it is estimated that Fomalhaut may have a lifespan of only about a billion years, a tenth of that of our cooler sun. Currently, Fomalhaut is likely less than halfway through its life.

Fomalhaut appears to the eye to be a single star like the sun, but there is another faint star a couple of degrees below (south of) Fomalhaut that is at about the same distance and moving through space in the same manner. This other star was recently found to be a companion to Fomalhaut, despite the fact that the two stars are separated by about a light-year. In 2013, researchers found that Fomalhaut is actually a triple star. It is one of the widest triple stars known. Read more about the third star in the Fomalhaut system.

Artist’s concept of what a planet orbiting Fomalhaut might have to endure as it plows through the dusty disk around this star. Image via NASA.

Fomalhaut’s position is RA: 22h 57m 39s, dec: -29° 37′ 19″.

Bottom line: Look for the star Fomalhaut in the constellation Piscis Austrinus the Southern Fish on Northern Hemisphere autumn evenings (Southern Hemisphere spring evenings). Because it’s the only bright star in its region of sky, Fomalhaut is sometimes called the Loneliest Star. This star is famous for its planet – Fomalhaut b, now called Dagon – which was the first visible extrasolar planet.

from EarthSky https://ift.tt/34QpJl1

2019 SkS Weekly Climate Change & Global Warming Digest #37

Story of the Week... Editorial of the Week... Toon of the Week... Coming Soon on SkS... Climate Feedback Reviews... SkS Week in Review... Poster of the Week...

Story of the Week...

'Going to the streets again': what you need to know about Friday's climate strike

Organisers expect a stronger presence from unions, workers and companies as student activists reach out to adults

Australian school students are set to walk out of classrooms again to call for climate action as part of a global strike three days before a UN summit. Photograph: Dan Peled/AAP

Thousands of Australian school students are again preparing to walk out of classrooms across the country to demand action on the climate crisis.

The global mass day of action will take place on Friday 20 September, three days before the United Nations climate summit in New York.

It follows strikes in March this year in which 150,000 people marched in Australia and 1.5 million took part worldwide.

Organisers expect next week’s global strikes will be bigger and, this time there will be a much stronger presence from unions, workers and companies that have signed up to strike in solidarity with the young activists.

Here’s a guide to what’s happening.

'Going to the streets again': what you need to know about Friday's climate strike by Lisa Cox, Environment, Guardian, Sep 14, 2019

Click here to access the entire article as posted on the Guardian website.

---

Editorial of the Week...

Can we please base our climate change discussions on facts?

One flawed assumption about global warming is that nuclear power has to be part of the solution. (Allen J. Schaben / Los Angeles Times)

In the debate about global warming, as last week’s climate change town hall on CNN made clear, policy discussions are often based on false premises. In Thursday’s debate, the Democratic presidential candidates will again discuss climate issues. Here are a few faulty assumptions they should reject.

One oft-repeated canard is that we won’t be able to reach zero net carbon dioxide emissions without re-embracing nuclear power. Several candidates responded to this claim last week by saying they could not support nuclear power because it was too expensive and we haven’t solved the waste disposal problem. Both those things are true, but they leave a crucial point out of the discussion.

If it were really the case that we couldn’t meet our energy needs without nuclear power, then we could certainly suck up the cost (currently about double that of solar, and as much as three times that of wind) and get back to work on waste disposal. But the assertion that we can’t decarbonize the energy system without additional nuclear power is flawed.

Can we please base our climate change discussions on facts?, Opinion by Naomi Oreskes, Los Angeles Times, Sep 12, 2019

Click here to access the entire Op-ed as published on the Los Angeles Times website.

---

Toon of the Week...

 

---

Coming Soon on SkS...

• Skeptical Science New Research for Week #36, 2019 (Doug Bostrom)
• Climate change and food (Yale Climate Connections)
• Skeptical Science to join the Global Climate Strike (Baerbel)
• The Consensus Handbook: Download and (German) translation (Baerbel)
• 2019 SkS Weekly Climate Change & Global Warming News Roundup #38 (John Hartz)
• 2019 SkS Weekly Climate Change & Global Warming Digest #38 (John Hartz) 

---

Climate Feedback Reviews...

[To be added.] 

---

Poster of the Week...

 

---

SkS Week in Review... 

