The China National Space Administration’s (CNSA) Chang’e 6 lunar lander sits on the southern portion of the Apollo crater on the moon. The craft touched down there at 6:23 a.m. Beijing time, June 2 (June 1, 2024 at 22:23 UTC). On Tuesday, June 25, 2024, the mission’s sample return capsule landed in the Siziwang Banner province of China’s Inner Mongolia Autonomous Region. Credit: CNSA via NASA.
Far side lunar real estate came to Earth on Tuesday
In another success for the burgeoning Chinese space industry, the Chang’e 6 lunar probe touched down successfully on Tuesday, June 25, 2024 in the Inner Mongolia Autonomous Region, a province in the north of the country. The craft was launched by the China National Space Agency (CNSA) on May 3. It reached the moon June 1, and completed the lunar sample return mission 53 days later.
The probe made landfall in the Apollo Basin, a region in the South Pole-Aitken Basin, an enormous crater on the moon’s far side. This site is one of the oldest and largest impact features found in the solar system. It is 4 billion years old.
The sample is expected to contain 2.5 million-year-old lunar dust, aka regolith. AP reports China intends to share the sample with international researchers.
Chang’e 6 mission marks advance in lunar exploration
The sample of the little-studied far side of the moon will be of great interest to lunar geologists, as an ongoing international effort to return to Earth’s natural satellite continues gaining momentum. China is one of many countries – including the United States, Japan, South Korea, India and Russia – currently focused on establishing a long-term human presence on the lunar surface.
Primarily, the sample will provide insight into how the moon’s two faces differ. And it may offer clues to early solar system history hidden in ancient meteorite debris. But the real achievement of Chang’e 6 is technological, Richard de Grijs, a professor of astrophysics at Macquarie University in Australia, told the AP.
This is a global first in the sense that it’s the first time anyone has been able to take off from the far side of the moon and bring back samples.
Chang’e 6 demonstrates Chinese space program’s growing abilities
AP also quoted Chinese president Xi Jinping, who called the Chang’e 6 mission a “landmark achievement in our country’s efforts at becoming a space and technological power.”
And this wasn’t an easy assignment. NASA described Chang’e 6’s mission objectives:
The mission objective was to collect about 2 kg (4.4 pounds) of material from the far side of the moon and bring it back to Earth. A scoop and drill were used in order to obtain samples from the surface and from as deep as 2 meters (6.5 feet) below the surface. The samples were placed in the ascent vehicle, which was mounted on top of the lander.
The lander also deployed a small rover, which snapped a picture of its mothership (see above). Once aloft, the ascent vehicle mated with the Chang’e 6 orbiter, transferred the lunar sample and crashed back into the lunar surface. The return vehicle left the moon’s orbit around June 21.
Bottom line: The Chinese moon mission Chang’e 6 brought the first sample of the moon’s far side ever returned to Earth on Tuesday, June 25, 2024. The craft reached the moon 25 days earlier.
The China National Space Administration’s (CNSA) Chang’e 6 lunar lander sits on the southern portion of the Apollo crater on the moon. The craft touched down there at 6:23 a.m. Beijing time, June 2 (June 1, 2024 at 22:23 UTC). On Tuesday, June 25, 2024, the mission’s sample return capsule landed in the Siziwang Banner province of China’s Inner Mongolia Autonomous Region. Credit: CNSA via NASA.
Far side lunar real estate came to Earth on Tuesday
In another success for the burgeoning Chinese space industry, the Chang’e 6 lunar probe touched down successfully on Tuesday, June 25, 2024 in the Inner Mongolia Autonomous Region, a province in the north of the country. The craft was launched by the China National Space Agency (CNSA) on May 3. It reached the moon June 1, and completed the lunar sample return mission 53 days later.
The probe made landfall in the Apollo Basin, a region in the South Pole-Aitken Basin, an enormous crater on the moon’s far side. This site is one of the oldest and largest impact features found in the solar system. It is 4 billion years old.
The sample is expected to contain 2.5 million-year-old lunar dust, aka regolith. AP reports China intends to share the sample with international researchers.
Chang’e 6 mission marks advance in lunar exploration
The sample of the little-studied far side of the moon will be of great interest to lunar geologists, as an ongoing international effort to return to Earth’s natural satellite continues gaining momentum. China is one of many countries – including the United States, Japan, South Korea, India and Russia – currently focused on establishing a long-term human presence on the lunar surface.
Primarily, the sample will provide insight into how the moon’s two faces differ. And it may offer clues to early solar system history hidden in ancient meteorite debris. But the real achievement of Chang’e 6 is technological, Richard de Grijs, a professor of astrophysics at Macquarie University in Australia, told the AP.
This is a global first in the sense that it’s the first time anyone has been able to take off from the far side of the moon and bring back samples.
Chang’e 6 demonstrates Chinese space program’s growing abilities
AP also quoted Chinese president Xi Jinping, who called the Chang’e 6 mission a “landmark achievement in our country’s efforts at becoming a space and technological power.”
And this wasn’t an easy assignment. NASA described Chang’e 6’s mission objectives:
The mission objective was to collect about 2 kg (4.4 pounds) of material from the far side of the moon and bring it back to Earth. A scoop and drill were used in order to obtain samples from the surface and from as deep as 2 meters (6.5 feet) below the surface. The samples were placed in the ascent vehicle, which was mounted on top of the lander.
The lander also deployed a small rover, which snapped a picture of its mothership (see above). Once aloft, the ascent vehicle mated with the Chang’e 6 orbiter, transferred the lunar sample and crashed back into the lunar surface. The return vehicle left the moon’s orbit around June 21.
Bottom line: The Chinese moon mission Chang’e 6 brought the first sample of the moon’s far side ever returned to Earth on Tuesday, June 25, 2024. The craft reached the moon 25 days earlier.
Libra the Scales is a zodiac constellation home to 2 stars with pleasing names: Zubeneschamali and Zubenelgenubi. Chart via EarthSky.
Look for the constellation Libra the Scales on Northern Hemisphere summer evenings (Southern Hemisphere winter evenings). It’s not the most flashy constellation of the zodiac. But its two brightest stars have the best star names: Zubenelgenubi and Zubeneschamali. The names rhyme with Obi-Wan Kenobi of “Star Wars.”
You can find Libra easily in a dark sky. On the chart below, notice Libra’s place with respect to another even brighter star, red Antares, Heart of the Scorpion in the constellation Scorpius. The Scorpion has a distinctive shape. And Antares is noticeable for being bright, and red, and for twinkling fiercely. Find Antares … and Libra will be nearby.
In Libra, Zubenelgenubi is a bit fainter than Libra’s other bright star Zubeneschamali. But it lies nearly on the ecliptic, or pathway of the sun, moon and planets. That might be why the ancient stargazers gave Zubenelgenubi the alpha designation within this constellation. Image via International Astronomical Union/ Sky and Telescope/ Wikimedia Commons (CC BY 3.0).
Libra and the ecliptic
Libra is a constellation of the zodiac. So you know to look for it along the sun’s path across our sky. This path is the ecliptic. As seen from Earth, the sun passes in front of the constellation Libra from about October 30 until November 22 every year.