• 2019 SkS Weekly Climate Change & Global Warming News Roundup #37 by John Hartz
• Climate denier scientists think these 5 arguments will persuade EU and UN leaders by Dana Nuccitelli
• Skeptical Science New Research for Week #36, 2019 by Doug Bostrom
• Key facts about the new EPA plan to reverse the Obama-era methane leaks rule by Dana Nuccitelli (Yale Climate Connection)
• 2019 SkS Weekly Climate Change & Global Warming Digest #36 by John Hartz

 

from Skeptical Science https://ift.tt/305YzrW

Story of the Week... Editorial of the Week... Toon of the Week... Coming Soon on SkS... Climate Feedback Reviews... SkS Week in Review... Poster of the Week...

Story of the Week...

'Going to the streets again': what you need to know about Friday's climate strike

Organisers expect a stronger presence from unions, workers and companies as student activists reach out to adults

Australian school students are set to walk out of classrooms again to call for climate action as part of a global strike three days before a UN summit. Photograph: Dan Peled/AAP

Thousands of Australian school students are again preparing to walk out of classrooms across the country to demand action on the climate crisis.

The global mass day of action will take place on Friday 20 September, three days before the United Nations climate summit in New York.

It follows strikes in March this year in which 150,000 people marched in Australia and 1.5 million took part worldwide.

Organisers expect next week’s global strikes will be bigger and, this time there will be a much stronger presence from unions, workers and companies that have signed up to strike in solidarity with the young activists.

Here’s a guide to what’s happening.

'Going to the streets again': what you need to know about Friday's climate strike by Lisa Cox, Environment, Guardian, Sep 14, 2019

Click here to access the entire article as posted on the Guardian website.

---

Editorial of the Week...

Can we please base our climate change discussions on facts?

One flawed assumption about global warming is that nuclear power has to be part of the solution. (Allen J. Schaben / Los Angeles Times)

In the debate about global warming, as last week’s climate change town hall on CNN made clear, policy discussions are often based on false premises. In Thursday’s debate, the Democratic presidential candidates will again discuss climate issues. Here are a few faulty assumptions they should reject.

One oft-repeated canard is that we won’t be able to reach zero net carbon dioxide emissions without re-embracing nuclear power. Several candidates responded to this claim last week by saying they could not support nuclear power because it was too expensive and we haven’t solved the waste disposal problem. Both those things are true, but they leave a crucial point out of the discussion.

If it were really the case that we couldn’t meet our energy needs without nuclear power, then we could certainly suck up the cost (currently about double that of solar, and as much as three times that of wind) and get back to work on waste disposal. But the assertion that we can’t decarbonize the energy system without additional nuclear power is flawed.

Can we please base our climate change discussions on facts?, Opinion by Naomi Oreskes, Los Angeles Times, Sep 12, 2019

Click here to access the entire Op-ed as published on the Los Angeles Times website.

---

Toon of the Week...

 

---

Coming Soon on SkS...

• Skeptical Science New Research for Week #36, 2019 (Doug Bostrom)
• Climate change and food (Yale Climate Connections)
• Skeptical Science to join the Global Climate Strike (Baerbel)
• The Consensus Handbook: Download and (German) translation (Baerbel)
• 2019 SkS Weekly Climate Change & Global Warming News Roundup #38 (John Hartz)
• 2019 SkS Weekly Climate Change & Global Warming Digest #38 (John Hartz) 

---

Climate Feedback Reviews...

[To be added.] 

---

Poster of the Week...

 

---

SkS Week in Review... 

• 2019 SkS Weekly Climate Change & Global Warming News Roundup #37 by John Hartz
• Climate denier scientists think these 5 arguments will persuade EU and UN leaders by Dana Nuccitelli
• Skeptical Science New Research for Week #36, 2019 by Doug Bostrom
• Key facts about the new EPA plan to reverse the Obama-era methane leaks rule by Dana Nuccitelli (Yale Climate Connection)
• 2019 SkS Weekly Climate Change & Global Warming Digest #36 by John Hartz

 

from Skeptical Science https://ift.tt/305YzrW

Sub auroral arc over Peyto Lake, Alberta

View larger on Flickr. | Auroral arc panorama (STEVE) from Christy Turner Photography. Used with permission.