Libra’s star Zubenelgenubi sits almost exactly on the ecliptic. At present, the sun has its annual conjunction with Zubenelgenubi on or near November 7, or about midway between the September equinox and the December solstice.
But, as with all things heavenly, the conjunction date of the sun and Zubenelgenubi changes over the long course of time.
More than 3,000 years ago, the sun and Zubenelgenubi were in conjunction on the Northern Hemisphere’s autumnal equinox (Southern Hemisphere’s spring equinox). Over 3,000 years into the future, the sun and Zubenelgenubi will be in conjunction on the December solstice (Northern Hemisphere’s winter solstice or Southern Hemisphere’s summer solstice).
Regardless of which constellation provides a backdrop for the sun on the September equinox, the sun is said to be at the first point of the sign Libra when it the crosses the celestial equator going from north to south.
The constellation Libra from Urania’s Mirror, a boxed set of 32 constellation cards printed about 1825. Image via Wikipedia (public domain).
Libra in history and myth
Several thousand years ago – around 2,000 BCE – the ancient Babylonians apparently associated this constellation with scales or a balance. Quite possibly, they made this association because the sun on the autumnal equinox shone in front of the stars of Libra at that time. It’s at the equinox that the world realizes its seasonal and temporal balance between the extremes of heat and cold, and with day and night of equal length all over the globe. Metaphorically, Libra the Scales serves as an age-old symbol of divine justice, harmony and balance.
In contrast to their Babylonian forebears, the ancient Greeks seemed to regard Libra as the outstretched claws of the constellation Scorpius the Scorpion. In fact, the names for Libra’s two brightest stars are Arabic terms that hearken back to these olden times when Scorpius reigned as a double or super constellation. Zubenelgenubi translates into the southern claw of the Scorpion and Zubeneschamali into the northern claw of the Scorpion.
The Romans, though inheriting much of the Greek tradition, again revived Libra as the only inanimate constellation of the zodiac. In Roman thought, the constellation Virgo is the embodiment of Astraea, the Starry Goddess, holding Libra, the Scales of Justice.
Astrologers regard Libra as the second air sign, ruled over by the planet Venus. Although astronomy and astrology have been intertwined historically, they are now regarded as separate disciplines. Astrology assumes the positions of heavenly bodies have certain influences over human affairs which most modern-day astronomers regard as unfounded.
According to mythology, at the return of the golden age the goddess Astraea will dispense justice and weigh the souls of men. Image via Wikipedia (GFDL 1.2).
Bottom line: Find the zodiacal constellation Libra the Scales in the evening sky during Northern Hemisphere summer (Southern Hemisphere winter) near the bright red star Antares.
Libra the Scales is a zodiac constellation home to 2 stars with pleasing names: Zubeneschamali and Zubenelgenubi. Chart via EarthSky.
Look for the constellation Libra the Scales on Northern Hemisphere summer evenings (Southern Hemisphere winter evenings). It’s not the most flashy constellation of the zodiac. But its two brightest stars have the best star names: Zubenelgenubi and Zubeneschamali. The names rhyme with Obi-Wan Kenobi of “Star Wars.”
You can find Libra easily in a dark sky. On the chart below, notice Libra’s place with respect to another even brighter star, red Antares, Heart of the Scorpion in the constellation Scorpius. The Scorpion has a distinctive shape. And Antares is noticeable for being bright, and red, and for twinkling fiercely. Find Antares … and Libra will be nearby.
In Libra, Zubenelgenubi is a bit fainter than Libra’s other bright star Zubeneschamali. But it lies nearly on the ecliptic, or pathway of the sun, moon and planets. That might be why the ancient stargazers gave Zubenelgenubi the alpha designation within this constellation. Image via International Astronomical Union/ Sky and Telescope/ Wikimedia Commons (CC BY 3.0).
Libra and the ecliptic
Libra is a constellation of the zodiac. So you know to look for it along the sun’s path across our sky. This path is the ecliptic. As seen from Earth, the sun passes in front of the constellation Libra from about October 30 until November 22 every year.
Libra’s star Zubenelgenubi sits almost exactly on the ecliptic. At present, the sun has its annual conjunction with Zubenelgenubi on or near November 7, or about midway between the September equinox and the December solstice.
But, as with all things heavenly, the conjunction date of the sun and Zubenelgenubi changes over the long course of time.
More than 3,000 years ago, the sun and Zubenelgenubi were in conjunction on the Northern Hemisphere’s autumnal equinox (Southern Hemisphere’s spring equinox). Over 3,000 years into the future, the sun and Zubenelgenubi will be in conjunction on the December solstice (Northern Hemisphere’s winter solstice or Southern Hemisphere’s summer solstice).
Regardless of which constellation provides a backdrop for the sun on the September equinox, the sun is said to be at the first point of the sign Libra when it the crosses the celestial equator going from north to south.
The constellation Libra from Urania’s Mirror, a boxed set of 32 constellation cards printed about 1825. Image via Wikipedia (public domain).
Libra in history and myth
Several thousand years ago – around 2,000 BCE – the ancient Babylonians apparently associated this constellation with scales or a balance. Quite possibly, they made this association because the sun on the autumnal equinox shone in front of the stars of Libra at that time. It’s at the equinox that the world realizes its seasonal and temporal balance between the extremes of heat and cold, and with day and night of equal length all over the globe. Metaphorically, Libra the Scales serves as an age-old symbol of divine justice, harmony and balance.
In contrast to their Babylonian forebears, the ancient Greeks seemed to regard Libra as the outstretched claws of the constellation Scorpius the Scorpion. In fact, the names for Libra’s two brightest stars are Arabic terms that hearken back to these olden times when Scorpius reigned as a double or super constellation. Zubenelgenubi translates into the southern claw of the Scorpion and Zubeneschamali into the northern claw of the Scorpion.
The Romans, though inheriting much of the Greek tradition, again revived Libra as the only inanimate constellation of the zodiac. In Roman thought, the constellation Virgo is the embodiment of Astraea, the Starry Goddess, holding Libra, the Scales of Justice.
Astrologers regard Libra as the second air sign, ruled over by the planet Venus. Although astronomy and astrology have been intertwined historically, they are now regarded as separate disciplines. Astrology assumes the positions of heavenly bodies have certain influences over human affairs which most modern-day astronomers regard as unfounded.
According to mythology, at the return of the golden age the goddess Astraea will dispense justice and weigh the souls of men. Image via Wikipedia (GFDL 1.2).
Bottom line: Find the zodiacal constellation Libra the Scales in the evening sky during Northern Hemisphere summer (Southern Hemisphere winter) near the bright red star Antares.
View larger. | Artist’s concept of Kraken Mare, the largest methane/ethane sea on Titan. A new study from MIT and the U.S. Geological Survey suggests the shorelines of Titan’s seas are likely being shaped by waves. Image via NASA/ John Glenn Research Center/ Cornell University.
Liquid methane and ethane, not water, make up the liquid in Titan’s seas and smaller lakes. Temperatures on this large moon of Saturn – in the outer solar system – are too cold for liquid water. NASA’s Cassini spacecraft first saw Titan’s seas and lakes in 2007.
The shorelines of Titan’s seas are most likely created by waves, just as on Earth, according to new research.
The researchers tested three different possible computer models. The wave scenario fit the data best for all of Titan’s largest seas.
Would shorelines of Titan’s seas remind us of home?
Much like Earth, Saturn’s large moon Titan has rivers, lakes and seas. Although they are composed of liquid methane and ethane instead of water, these bodies of liquid look – in spacecraft images – like their earthly counterparts, especially when sunlight is glinting off their surfaces. And scientists have wondered, how similar might they be? For example, do Titan’s seas, or even smaller lakes, have waves? If so, do the waves erode Titan’s coastlines as waves do on our planet? On June 19, 2024, scientists at the Massachusetts Institute of Technology (MIT) and the U.S. Geological Survey said new simulations suggest waves do help shape Titan’s seas and lakes.
The researchers published their peer-reviewed findings in Science Advances on June 19, 2024.
Titan’s seas and lakes
Scientists had long speculated there might be seas on Titan, based on what they knew about its climate and other factors. And NASA’s Cassini mission confirmed their existence in 2007. They are mostly scattered around the moon’s north pole, along with smaller lakes and rivers. In radar images from Cassini – to see through Titan’s thick, smoggy atmosphere – they looked just like seas and lakes on Earth.
But in Titan’s extreme cold, they’re composed of liquid hydrocarbons, methane and ethane, instead of water. Interestingly though, there is evidence for previous ancient water lakes on Titan that may have lasted for tens of thousands of years.
Waves on Titan’s seas?
Scientists wanted to know if those seas and lakes had waves, too. So far, analysis results had been a bit contradictory and uncertain. Some research had suggested the seas and lakes were fairly flat, with little to no wave activity.
Rose Palermo, formerly at MIT and now a research geologist at the the U.S. Geological Survey, said:
Some people who tried to see evidence for waves didn’t see any, and said, ‘These seas are mirror-smooth.’ Others said they did see some roughness on the liquid surface but weren’t sure if waves caused it.
View larger. | NASA’s Cassini spacecraft captured this radar image of Ligeia Mare, another large sea on Titan, in 2007. Image via Image via NASA/ JPL-Caltech/ ASI/ Cornell.
Waves likely caused erosion on shorelines of Titan’s seas
But the researchers at MIT took a different approach. They focused more on the shorelines, to see if waves could explain erosion along the edges of the seas and lakes. Did waves produce the erosion, or something else? As it turned out, waves were the most likely explanation. Taylor Perron, at Earth, Atmospheric and Planetary Sciences at MIT, said:
We can say, based on our results, that if the coastlines of Titan’s seas have eroded, waves are the most likely culprit. If we could stand at the edge of one of Titan’s seas, we might see waves of liquid methane and ethane lapping on the shore and crashing on the coasts during storms. And they would be capable of eroding the material that the coast is made of.
Perron noted the team had to:
… take a different tack, and see, just by looking at the shape of the shoreline, if we could tell what’s been eroding the coasts.
All four of Titan’s largest lakes – also referred to as seas – fit the wave model the best. This includes Kraken Mare, similar in size to the Caspian Sea; Ligeia Mare, larger than Lake Superior; Punga Mare, longer than Lake Victoria and Ontario Lacus, which is about 20% the size of Lake Ontario on Earth. Perron said:
We found that if the coastlines have eroded, their shapes are more consistent with erosion by waves than by uniform erosion or no erosion at all.
Possible erosion scenarios on shorelines of Titan’s seas
The researchers had proposed three possible scenarios. In the first, there is no coastal erosion. The second suggests erosion driven by waves. In the third, “uniform erosion” is driven either by “dissolution, ” where a liquid passively dissolves a coast’s material, or a mechanism in which the coast gradually sloughs off under its own weight.
To determine which scenario was correct, the researchers simulated how the shorelines would evolve for each one. For erosion involving waves, they used a variable called fetch. That is the physical distance from one point on the shoreline to a point on the opposite side of the lake or sea. The researchers could use this to estimate the height of possible waves. Palermo explained:
Wave erosion is driven by the height and angle of the wave. We used fetch to approximate wave height because the bigger the fetch, the longer the distance over which wind can blow and waves can grow.
Different scenarios produce different shorelines
So what kinds of shorelines would the three scenarios produce? To test this, the researchers simulated a sea with flooded river valleys around it. They started with the wave-driven erosion scenario. To try to determine wave height, they calculated the fetch distance from points along the shoreline to every other point. Then, they could estimate how those waves would erode the shoreline over time.
Next, the team compared those results to those of uniform erosion. They then repeated the simulations using hundreds of different original shapes of shorelines (before erosion). As might be expected, different scenarios produced various results.
Wave erosion and uniform erosion had markedly different outcomes. Wave erosion tended to smooth out the parts of shorelines with the longest fetch distances. That caused the flooded valleys to be narrow and rough. On the other hand, uniform erosion created shorelines that widened all the way around the lake or sea. This even occurred in the flooded valleys.
So even though the original shoreline was the same in each scenario, the different types of erosion produced very different results, as Perron said:
We had the same starting shorelines, and we saw that you get a really different final shape under uniform erosion versus wave erosion. They all kind of look like the flying spaghetti monster because of the flooded river valleys, but the two types of erosion produce very different endpoints.
The results were also found to be similar to lakes on Earth with the two different forms of erosion.
Artist’s concept of some smaller lakes on Titan. Image via NASA/ JPL/ University of Arizona/ University of Idaho/ Massachusetts Institute of Technology.
Watching the waves on Titan’s seas
So, what would it be like to be able to stand on the shoreline of a Titanian sea and watch the waves? Overall, it would be similar to seeing waves crash on or lap at a shoreline on Earth. As Juan Felipe Paniagua-Arroyave at the School of Applied Sciences and Engineering at EAFIT University in Colombia noted:
Waves are ubiquitous on Earth’s oceans. If Titan has waves, they would likely dominate the surface of lakes. It would be fascinating to see how Titan’s winds create waves, not of water, but of exotic liquid hydrocarbons.
Palermo added:
Titan presents this case of a completely untouched system. It could help us learn more fundamental things about how coasts erode without the influence of people, and maybe that can help us better manage our coastlines on Earth in the future.
Bottom line: Saturn’s largest moon Titan has seas and lakes of liquid methane and ethane. A new study from MIT suggests the shorelines of Titan’s seas are shaped by waves.
View larger. | Artist’s concept of Kraken Mare, the largest methane/ethane sea on Titan. A new study from MIT and the U.S. Geological Survey suggests the shorelines of Titan’s seas are likely being shaped by waves. Image via NASA/ John Glenn Research Center/ Cornell University.
Liquid methane and ethane, not water, make up the liquid in Titan’s seas and smaller lakes. Temperatures on this large moon of Saturn – in the outer solar system – are too cold for liquid water. NASA’s Cassini spacecraft first saw Titan’s seas and lakes in 2007.
The shorelines of Titan’s seas are most likely created by waves, just as on Earth, according to new research.
The researchers tested three different possible computer models. The wave scenario fit the data best for all of Titan’s largest seas.
Would shorelines of Titan’s seas remind us of home?