Christy Turner posted this amazing arc on Flickr on September 10, while reminding us that STEVE stands for Strong Thermal Emission Velocity Enhancement. In this photo, the arc appears with the northern lights, and, as Christy writes, it’s:

…a very cool phenomenon!

This series of photos I shot have been published as a co-author in the Journal of Geophysical Research Letters, Space Physics in collaboration with Dr. Stephen Mende at UC Berkeley, thereby contributing to space weather research! Exciting use for my photos! I continue to do active data collection for Berkeley.

agupubs.onlinelibrary.wiley.com/toc/21699402/2019/124/7

I shoot with Tamron lenses, in this case Tamron 15-30F2.8

Follow more of my internationally published aurora borealis work and more here:
www.facebook.com/christyturnerphotography

Thank for allowing us to publish your photo, Christy!

Read Christy’s blog post on chasing sub auroral arcs

Bottom line: Sub auroral arc (STEVE) with the northern lights over Peyto Lake, Alberta.

from EarthSky https://ift.tt/30lIXeQ

View larger on Flickr. | Auroral arc panorama (STEVE) from Christy Turner Photography. Used with permission.

Christy Turner posted this amazing arc on Flickr on September 10, while reminding us that STEVE stands for Strong Thermal Emission Velocity Enhancement. In this photo, the arc appears with the northern lights, and, as Christy writes, it’s:

…a very cool phenomenon!

This series of photos I shot have been published as a co-author in the Journal of Geophysical Research Letters, Space Physics in collaboration with Dr. Stephen Mende at UC Berkeley, thereby contributing to space weather research! Exciting use for my photos! I continue to do active data collection for Berkeley.

agupubs.onlinelibrary.wiley.com/toc/21699402/2019/124/7

I shoot with Tamron lenses, in this case Tamron 15-30F2.8

Follow more of my internationally published aurora borealis work and more here:
www.facebook.com/christyturnerphotography

Thank for allowing us to publish your photo, Christy!

Read Christy’s blog post on chasing sub auroral arcs

Bottom line: Sub auroral arc (STEVE) with the northern lights over Peyto Lake, Alberta.

from EarthSky https://ift.tt/30lIXeQ

Milky Way’s black hole appears to be getting hungrier

Artist’s concept of an object called S0-2 orbiting our Milky Way’s supermassive black hole. Astronomers tracked this object for years, hoping to catch it falling over the hole’s event horizon. It did not fall in, but its close approach in 2018 might be one reason for the black hole’s growing appetite now. Image via Nicolle Fuller/National Science Foundation.

UCLA astronomers announced on September 11, 2019, that, last May, they caught the supermassive black hole at the center of our Milky Way galaxy having an unusually large meal of interstellar gas and dust. They caught the feast on May 13 (although of course it happened some 25,000 years ago earlier, since the center of the galaxy is about 25,000 light-years away). What they saw was this. The black hole – called Sagittarius A*, pronounced Sagittarius A-star – became extremely bright in May 2019, growing 75 times as bright for a few hours. Yet, as of now, the researchers don’t yet understand why. Why did the area just outside the black hole’s event horizon – its point of no return – suddenly become brighter? What did it ingest, and why at that time?

Astronomer Tuan Do is lead author of new research describing this event, published September 11 in Astrophysical Journal Letters. He also produced the timelapse in the tweet below, which depicts the brightness changes at Sgr A*. Andrea Ghez, of the UCLA Galactic Center Group, is co-senior author on the new paper. She said:

We have never seen anything like this in the 24 years we have studied the supermassive black hole. It’s usually a pretty quiet, wimpy black hole on a diet. We don’t know what is driving this big feast.

In a statement, the researchers also said they:

… analyzed more than 13,000 observations of the black hole from 133 nights since 2003. The images were gathered by the W. M. Keck Observatory in Hawaii and the European Southern Observatory’s Very Large Telescope in Chile. The team found that on May 13, the area just outside the black hole’s ‘point of no return’ (so called because once matter enters, it can never escape) was twice as bright as the next-brightest observation.

They observed large changes on two other nights this year; all three of those changes were ‘unprecedented,’ Ghez said.

They said the brightness surrounding the black hole always varies somewhat, but the extreme variations in brightness observed this year left them “stunned.”

So what is going on?