Much like Earth, Saturn’s large moon Titan has rivers, lakes and seas. Although they are composed of liquid methane and ethane instead of water, these bodies of liquid look – in spacecraft images – like their earthly counterparts, especially when sunlight is glinting off their surfaces. And scientists have wondered, how similar might they be? For example, do Titan’s seas, or even smaller lakes, have waves? If so, do the waves erode Titan’s coastlines as waves do on our planet? On June 19, 2024, scientists at the Massachusetts Institute of Technology (MIT) and the U.S. Geological Survey said new simulations suggest waves do help shape Titan’s seas and lakes.
The researchers published their peer-reviewed findings in Science Advances on June 19, 2024.
Titan’s seas and lakes
Scientists had long speculated there might be seas on Titan, based on what they knew about its climate and other factors. And NASA’s Cassini mission confirmed their existence in 2007. They are mostly scattered around the moon’s north pole, along with smaller lakes and rivers. In radar images from Cassini – to see through Titan’s thick, smoggy atmosphere – they looked just like seas and lakes on Earth.
But in Titan’s extreme cold, they’re composed of liquid hydrocarbons, methane and ethane, instead of water. Interestingly though, there is evidence for previous ancient water lakes on Titan that may have lasted for tens of thousands of years.
Waves on Titan’s seas?
Scientists wanted to know if those seas and lakes had waves, too. So far, analysis results had been a bit contradictory and uncertain. Some research had suggested the seas and lakes were fairly flat, with little to no wave activity.
Rose Palermo, formerly at MIT and now a research geologist at the the U.S. Geological Survey, said:
Some people who tried to see evidence for waves didn’t see any, and said, ‘These seas are mirror-smooth.’ Others said they did see some roughness on the liquid surface but weren’t sure if waves caused it.
View larger. | NASA’s Cassini spacecraft captured this radar image of Ligeia Mare, another large sea on Titan, in 2007. Image via Image via NASA/ JPL-Caltech/ ASI/ Cornell.
Waves likely caused erosion on shorelines of Titan’s seas
But the researchers at MIT took a different approach. They focused more on the shorelines, to see if waves could explain erosion along the edges of the seas and lakes. Did waves produce the erosion, or something else? As it turned out, waves were the most likely explanation. Taylor Perron, at Earth, Atmospheric and Planetary Sciences at MIT, said:
We can say, based on our results, that if the coastlines of Titan’s seas have eroded, waves are the most likely culprit. If we could stand at the edge of one of Titan’s seas, we might see waves of liquid methane and ethane lapping on the shore and crashing on the coasts during storms. And they would be capable of eroding the material that the coast is made of.
Perron noted the team had to:
… take a different tack, and see, just by looking at the shape of the shoreline, if we could tell what’s been eroding the coasts.
All four of Titan’s largest lakes – also referred to as seas – fit the wave model the best. This includes Kraken Mare, similar in size to the Caspian Sea; Ligeia Mare, larger than Lake Superior; Punga Mare, longer than Lake Victoria and Ontario Lacus, which is about 20% the size of Lake Ontario on Earth. Perron said:
We found that if the coastlines have eroded, their shapes are more consistent with erosion by waves than by uniform erosion or no erosion at all.
Possible erosion scenarios on shorelines of Titan’s seas
The researchers had proposed three possible scenarios. In the first, there is no coastal erosion. The second suggests erosion driven by waves. In the third, “uniform erosion” is driven either by “dissolution, ” where a liquid passively dissolves a coast’s material, or a mechanism in which the coast gradually sloughs off under its own weight.
To determine which scenario was correct, the researchers simulated how the shorelines would evolve for each one. For erosion involving waves, they used a variable called fetch. That is the physical distance from one point on the shoreline to a point on the opposite side of the lake or sea. The researchers could use this to estimate the height of possible waves. Palermo explained:
Wave erosion is driven by the height and angle of the wave. We used fetch to approximate wave height because the bigger the fetch, the longer the distance over which wind can blow and waves can grow.
Different scenarios produce different shorelines
So what kinds of shorelines would the three scenarios produce? To test this, the researchers simulated a sea with flooded river valleys around it. They started with the wave-driven erosion scenario. To try to determine wave height, they calculated the fetch distance from points along the shoreline to every other point. Then, they could estimate how those waves would erode the shoreline over time.
Next, the team compared those results to those of uniform erosion. They then repeated the simulations using hundreds of different original shapes of shorelines (before erosion). As might be expected, different scenarios produced various results.
Wave erosion and uniform erosion had markedly different outcomes. Wave erosion tended to smooth out the parts of shorelines with the longest fetch distances. That caused the flooded valleys to be narrow and rough. On the other hand, uniform erosion created shorelines that widened all the way around the lake or sea. This even occurred in the flooded valleys.
So even though the original shoreline was the same in each scenario, the different types of erosion produced very different results, as Perron said:
We had the same starting shorelines, and we saw that you get a really different final shape under uniform erosion versus wave erosion. They all kind of look like the flying spaghetti monster because of the flooded river valleys, but the two types of erosion produce very different endpoints.
The results were also found to be similar to lakes on Earth with the two different forms of erosion.
Artist’s concept of some smaller lakes on Titan. Image via NASA/ JPL/ University of Arizona/ University of Idaho/ Massachusetts Institute of Technology.
Watching the waves on Titan’s seas
So, what would it be like to be able to stand on the shoreline of a Titanian sea and watch the waves? Overall, it would be similar to seeing waves crash on or lap at a shoreline on Earth. As Juan Felipe Paniagua-Arroyave at the School of Applied Sciences and Engineering at EAFIT University in Colombia noted:
Waves are ubiquitous on Earth’s oceans. If Titan has waves, they would likely dominate the surface of lakes. It would be fascinating to see how Titan’s winds create waves, not of water, but of exotic liquid hydrocarbons.
Palermo added:
Titan presents this case of a completely untouched system. It could help us learn more fundamental things about how coasts erode without the influence of people, and maybe that can help us better manage our coastlines on Earth in the future.
Bottom line: Saturn’s largest moon Titan has seas and lakes of liquid methane and ethane. A new study from MIT suggests the shorelines of Titan’s seas are shaped by waves.
Summer is lightning season. You’ve probably heard the saying, ‘When thunder roars, go indoors.’ Learn more lightning safety tips here. Image via Pixabay/ Pexels.
As the weather warms, people spend more time outdoors, going to barbecues, beaches and ballgames. But summer isn’t just the season of baseball and outdoor festivals. It’s also lightning season.
Each year in the United States, lightning strikes around 37 million times. It kills 21 people a year in the U.S. on average.
For as often as lightning occurs – there are only a few days each year nationwide without lightning – there are still a lot of misunderstandings about nature’s largest spark. Because of this, a lot of people take unnecessary risks when thunderstorms are nearby.
I am a meteorologist who studies lightning and lightning safety, and a member of the National Lightning Safety Council. Here are some fast facts to keep your family and friends safe this summer:
What is lightning, and where does it come from?
Lightning is a giant electric spark in the atmosphere. It’s classified based on whether it hits the ground or not.
In-cloud lightning is any lightning that doesn’t hit ground, while cloud-to-ground – or, less commonly, ground-to-cloud – is any lightning that hits an object on the ground. Cloud-to-ground lightning accounts for only 10% to 50% of the lightning in a thunderstorm, but it can cause damage, including fires, injuries and fatalities. So it’s important to know where it is striking.
When these precipitation particles collide, they exchange electrons, which creates an electric charge in the cloud. Because most of the electric charge exists in the clouds, most lightning happens in the clouds. When the electric charge in the cloud is strong, it can cause an opposite charge to build up on the ground, making cloud-to-ground lightning possible. Exactly what initiates a strike is still an open question.
When and where does lightning happen?
Lightning can happen any time the conditions for thunderstorms – moisture, atmospheric instability, and a way for air to rise – are present.
There is a seasonality to lightning: Most lightning in the United States strikes in June, July or August. In just those three months, more than 60% of the year’s lightning typically occurs. Lightning is least common in winter, but it can still happen. About 2% of yearly lightning occurs during winter.
No state is immune from lightning, but it is more common in some states than others.
Texas, Florida, Oklahoma, Louisiana and Mississippi are often among the leaders in total lightning strikes, but more than 30 states regularly see at least 1 million in-cloud and cloud-to-ground lightning events each year.
Lightning safety
Almost three-quarters of U.S. lightning fatalities occur between June and August. Luckily, staying safe from lightning is easy.
Keep an eye on the forecast and reconsider outdoor plans if thunderstorms are expected, especially if those plans take you near the water. Beaches are dangerous because lightning tends to strike the highest object, and water is a good conductor of electricity, so you don’t want to be in it.
Remember: No place outside is safe during a thunderstorm. So when thunder roars, go indoors. When you see the clouds building up, hear thunder or see a flash of lightning, it’s time to dash inside to a lightning-safe place.
What is a lightning-safe place?
There are two safe places to be during a thunderstorm: a substantial building or a fully enclosed metal vehicle.
A substantial building is a house, store, office building or other structure that has four walls and a roof, and where the electrical wiring and plumbing are protected inside the walls. If lightning strikes the building or near it, the electricity from the lightning travels through the walls and not through you. Dugouts, picnic shelters and gazebos are not safe places.
If you’re in a fully enclosed metal vehicle during a thunderstorm and lightning strikes, the electricity travels through the metal shell, which keeps you safe. It’s not the rubber tires that protect you. That’s a common myth. So, golf carts and convertibles won’t keep you safe if lightning strikes.
When you’re outdoors and lightning approaches, head to a lightning-safe place, even if it’s a distance away. Stay away from trees, especially tall and isolated ones, and don’t crouch in place. It doesn’t make you safer and just keeps you in the storm for longer.
Stay safe this summer
While you’re enjoying your summer plans, keep lightning safety in mind.
Bottom line: Get your lightning safety tips here. Do you know whether it’s safe to be at the beach during a lightning storm? How about in a golf cart? And what percentage of people die after being struck by lightning?
Summer is lightning season. You’ve probably heard the saying, ‘When thunder roars, go indoors.’ Learn more lightning safety tips here. Image via Pixabay/ Pexels.
As the weather warms, people spend more time outdoors, going to barbecues, beaches and ballgames. But summer isn’t just the season of baseball and outdoor festivals. It’s also lightning season.
Each year in the United States, lightning strikes around 37 million times. It kills 21 people a year in the U.S. on average.
For as often as lightning occurs – there are only a few days each year nationwide without lightning – there are still a lot of misunderstandings about nature’s largest spark. Because of this, a lot of people take unnecessary risks when thunderstorms are nearby.
I am a meteorologist who studies lightning and lightning safety, and a member of the National Lightning Safety Council. Here are some fast facts to keep your family and friends safe this summer:
What is lightning, and where does it come from?
Lightning is a giant electric spark in the atmosphere. It’s classified based on whether it hits the ground or not.
In-cloud lightning is any lightning that doesn’t hit ground, while cloud-to-ground – or, less commonly, ground-to-cloud – is any lightning that hits an object on the ground. Cloud-to-ground lightning accounts for only 10% to 50% of the lightning in a thunderstorm, but it can cause damage, including fires, injuries and fatalities. So it’s important to know where it is striking.
When these precipitation particles collide, they exchange electrons, which creates an electric charge in the cloud. Because most of the electric charge exists in the clouds, most lightning happens in the clouds. When the electric charge in the cloud is strong, it can cause an opposite charge to build up on the ground, making cloud-to-ground lightning possible. Exactly what initiates a strike is still an open question.
When and where does lightning happen?
Lightning can happen any time the conditions for thunderstorms – moisture, atmospheric instability, and a way for air to rise – are present.
There is a seasonality to lightning: Most lightning in the United States strikes in June, July or August. In just those three months, more than 60% of the year’s lightning typically occurs. Lightning is least common in winter, but it can still happen. About 2% of yearly lightning occurs during winter.
No state is immune from lightning, but it is more common in some states than others.
Texas, Florida, Oklahoma, Louisiana and Mississippi are often among the leaders in total lightning strikes, but more than 30 states regularly see at least 1 million in-cloud and cloud-to-ground lightning events each year.
Lightning safety
Almost three-quarters of U.S. lightning fatalities occur between June and August. Luckily, staying safe from lightning is easy.
Keep an eye on the forecast and reconsider outdoor plans if thunderstorms are expected, especially if those plans take you near the water. Beaches are dangerous because lightning tends to strike the highest object, and water is a good conductor of electricity, so you don’t want to be in it.
Remember: No place outside is safe during a thunderstorm. So when thunder roars, go indoors. When you see the clouds building up, hear thunder or see a flash of lightning, it’s time to dash inside to a lightning-safe place.
What is a lightning-safe place?
There are two safe places to be during a thunderstorm: a substantial building or a fully enclosed metal vehicle.
A substantial building is a house, store, office building or other structure that has four walls and a roof, and where the electrical wiring and plumbing are protected inside the walls. If lightning strikes the building or near it, the electricity from the lightning travels through the walls and not through you. Dugouts, picnic shelters and gazebos are not safe places.
If you’re in a fully enclosed metal vehicle during a thunderstorm and lightning strikes, the electricity travels through the metal shell, which keeps you safe. It’s not the rubber tires that protect you. That’s a common myth. So, golf carts and convertibles won’t keep you safe if lightning strikes.
When you’re outdoors and lightning approaches, head to a lightning-safe place, even if it’s a distance away. Stay away from trees, especially tall and isolated ones, and don’t crouch in place. It doesn’t make you safer and just keeps you in the storm for longer.
Stay safe this summer
While you’re enjoying your summer plans, keep lightning safety in mind.
Bottom line: Get your lightning safety tips here. Do you know whether it’s safe to be at the beach during a lightning storm? How about in a golf cart? And what percentage of people die after being struck by lightning?
The Summer Triangle, ascending in the east on June evenings. Chart via Chelynne Campion.
Summertime is Summer Triangle time
During the summertime in the Northern Hemisphere, the days are long. The sun is high in the midday sky. And the summer sky is with us, too. Watch for the famous Summer Triangle, now ascending in the eastern sky on these late June and July evenings.
The Summer Triangle isn’t a constellation. It’s an asterism, or noticeable pattern of stars. This pattern consists of three bright stars in three separate constellations – Deneb in the constellation Cygnus the Swan, Vega in the constellation Lyra the Harp, and Altair in the constellation Aquila the Eagle.
Learn to recognize the Summer Triangle asterism now, and you can watch it all summer as it shifts higher in the east, then finally appears high overhead in the late northern summer and early northern autumn sky.