In an absolute sense, the increased brightness on a few nights in 2019 can be explained by radiation from gas and dust falling into the black hole. One hypothesis about the increased activity is that when a star called S0-2 made its closest approach to the black hole during the summer 2018, it launched a large quantity of gas that reached the black hole this year. Tuan Do, the study’s lead author, said:

The first image I saw that night, the black hole was so bright I initially mistook it for the star S0-2, because I had never seen Sagittarius A* that bright. But it quickly became clear the source had to be the black hole, which was really exciting.

Another possibility involves a bizarre object known as G2, which is most likely a pair of binary stars, which made its closest approach to the black hole in 2014. It’s possible the black hole could have stripped off the outer layer of G2, Ghez said, which could help explain the increased brightness just outside the black hole.

Morris said another possibility is that the brightening corresponds to the demise of large asteroids that have been drawn in to the black hole.

Here's a timelapse of images over 2.5 hr from May from @keckobservatory of the supermassive black hole Sgr A*. The black hole is always variable, but this was the brightest we’ve seen in the infrared so far. It was probably even brighter before we started observing that night! pic.twitter.com/MwXioZ7twV

– Tuan Do (@quantumpenguin) August 11, 2019

The question for astronomers is, what does this activity mean? Is it simply an extraordinary singular event, or is it a precursor to significantly increased activity for Sgr A*? Mark Morris, UCLA professor of physics and astronomy, is another author on the paper. He said:

The big question is whether the black hole is entering a new phase – for example if the spigot has been turned up and the rate of gas falling down the black hole ‘drain’ has increased for an extended period – or whether we have just seen the fireworks from a few unusual blobs of gas falling in.

The team has continued to observe the area. They say they’ll try to settle the question based on what they see from new images. Ghez said:

We want to know how black holes grow and affect the evolution of galaxies and the universe. We want to know why the supermassive hole gets brighter and how it gets brighter.

By the way, these astronomers commented:

The black hole is some 26,000 light-years away and poses no danger to our planet. Do said the radiation would have to be 10 billion times as bright as what the astronomers detected to affect life on Earth.

Astrophysical Journal Letters also published a second article by the researchers, describing speckle holography, the technique that enabled them to extract and use very faint information from 24 years of data they recorded from near the black hole.

Ghez’s research team reported July 25 in the journal Science the most comprehensive test of Einstein’s iconic general theory of relativity near the black hole. Their conclusion that Einstein’s theory passed the test and is correct, at least for now, was based on their study of S0-2 as it made a complete orbit around the black hole.

Ghez’s team said it:

… studies more than 3,000 stars that orbit the supermassive black hole. Since 2004, the scientists have used a powerful technology that Ghez helped pioneer, called adaptive optics, which corrects the distorting effects of the Earth’s atmosphere in real time. But speckle holography enabled the researchers to improve the data from the decade before adaptive optics came into play. Reanalyzing data from those years helped the team conclude that they had not seen that level of brightness near the black hole in 24 years.

Ghez said:

It was like doing LASIK surgery on our early images. We collected the data to answer one question and serendipitously unveiled other exciting scientific discoveries that we didn’t anticipate.

Twitter Talk: Flashing Supermassive Black Hole from Keck Observatory on Vimeo.

Bottom line: UCLA astronomers announced on September 11, 2019, that – in May – they caught the supermassive black hole at the center of our Milky Way galaxy having an unusually large meal of interstellar gas and dust. Why did the area just outside the black hole’s event horizon – its point of no return – suddenly become dramatically brighter? What did it ingest, and why at that time?

Source: Unprecedented Near-infrared Brightness and Variability of Sgr A*

Via UCLA

from EarthSky https://ift.tt/30jb3aL

Artist’s concept of an object called S0-2 orbiting our Milky Way’s supermassive black hole. Astronomers tracked this object for years, hoping to catch it falling over the hole’s event horizon. It did not fall in, but its close approach in 2018 might be one reason for the black hole’s growing appetite now. Image via Nicolle Fuller/National Science Foundation.

UCLA astronomers announced on September 11, 2019, that, last May, they caught the supermassive black hole at the center of our Milky Way galaxy having an unusually large meal of interstellar gas and dust. They caught the feast on May 13 (although of course it happened some 25,000 years ago earlier, since the center of the galaxy is about 25,000 light-years away). What they saw was this. The black hole – called Sagittarius A*, pronounced Sagittarius A-star – became extremely bright in May 2019, growing 75 times as bright for a few hours. Yet, as of now, the researchers don’t yet understand why. Why did the area just outside the black hole’s event horizon – its point of no return – suddenly become brighter? What did it ingest, and why at that time?