How to find the Summer Triangle
As night falls in June or July, look east for a sparkling blue-white star. That will be Vega, in Lyra. Reigning at the apex of the celebrated Summer Triangle, Vega is also the brightest of the Summer Triangle’s three stars, which are all bright enough to be seen from many light-polluted cities.
Look to the lower right of Vega to locate the Summer Triangle’s second brightest star. That’s Altair, the brightest star in the constellation Aquila the Eagle. A ruler (12 inches, 30 cm) held at arm’s length fills the gap between these two stars.
Look to the lower left of Vega for another bright star: Deneb, the brightest in the constellation Cygnus the Swan and the third brightest in the Summer Triangle. An outstretched hand at arm’s length approximates the distance from Vega to Deneb.
It’s difficult to convey the huge size of the Summer Triangle. But you’ll see it. These three bright stars – Vega, Deneb and Altair – will become summertime favorites.
Once Cygnus the Swan clears the horizon, you can easily see all of the Summer Triangle asterism. It’s a summertime favorite and easy to see.View at EarthSky Community Photos. | Dr Ski in Valencia, Philippines, captured the Summer Triangle and wrote: “The line between Vega and Altair is broken so as not to obscure the Coathanger Cluster.”
Summer Triangle as a road map to the Milky Way
If you’re lucky enough to be under a dark starry sky on a moonless night, you’ll see the great swath of stars passing between the Summer Triangle’s Vega and Altair. The star Deneb bobs in the middle of this river of stars, which arcs across dark summer skies. This sky river is, of course, the edgewise view into our own Milky Way galaxy. Every star you see with the unaided eye is a member of the Milky Way. And at this time of year, we can see clearly into the galaxy’s flat disk, where most of the stars congregate. By August and September, we will have a good view toward the galaxy’s center.
Once you master the Summer Triangle, you can always locate the Milky Way on a clear, dark night. How about making the most of a dark summer night to explore this band of stars, this starlit boulevard with its celestial delights? Use binoculars to reveal the gossamer beauty of the haunting nebulae and bejeweled star clusters along this starlit trail.
The 3 brightest stars in this image make up the asterism of the Summer Triangle, a giant triangle in the sky composed of the bright stars Vega (top left), Altair (lower middle) and Deneb (far left). Also in this image, under a dark sky and on a moonless night, is the Great Rift that passes right through the Milky Way and the Summer Triangle. Image via NASA/ A. Fujii/ ESA.
Nature’s seasonal calendar
Also, the Summer Triangle serves as a stellar calendar, marking the seasons. So when the stars of the Summer Triangle light up the eastern twilight dusk in middle to late June, it’s a sure sign of the change of seasons, of spring giving way to summer. However, when the Summer Triangle is high in the south to overhead at dusk and early evening, the Summer Triangle’s change of position indicates that summer has ebbed into fall.
A word about asterisms
As we mentioned above, asterisms aren’t constellations; they’re just patterns on the sky’s dome. Constellations generally come to us from ancient times. In the 1930s, the International Astronomical Union officially drew the boundaries of the 88 constellations we recognize today.
Meanwhile, you can make up and name your own asterisms, in much the same way you can recognize shapes in puffy clouds on a summer day.
Of course, some asterisms are so obvious that they’re recognized around the world. And the Summer Triangle is one of these.
Bottom line: On June and July evenings, you’ll find the Summer Triangle in the east at nightfall. It swings high overhead after midnight and sits in the west at daybreak.
The Summer Triangle, ascending in the east on June evenings. Chart via Chelynne Campion.
Summertime is Summer Triangle time
During the summertime in the Northern Hemisphere, the days are long. The sun is high in the midday sky. And the summer sky is with us, too. Watch for the famous Summer Triangle, now ascending in the eastern sky on these late June and July evenings.
The Summer Triangle isn’t a constellation. It’s an asterism, or noticeable pattern of stars. This pattern consists of three bright stars in three separate constellations – Deneb in the constellation Cygnus the Swan, Vega in the constellation Lyra the Harp, and Altair in the constellation Aquila the Eagle.
Learn to recognize the Summer Triangle asterism now, and you can watch it all summer as it shifts higher in the east, then finally appears high overhead in the late northern summer and early northern autumn sky.
How to find the Summer Triangle
As night falls in June or July, look east for a sparkling blue-white star. That will be Vega, in Lyra. Reigning at the apex of the celebrated Summer Triangle, Vega is also the brightest of the Summer Triangle’s three stars, which are all bright enough to be seen from many light-polluted cities.
Look to the lower right of Vega to locate the Summer Triangle’s second brightest star. That’s Altair, the brightest star in the constellation Aquila the Eagle. A ruler (12 inches, 30 cm) held at arm’s length fills the gap between these two stars.
Look to the lower left of Vega for another bright star: Deneb, the brightest in the constellation Cygnus the Swan and the third brightest in the Summer Triangle. An outstretched hand at arm’s length approximates the distance from Vega to Deneb.
It’s difficult to convey the huge size of the Summer Triangle. But you’ll see it. These three bright stars – Vega, Deneb and Altair – will become summertime favorites.
Once Cygnus the Swan clears the horizon, you can easily see all of the Summer Triangle asterism. It’s a summertime favorite and easy to see.View at EarthSky Community Photos. | Dr Ski in Valencia, Philippines, captured the Summer Triangle and wrote: “The line between Vega and Altair is broken so as not to obscure the Coathanger Cluster.”
Summer Triangle as a road map to the Milky Way
If you’re lucky enough to be under a dark starry sky on a moonless night, you’ll see the great swath of stars passing between the Summer Triangle’s Vega and Altair. The star Deneb bobs in the middle of this river of stars, which arcs across dark summer skies. This sky river is, of course, the edgewise view into our own Milky Way galaxy. Every star you see with the unaided eye is a member of the Milky Way. And at this time of year, we can see clearly into the galaxy’s flat disk, where most of the stars congregate. By August and September, we will have a good view toward the galaxy’s center.
Once you master the Summer Triangle, you can always locate the Milky Way on a clear, dark night. How about making the most of a dark summer night to explore this band of stars, this starlit boulevard with its celestial delights? Use binoculars to reveal the gossamer beauty of the haunting nebulae and bejeweled star clusters along this starlit trail.
The 3 brightest stars in this image make up the asterism of the Summer Triangle, a giant triangle in the sky composed of the bright stars Vega (top left), Altair (lower middle) and Deneb (far left). Also in this image, under a dark sky and on a moonless night, is the Great Rift that passes right through the Milky Way and the Summer Triangle. Image via NASA/ A. Fujii/ ESA.
Nature’s seasonal calendar
Also, the Summer Triangle serves as a stellar calendar, marking the seasons. So when the stars of the Summer Triangle light up the eastern twilight dusk in middle to late June, it’s a sure sign of the change of seasons, of spring giving way to summer. However, when the Summer Triangle is high in the south to overhead at dusk and early evening, the Summer Triangle’s change of position indicates that summer has ebbed into fall.
A word about asterisms
As we mentioned above, asterisms aren’t constellations; they’re just patterns on the sky’s dome. Constellations generally come to us from ancient times. In the 1930s, the International Astronomical Union officially drew the boundaries of the 88 constellations we recognize today.
Meanwhile, you can make up and name your own asterisms, in much the same way you can recognize shapes in puffy clouds on a summer day.
Of course, some asterisms are so obvious that they’re recognized around the world. And the Summer Triangle is one of these.
Bottom line: On June and July evenings, you’ll find the Summer Triangle in the east at nightfall. It swings high overhead after midnight and sits in the west at daybreak.
View at EarthSky Community Photos | Christy Mandeville in Indian Shores, Florida, captured this dramatic sunset at 8:24 p.m. on June 8, 2022. Christy wrote: “The little boy in the photo kept running around me as I was trying to capture the perfect sunset photo. After I went through the hundreds of photos I captured, I had no idea that he was in any of them! This one stood out.” Thank you, Christy! The latest sunsets follow the summer solstice. Read more below.
Latest sunsets after summer solstice
For the Northern Hemisphere: Your latest sunsets – and latest evening twilights – are happening around now. They always come in late June and early July. Meanwhile, the Northern Hemisphere’s longest day falls on the June 20 solstice.
For 40 degrees north (Philadelphia, Pennsylvania; just north of Denver, Colorado; Beijing, China; Turkey; Japan and Spain), the latest sunsets are centered around June 27. The year’s latest sunsets always come after the summer solstice. But the exact date of the latest sunset depends on your latitude. Farther north – at Seattle – the latest sunsets happen on dates centered on June 25.
Even farther south – at Mexico City or Hawaii – the latest sunsets are centered on dates in early July.
For the Southern Hemisphere: Your latest sunrises of the year happen in late June and early July.
For the Northern or Southern Hemispheres: Latest sunsets go hand-in-hand with your latest twilights. The latest twilights of the year for 40 degrees north also happen in late June and early July. More about twilight below.
View at EarthSky Community Photos. | Cecille Kennedy of Depoe Bay, Oregon, captured this image on May 23, 2023, and wrote: “Sunset on the Pacific Ocean. Clear skies! Except for the marine cloud layer over the ocean horizon. In a few moments the sun would be behind the marine clouds.” Thank you, Cecille!
Why latest sunsets follow summer solstice
The latest sunsets come after the summer solstice because the day is more than 24 hours long at this time of the year.
For several weeks, around the June solstice, the day (as measured by successive returns of the midday sun) is nearly 1/4 minute longer than 24 hours. Hence, the midday sun (solar noon) comes later by the clock in late June than it does on the June solstice. Therefore, the sunrise and sunset times also come later by the clock, as the table below helps to explain.
Chart data via Timeanddate.com.View at EarthSky Community Photos. | Mandy Daniels of Derbyshire, United Kingdom, captured this image on May 23, 2023, and wrote: “The sky just after sunset, looking north and west from my garden.” Thank you, Mandy!
Clock time and sun time
If the Earth’s axis stood upright as our world circled the sun, and if, in addition, the Earth stayed the same distance from the sun all year long, then clock time and sun time would always agree.
However, the Earth’s axis is tilted 23.44 degrees out of vertical, and our distance from the sun varies by about 3 million miles (5 million km) throughout the year. At and around the equinoxes, solar days are shorter than 24 hours, yet at the solstices, solar days are longer than 24 hours.
That’s why the latest sunsets always come on or near June 27 at mid-northern latitudes every year.
At mid-northern latitudes, the later clock time for solar noon one week after the summer solstice is more substantial than the change in daylight hours. Given that the daylight hours on June 27 are almost the same as they are on the June 20-21 solstice, the later clock time for the June 27 solar noon gives us slightly later sunrise and sunset times, as well.
A word about twilight
There are three kinds of twilight:
Civil twilight starts at sundown and ends when the sun is 6 degrees below the horizon.
Nautical twilight occurs when the sun is 6 to 12 degrees below the horizon.
Astronomical twilight happens when the sun is 12 to 18 degrees below the horizon.
North of 50 degrees north latitude, there’s no true night in the month of June. In June, that far north, the sun never gets far enough below the horizon for true night to occur. So from 50 degrees north latitude – to the Arctic Circle (66.5 degrees north latitude) – you’ll find midnight twilight at this time of the year.
And, above the Arctic Circle to the North Pole (90 degrees north latitude), this time of the year is the time of the midnight sun.
Skywatchers learn to recognize the subtle gradations of twilight. True night doesn’t begin until the sun sinks 18 degrees beneath the horizon. North of 50 degrees north latitude, there is no true night in June because the sun never gets far enough below the horizon. Visit Sunrise Sunset Calendars for the times of civil, nautical and astronomical twilight in your sky. Image via Wikimedia Commons/ CC BY-SA 3.0.
Bottom line: Why don’t the latest sunsets come on the longest day (the solstice)? In a nutshell, it’s a discrepancy between the sun and the clock. Thus, for mid-northern latitudes, the latest sunsets always come in late June.
View at EarthSky Community Photos | Christy Mandeville in Indian Shores, Florida, captured this dramatic sunset at 8:24 p.m. on June 8, 2022. Christy wrote: “The little boy in the photo kept running around me as I was trying to capture the perfect sunset photo. After I went through the hundreds of photos I captured, I had no idea that he was in any of them! This one stood out.” Thank you, Christy! The latest sunsets follow the summer solstice. Read more below.
Latest sunsets after summer solstice
For the Northern Hemisphere: Your latest sunsets – and latest evening twilights – are happening around now. They always come in late June and early July. Meanwhile, the Northern Hemisphere’s longest day falls on the June 20 solstice.
For 40 degrees north (Philadelphia, Pennsylvania; just north of Denver, Colorado; Beijing, China; Turkey; Japan and Spain), the latest sunsets are centered around June 27. The year’s latest sunsets always come after the summer solstice. But the exact date of the latest sunset depends on your latitude. Farther north – at Seattle – the latest sunsets happen on dates centered on June 25.
Even farther south – at Mexico City or Hawaii – the latest sunsets are centered on dates in early July.
For the Southern Hemisphere: Your latest sunrises of the year happen in late June and early July.
For the Northern or Southern Hemispheres: Latest sunsets go hand-in-hand with your latest twilights. The latest twilights of the year for 40 degrees north also happen in late June and early July. More about twilight below.
View at EarthSky Community Photos. | Cecille Kennedy of Depoe Bay, Oregon, captured this image on May 23, 2023, and wrote: “Sunset on the Pacific Ocean. Clear skies! Except for the marine cloud layer over the ocean horizon. In a few moments the sun would be behind the marine clouds.” Thank you, Cecille!
Why latest sunsets follow summer solstice
The latest sunsets come after the summer solstice because the day is more than 24 hours long at this time of the year.
For several weeks, around the June solstice, the day (as measured by successive returns of the midday sun) is nearly 1/4 minute longer than 24 hours. Hence, the midday sun (solar noon) comes later by the clock in late June than it does on the June solstice. Therefore, the sunrise and sunset times also come later by the clock, as the table below helps to explain.
Chart data via Timeanddate.com.View at EarthSky Community Photos. | Mandy Daniels of Derbyshire, United Kingdom, captured this image on May 23, 2023, and wrote: “The sky just after sunset, looking north and west from my garden.” Thank you, Mandy!