Astronomer Tuan Do is lead author of new research describing this event, published September 11 in Astrophysical Journal Letters. He also produced the timelapse in the tweet below, which depicts the brightness changes at Sgr A*. Andrea Ghez, of the UCLA Galactic Center Group, is co-senior author on the new paper. She said:

We have never seen anything like this in the 24 years we have studied the supermassive black hole. It’s usually a pretty quiet, wimpy black hole on a diet. We don’t know what is driving this big feast.

In a statement, the researchers also said they:

… analyzed more than 13,000 observations of the black hole from 133 nights since 2003. The images were gathered by the W. M. Keck Observatory in Hawaii and the European Southern Observatory’s Very Large Telescope in Chile. The team found that on May 13, the area just outside the black hole’s ‘point of no return’ (so called because once matter enters, it can never escape) was twice as bright as the next-brightest observation.

They observed large changes on two other nights this year; all three of those changes were ‘unprecedented,’ Ghez said.

They said the brightness surrounding the black hole always varies somewhat, but the extreme variations in brightness observed this year left them “stunned.”

So what is going on?

In an absolute sense, the increased brightness on a few nights in 2019 can be explained by radiation from gas and dust falling into the black hole. One hypothesis about the increased activity is that when a star called S0-2 made its closest approach to the black hole during the summer 2018, it launched a large quantity of gas that reached the black hole this year. Tuan Do, the study’s lead author, said:

The first image I saw that night, the black hole was so bright I initially mistook it for the star S0-2, because I had never seen Sagittarius A* that bright. But it quickly became clear the source had to be the black hole, which was really exciting.

Another possibility involves a bizarre object known as G2, which is most likely a pair of binary stars, which made its closest approach to the black hole in 2014. It’s possible the black hole could have stripped off the outer layer of G2, Ghez said, which could help explain the increased brightness just outside the black hole.

Morris said another possibility is that the brightening corresponds to the demise of large asteroids that have been drawn in to the black hole.

Here's a timelapse of images over 2.5 hr from May from @keckobservatory of the supermassive black hole Sgr A*. The black hole is always variable, but this was the brightest we’ve seen in the infrared so far. It was probably even brighter before we started observing that night! pic.twitter.com/MwXioZ7twV

– Tuan Do (@quantumpenguin) August 11, 2019

The question for astronomers is, what does this activity mean? Is it simply an extraordinary singular event, or is it a precursor to significantly increased activity for Sgr A*? Mark Morris, UCLA professor of physics and astronomy, is another author on the paper. He said:

The big question is whether the black hole is entering a new phase – for example if the spigot has been turned up and the rate of gas falling down the black hole ‘drain’ has increased for an extended period – or whether we have just seen the fireworks from a few unusual blobs of gas falling in.

The team has continued to observe the area. They say they’ll try to settle the question based on what they see from new images. Ghez said:

We want to know how black holes grow and affect the evolution of galaxies and the universe. We want to know why the supermassive hole gets brighter and how it gets brighter.

By the way, these astronomers commented:

The black hole is some 26,000 light-years away and poses no danger to our planet. Do said the radiation would have to be 10 billion times as bright as what the astronomers detected to affect life on Earth.

Astrophysical Journal Letters also published a second article by the researchers, describing speckle holography, the technique that enabled them to extract and use very faint information from 24 years of data they recorded from near the black hole.

Ghez’s research team reported July 25 in the journal Science the most comprehensive test of Einstein’s iconic general theory of relativity near the black hole. Their conclusion that Einstein’s theory passed the test and is correct, at least for now, was based on their study of S0-2 as it made a complete orbit around the black hole.

Ghez’s team said it:

… studies more than 3,000 stars that orbit the supermassive black hole. Since 2004, the scientists have used a powerful technology that Ghez helped pioneer, called adaptive optics, which corrects the distorting effects of the Earth’s atmosphere in real time. But speckle holography enabled the researchers to improve the data from the decade before adaptive optics came into play. Reanalyzing data from those years helped the team conclude that they had not seen that level of brightness near the black hole in 24 years.

Ghez said:

It was like doing LASIK surgery on our early images. We collected the data to answer one question and serendipitously unveiled other exciting scientific discoveries that we didn’t anticipate.