Clock time and sun time
If the Earth’s axis stood upright as our world circled the sun, and if, in addition, the Earth stayed the same distance from the sun all year long, then clock time and sun time would always agree.
However, the Earth’s axis is tilted 23.44 degrees out of vertical, and our distance from the sun varies by about 3 million miles (5 million km) throughout the year. At and around the equinoxes, solar days are shorter than 24 hours, yet at the solstices, solar days are longer than 24 hours.
That’s why the latest sunsets always come on or near June 27 at mid-northern latitudes every year.
At mid-northern latitudes, the later clock time for solar noon one week after the summer solstice is more substantial than the change in daylight hours. Given that the daylight hours on June 27 are almost the same as they are on the June 20-21 solstice, the later clock time for the June 27 solar noon gives us slightly later sunrise and sunset times, as well.
A word about twilight
There are three kinds of twilight:
Civil twilight starts at sundown and ends when the sun is 6 degrees below the horizon.
Nautical twilight occurs when the sun is 6 to 12 degrees below the horizon.
Astronomical twilight happens when the sun is 12 to 18 degrees below the horizon.
North of 50 degrees north latitude, there’s no true night in the month of June. In June, that far north, the sun never gets far enough below the horizon for true night to occur. So from 50 degrees north latitude – to the Arctic Circle (66.5 degrees north latitude) – you’ll find midnight twilight at this time of the year.
And, above the Arctic Circle to the North Pole (90 degrees north latitude), this time of the year is the time of the midnight sun.
Skywatchers learn to recognize the subtle gradations of twilight. True night doesn’t begin until the sun sinks 18 degrees beneath the horizon. North of 50 degrees north latitude, there is no true night in June because the sun never gets far enough below the horizon. Visit Sunrise Sunset Calendars for the times of civil, nautical and astronomical twilight in your sky. Image via Wikimedia Commons/ CC BY-SA 3.0.
Bottom line: Why don’t the latest sunsets come on the longest day (the solstice)? In a nutshell, it’s a discrepancy between the sun and the clock. Thus, for mid-northern latitudes, the latest sunsets always come in late June.
New research says that large wildfires create weather that is inducive to more fire activity, thus exacerbating the problem. Image via Malachi Brooks/ Unsplash.
Wildfires and weather
Many studies have demonstrated links between global warming and longer and more active fire seasons. But a team of researchers from the University of California, Riverside, looked at a kind of reverse: how wildfires can influence local weather. On June 18, 2024, the researchers said large fires create hotter and drier weather than usual, resulting in a vicious loop of conditions favorable to more fire. Lead author James Gomez said:
It appears these fires are creating their own fire weather.
The researchers published their study in the peer-reviewed journal Atmospheric Chemistry and Physics on June 14, 2024.
Peak fire days
The researchers looked at peak fire days over the past 20 years. They mostly analyzed Northern California, which has had the most intense fires of that U.S. state thanks in part to dense vegetation. The researchers especially zeroed in on days with lower temperatures and higher humidity. Gomez said:
I looked at abnormally cool or wet days during fire season, both with and without fires. This mostly takes out the fire weather effects.
What they found was large fires made those days hotter and drier. And extra heat and arid conditions meant better conditions for more fire. Overall, temperatures were about 1 degree Celsius (1.8 F) warmer on fire days.
This pyrocumulus, or flammagenitus, cloud resulted from a wildfire in California. Clouds resulting from wildfires contain lots of black soot, which traps heat and dries the atmosphere. Image via EllsworthC/ Wikimedia Commons.
Clouds of black soot
When wildfires burn, they create pyrocumulus (or flammagenitus) clouds. These clouds contain lots of ash or dark soot, giving them a darker color than other clouds. And that darker color means they absorb sunlight more readily than traditional clouds. So, this soot traps heat. The trapped heat reduces humidity in the air, which makes it harder for other clouds – the kind that might bring rain – to form. These particles emitted by wildfires – largely black carbon – are absorptive aerosols.
Gomez said:
I wanted to learn how the weather is affected by aerosols emitted by wildfires as they’re burning.
And the discovery is that wildfires are limiting other clouds and the possibility of rain. Gomez said:
What I found is that the black carbon emitted from these California wildfires is not increasing the number of clouds. It’s hydrophobic.
The study also found that slower fire days had less of an effect on the weather. To combat large wildfires brining more fire weather, smaller, more frequent fires is one solution. Gomez said:
There is a buildup of vegetation here in California. We need to allow more frequent small fires to reduce the amount of fuel available to burn. With more forest management and more prescribed burns, we could have fewer giant fires. That is in our control.
Bottom line: Large wildfires create fire weather, resulting in a vicious loop. The fires create dark clouds of soot that increase temperatures and dry out the atmosphere.
New research says that large wildfires create weather that is inducive to more fire activity, thus exacerbating the problem. Image via Malachi Brooks/ Unsplash.
Wildfires and weather
Many studies have demonstrated links between global warming and longer and more active fire seasons. But a team of researchers from the University of California, Riverside, looked at a kind of reverse: how wildfires can influence local weather. On June 18, 2024, the researchers said large fires create hotter and drier weather than usual, resulting in a vicious loop of conditions favorable to more fire. Lead author James Gomez said:
It appears these fires are creating their own fire weather.
The researchers published their study in the peer-reviewed journal Atmospheric Chemistry and Physics on June 14, 2024.
Peak fire days
The researchers looked at peak fire days over the past 20 years. They mostly analyzed Northern California, which has had the most intense fires of that U.S. state thanks in part to dense vegetation. The researchers especially zeroed in on days with lower temperatures and higher humidity. Gomez said:
I looked at abnormally cool or wet days during fire season, both with and without fires. This mostly takes out the fire weather effects.
What they found was large fires made those days hotter and drier. And extra heat and arid conditions meant better conditions for more fire. Overall, temperatures were about 1 degree Celsius (1.8 F) warmer on fire days.
This pyrocumulus, or flammagenitus, cloud resulted from a wildfire in California. Clouds resulting from wildfires contain lots of black soot, which traps heat and dries the atmosphere. Image via EllsworthC/ Wikimedia Commons.
Clouds of black soot
When wildfires burn, they create pyrocumulus (or flammagenitus) clouds. These clouds contain lots of ash or dark soot, giving them a darker color than other clouds. And that darker color means they absorb sunlight more readily than traditional clouds. So, this soot traps heat. The trapped heat reduces humidity in the air, which makes it harder for other clouds – the kind that might bring rain – to form. These particles emitted by wildfires – largely black carbon – are absorptive aerosols.
Gomez said:
I wanted to learn how the weather is affected by aerosols emitted by wildfires as they’re burning.
And the discovery is that wildfires are limiting other clouds and the possibility of rain. Gomez said:
What I found is that the black carbon emitted from these California wildfires is not increasing the number of clouds. It’s hydrophobic.
The study also found that slower fire days had less of an effect on the weather. To combat large wildfires brining more fire weather, smaller, more frequent fires is one solution. Gomez said:
There is a buildup of vegetation here in California. We need to allow more frequent small fires to reduce the amount of fuel available to burn. With more forest management and more prescribed burns, we could have fewer giant fires. That is in our control.
Bottom line: Large wildfires create fire weather, resulting in a vicious loop. The fires create dark clouds of soot that increase temperatures and dry out the atmosphere.