Twitter Talk: Flashing Supermassive Black Hole from Keck Observatory on Vimeo.

Bottom line: UCLA astronomers announced on September 11, 2019, that – in May – they caught the supermassive black hole at the center of our Milky Way galaxy having an unusually large meal of interstellar gas and dust. Why did the area just outside the black hole’s event horizon – its point of no return – suddenly become dramatically brighter? What did it ingest, and why at that time?

Source: Unprecedented Near-infrared Brightness and Variability of Sgr A*

Via UCLA

from EarthSky https://ift.tt/30jb3aL

Is K2-18b really a habitable super-Earth?

Artist’s concept of K2-18b, as well as another planet in this system, K2-18c, with the parent star, a red dwarf, in the background. Image via Alex Boersma/iREx.

A couple of days ago, EarthSky reported that for the first time ever, water vapor had been detected in the atmosphere of a potentially habitable super-Earth exoplanet. We weren’t alone in our report. As might be expected, the finding received a lot of attention from media. But, it turns out, that the story might not be quite as first reported and was mis-characterized to some extent.

The discovery was outlined in two different papers, the first one published on ArXiv on September 10, 2019 and the second in Nature Astronomy on September 11, 2019.

The papers detail the finding of water vapor in the atmosphere of K2-18b, an exoplanet in the habitable zone of its star – where temperatures could allow liquid water to exist – 110 light-years from Earth. It’s accurate that this is the first time that water vapor has been identified in the atmosphere of a smaller exoplanet (non-gas-giant) in the habitable zone of its star, but soon after the announcement, many planetary scientists critiqued how the discovery was covered in media and social media.

The water vapor detection itself is confirmed, but there is a lot of debate as to just what kind of planet K2-18b actually is, and how habitable it may be (or not).

Another artist’s concept of super-Earth K2-18b. Scientists have detected water vapor in its atmosphere, but is it habitable? Most scientists say it’s unlikely. Image via ESA/Hubble, M. Kornmesser/UCL News.

Some scientists, including in the Nature Astronomy paper, have referred to the planet as a super-Earth. A super-Earth is larger than Earth but smaller than Neptune – typically up to about a maximum of twice the size of Earth – and many have been discovered already. Most are thought to be rocky, like Earth, but there is a transition point – starting about 1.6 – two times Earth’s radius – where a planet can become a mini-gas-giant, or a mini-Neptune as they are usually called. They are larger than super-Earths, but still smaller than Neptune. Most scientists now consider K2-18b to be a mini-Neptune, not a super-Earth, with a deep atmosphere of hydrogen and/or helium, and possibly no solid surface at all.

K2-18b has a radius of about 2.7 times that of Earth, and a mass about nine times that of Earth. While some scientists would still consider that to be a possible super-Earth, most it seems would classify it as a mini-Neptune. All of this can be a bit confusing.

The 2017 study previously linked to considered that K2-18b might be either large and rocky or covered with water and/or ice. But that study didn’t account for atmospheric constraints, only mass and radius. As exoplanet scientist Erin May told me on Twitter:

My PhD partially focused on the distinction between these classes of planets. Many studies show that it’s extremely difficult to make a planet > than 2 Earth-radii without a large atmosphere. Mass & radius (density) alone are actually not very useful here. I’d also like to point out that from mass and radius alone, this planet should have never been considered a super-Earth. I think there’s a tendency to throw this term around because it’s more “exciting”, but we as astronomers need to keep our terminology straight.

Néstor Espinoza, an astronomer at the Max Planck Institute for Astronomy (MPIA), also told me:

If you believe the water feature, you have to believe it is an H/He dominated atmosphere so yes. And the source you cite is not “outdated” – at that time we just didn’t have atmospheric constraints, only mass and radius. Also: the very fact that we see a water feature *implies* a H/He dominated atmosphere. There is no way around it.

There is a good Twitter thread about all this here, from Jessie Christiansen, a research scientist at NASA Exoplanet Science Institute (NExScI):

GUYS. Two independent announcements today of the same thing: We have found water vapor in the atmosphere of a planet called K2-18 b!

BUT WAIT?

WHAT DOES IT MEAN?

— Dr. Jessie Christiansen (@aussiastronomer) September 11, 2019

 

Also from Nature correspondent Alexandra Witze:

Some news today about K2-18b, a small planet 110 light-years from Earth. Hubble has spotted water vapor & possibly clouds in its atmosphere. https://t.co/3alGmHq9wS

— Alexandra Witze (@alexwitze) September 11, 2019

 

The planet is more of a mini-Neptune than a super-Earth: it's got a thick hydrogen atmosphere and if you want to find the water you'd have to go ballooning. But, the work is pushing the limits of understanding these alien worlds and how like (or unlike) Earth they may be.

— Alexandra Witze (@alexwitze) September 11, 2019

And another thread, from Marina Koren at The Atlantic:

1/ A thread about the big exoplanet news that was announced today, which—to be perfectly honest—was challenging for me to parse and report.. https://t.co/J1rstNGrpR

— Marina Koren (@marinakoren) September 11, 2019

So what about habitability? Since the planet is considered – by most scientists – to now be a mini-Neptune, this lowers the chances significantly. Water vapor itself, or even rain (as still considered possible in this planet’s atmosphere), is great, but life-as-we-know-it requires a rocky surface/interior for chemical nutrients, and bodies of liquid water. There may indeed be planets out there with life forms in only a gaseous atmosphere, but for Earth-kind of life at least, K2-18b would seem to be ill-suited for this.

There has been a lot of debate over whether K2-18b is a super-Earth or mini-Neptune. Most scientists now agree that it is a mini-Neptune, making habitability much less likely. Image via Patterson Clark/Washington Post/Quora.

Finding evidence for water vapor on a distant exoplanet in its star’s habitable zone is exciting, but in itself not proof of habitability. There are many factors that need to be considered, including composition of the planet and its atmosphere. However, K2-18b is the smallest exoplanet so far found to have water vapor in its atmosphere, which is a good sign: it supports the contention of scientists that even smaller planets with water vapor and/or liquid water will be found, worlds that are more Earth-like in terms of both size and composition. Upcoming space-based telescopes such as the James Webb Space Telescope (JWST) will be able to study the atmospheres of planets like this, and smaller, in greater detail than ever before, and even search for biosignatures, which could be evidence for life.

Bottom line: The exoplanet K2-18b does have water vapor in its atmosphere, but the planet itself is probably very un-Earth-like.

Source: Water vapour in the atmosphere of the habitable-zone eight-Earth-mass planet K2-18 b

Source: Water Vapor on the Habitable-Zone Exoplanet K2-18b

Via UCL News

from EarthSky https://ift.tt/34Lknrn

Artist’s concept of K2-18b, as well as another planet in this system, K2-18c, with the parent star, a red dwarf, in the background. Image via Alex Boersma/iREx.

A couple of days ago, EarthSky reported that for the first time ever, water vapor had been detected in the atmosphere of a potentially habitable super-Earth exoplanet. We weren’t alone in our report. As might be expected, the finding received a lot of attention from media. But, it turns out, that the story might not be quite as first reported and was mis-characterized to some extent.

The discovery was outlined in two different papers, the first one published on ArXiv on September 10, 2019 and the second in Nature Astronomy on September 11, 2019.

The papers detail the finding of water vapor in the atmosphere of K2-18b, an exoplanet in the habitable zone of its star – where temperatures could allow liquid water to exist – 110 light-years from Earth. It’s accurate that this is the first time that water vapor has been identified in the atmosphere of a smaller exoplanet (non-gas-giant) in the habitable zone of its star, but soon after the announcement, many planetary scientists critiqued how the discovery was covered in media and social media.

The water vapor detection itself is confirmed, but there is a lot of debate as to just what kind of planet K2-18b actually is, and how habitable it may be (or not).

Another artist’s concept of super-Earth K2-18b. Scientists have detected water vapor in its atmosphere, but is it habitable? Most scientists say it’s unlikely. Image via ESA/Hubble, M. Kornmesser/UCL News.

Some scientists, including in the Nature Astronomy paper, have referred to the planet as a super-Earth. A super-Earth is larger than Earth but smaller than Neptune – typically up to about a maximum of twice the size of Earth – and many have been discovered already. Most are thought to be rocky, like Earth, but there is a transition point – starting about 1.6 – two times Earth’s radius – where a planet can become a mini-gas-giant, or a mini-Neptune as they are usually called. They are larger than super-Earths, but still smaller than Neptune. Most scientists now consider K2-18b to be a mini-Neptune, not a super-Earth, with a deep atmosphere of hydrogen and/or helium, and possibly no solid surface at all.

K2-18b has a radius of about 2.7 times that of Earth, and a mass about nine times that of Earth. While some scientists would still consider that to be a possible super-Earth, most it seems would classify it as a mini-Neptune. All of this can be a bit confusing.

The 2017 study previously linked to considered that K2-18b might be either large and rocky or covered with water and/or ice. But that study didn’t account for atmospheric constraints, only mass and radius. As exoplanet scientist Erin May told me on Twitter:

My PhD partially focused on the distinction between these classes of planets. Many studies show that it’s extremely difficult to make a planet > than 2 Earth-radii without a large atmosphere. Mass & radius (density) alone are actually not very useful here. I’d also like to point out that from mass and radius alone, this planet should have never been considered a super-Earth. I think there’s a tendency to throw this term around because it’s more “exciting”, but we as astronomers need to keep our terminology straight.

Néstor Espinoza, an astronomer at the Max Planck Institute for Astronomy (MPIA), also told me:

If you believe the water feature, you have to believe it is an H/He dominated atmosphere so yes. And the source you cite is not “outdated” – at that time we just didn’t have atmospheric constraints, only mass and radius. Also: the very fact that we see a water feature *implies* a H/He dominated atmosphere. There is no way around it.

There is a good Twitter thread about all this here, from Jessie Christiansen, a research scientist at NASA Exoplanet Science Institute (NExScI):

GUYS. Two independent announcements today of the same thing: We have found water vapor in the atmosphere of a planet called K2-18 b!

BUT WAIT?

WHAT DOES IT MEAN?

— Dr. Jessie Christiansen (@aussiastronomer) September 11, 2019

 

Also from Nature correspondent Alexandra Witze:

Some news today about K2-18b, a small planet 110 light-years from Earth. Hubble has spotted water vapor & possibly clouds in its atmosphere. https://t.co/3alGmHq9wS

— Alexandra Witze (@alexwitze) September 11, 2019

 

The planet is more of a mini-Neptune than a super-Earth: it's got a thick hydrogen atmosphere and if you want to find the water you'd have to go ballooning. But, the work is pushing the limits of understanding these alien worlds and how like (or unlike) Earth they may be.

— Alexandra Witze (@alexwitze) September 11, 2019

And another thread, from Marina Koren at The Atlantic:

1/ A thread about the big exoplanet news that was announced today, which—to be perfectly honest—was challenging for me to parse and report.. https://t.co/J1rstNGrpR

— Marina Koren (@marinakoren) September 11, 2019

So what about habitability? Since the planet is considered – by most scientists – to now be a mini-Neptune, this lowers the chances significantly. Water vapor itself, or even rain (as still considered possible in this planet’s atmosphere), is great, but life-as-we-know-it requires a rocky surface/interior for chemical nutrients, and bodies of liquid water. There may indeed be planets out there with life forms in only a gaseous atmosphere, but for Earth-kind of life at least, K2-18b would seem to be ill-suited for this.

There has been a lot of debate over whether K2-18b is a super-Earth or mini-Neptune. Most scientists now agree that it is a mini-Neptune, making habitability much less likely. Image via Patterson Clark/Washington Post/Quora.

Finding evidence for water vapor on a distant exoplanet in its star’s habitable zone is exciting, but in itself not proof of habitability. There are many factors that need to be considered, including composition of the planet and its atmosphere. However, K2-18b is the smallest exoplanet so far found to have water vapor in its atmosphere, which is a good sign: it supports the contention of scientists that even smaller planets with water vapor and/or liquid water will be found, worlds that are more Earth-like in terms of both size and composition. Upcoming space-based telescopes such as the James Webb Space Telescope (JWST) will be able to study the atmospheres of planets like this, and smaller, in greater detail than ever before, and even search for biosignatures, which could be evidence for life.

Bottom line: The exoplanet K2-18b does have water vapor in its atmosphere, but the planet itself is probably very un-Earth-like.

Source: Water vapour in the atmosphere of the habitable-zone eight-Earth-mass planet K2-18 b

Source: Water Vapor on the Habitable-Zone Exoplanet K2-18b

Via UCL News

from EarthSky https://ift.tt/34Lknrn