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.
The Great Rift is the name for a long swath of gaseous clouds, darkening a stretch of the starry band of the Milky Way in our sky.
The Milky Way is the edgewise view into our home galaxy. It has an estimated 100 to 400 billion stars. So why is this area dark? It’s a region of vast star-forming clouds.
You need a dark sky to see the Great Rift. But if you do see it, know that new stars are being born there, shrouded in their gas-and-dust cocoons.
The Great Rift: How to see it
August – at a time when the moon is gone from the evening sky – is an ideal time to look for the Great Rift, or Dark Rift, in the starry band of the Milky Way. Under a dark sky, far from city lights, the Milky Way is easy to see at this time of year, stretching across the sky. The Great Rift appears as dark lanes of dust running the length of the starlit Milky Way band.
You can see the Milky Way most easily in the evening from around June or July through about October. From a Northern Hemisphere location, you’ll see the thickest part of the Milky Way above the southern horizon. From the Southern Hemisphere, the thickest part of the Milky Way appears more overhead.
Notice that the Milky Way band looks milky white: hence, its name. The skies aren’t black like ink between stars in the Milky Way. You’ll know when you see the Great Rift. That’s because it looks as if someone took a marker and colored parts of the Milky Way darker.
View larger. | The Great Rift of the Milky Way passes through the constellation Cassiopeia and the Summer Triangle. Image via Wikimedia (CC BY-SA 3.0).
Constellations along the Great Rift
The Great Rift begins just above the constellation Sagittarius the Archer. Follow the Milky Way up until you see a black area in the Milky Way, just before you get to the constellation Cygnus the Swan. Cygnus is shaped like a cross. Deneb is the brightest star in Cygnus and part of the famous Summer Triangle asterism. You can see the Great Rift inside the Summer Triangle.
Be sure to keep your binoculars handy for any Milky Way viewing session. There are many interesting star-forming regions, star clusters and millions of stars that will capture your attention.
View at EarthSky Community Photos. | William Mathe made the 100-mile (160 km) drive to Last Chance, Colorado, for this scene on March 16, 2024. William wrote: “The ranch house is a bit of a fixer-upper. But it has spectacular views of the core of our little Milky Way galaxy.” Thank you, William!
The Great Rift is dark due to dust
Stars are formed from great clouds of gas and dust in our Milky Way galaxy and other galaxies. When we look up at the starry band of the Milky Way and see the Great Rift, we are looking into our galaxy’s star-forming regions. Imagine the vast number of new stars that will emerge, in time, from these clouds of dust.
Here’s the interaction between interstellar dust in the Milky Way and the structure of our galaxy’s magnetic field, as detected by ESA’s Planck satellite over the entire sky. Image via ESA.
Ancient cultures focused on dark areas, not light areas
You know those paintings where if you look at the light areas you see one thing, but in the dark areas you see something else?
The Great Rift is a bit like that. A few ancient cultures in Central and South America saw the dark areas of the Milky Way as constellations. These dark constellations had a variety of myths associated with them. For example, one important dark constellation was Yacana the Llama. It rises above Cuzco, the ancient city of the Incas, every year in November.
By the way, the other famous area of the sky that is obscured by molecular dust is visible from the Southern Hemisphere. It’s the famous Coalsack Nebula near the Southern Cross, also known as the constellation Crux. The Coalsack is another region of star-forming activity in our night sky, much like the Great Rift.
Bottom line: The Great Rift or Dark Rift is a darkened swath of the Milky Way where new stars are forming. It’s best seen from a rural location away from light pollution.
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.
The Great Rift is the name for a long swath of gaseous clouds, darkening a stretch of the starry band of the Milky Way in our sky.
The Milky Way is the edgewise view into our home galaxy. It has an estimated 100 to 400 billion stars. So why is this area dark? It’s a region of vast star-forming clouds.
You need a dark sky to see the Great Rift. But if you do see it, know that new stars are being born there, shrouded in their gas-and-dust cocoons.
The Great Rift: How to see it
August – at a time when the moon is gone from the evening sky – is an ideal time to look for the Great Rift, or Dark Rift, in the starry band of the Milky Way. Under a dark sky, far from city lights, the Milky Way is easy to see at this time of year, stretching across the sky. The Great Rift appears as dark lanes of dust running the length of the starlit Milky Way band.
You can see the Milky Way most easily in the evening from around June or July through about October. From a Northern Hemisphere location, you’ll see the thickest part of the Milky Way above the southern horizon. From the Southern Hemisphere, the thickest part of the Milky Way appears more overhead.
Notice that the Milky Way band looks milky white: hence, its name. The skies aren’t black like ink between stars in the Milky Way. You’ll know when you see the Great Rift. That’s because it looks as if someone took a marker and colored parts of the Milky Way darker.
View larger. | The Great Rift of the Milky Way passes through the constellation Cassiopeia and the Summer Triangle. Image via Wikimedia (CC BY-SA 3.0).
Constellations along the Great Rift
The Great Rift begins just above the constellation Sagittarius the Archer. Follow the Milky Way up until you see a black area in the Milky Way, just before you get to the constellation Cygnus the Swan. Cygnus is shaped like a cross. Deneb is the brightest star in Cygnus and part of the famous Summer Triangle asterism. You can see the Great Rift inside the Summer Triangle.
Be sure to keep your binoculars handy for any Milky Way viewing session. There are many interesting star-forming regions, star clusters and millions of stars that will capture your attention.
View at EarthSky Community Photos. | William Mathe made the 100-mile (160 km) drive to Last Chance, Colorado, for this scene on March 16, 2024. William wrote: “The ranch house is a bit of a fixer-upper. But it has spectacular views of the core of our little Milky Way galaxy.” Thank you, William!
The Great Rift is dark due to dust
Stars are formed from great clouds of gas and dust in our Milky Way galaxy and other galaxies. When we look up at the starry band of the Milky Way and see the Great Rift, we are looking into our galaxy’s star-forming regions. Imagine the vast number of new stars that will emerge, in time, from these clouds of dust.
Here’s the interaction between interstellar dust in the Milky Way and the structure of our galaxy’s magnetic field, as detected by ESA’s Planck satellite over the entire sky. Image via ESA.
Ancient cultures focused on dark areas, not light areas
You know those paintings where if you look at the light areas you see one thing, but in the dark areas you see something else?
The Great Rift is a bit like that. A few ancient cultures in Central and South America saw the dark areas of the Milky Way as constellations. These dark constellations had a variety of myths associated with them. For example, one important dark constellation was Yacana the Llama. It rises above Cuzco, the ancient city of the Incas, every year in November.
By the way, the other famous area of the sky that is obscured by molecular dust is visible from the Southern Hemisphere. It’s the famous Coalsack Nebula near the Southern Cross, also known as the constellation Crux. The Coalsack is another region of star-forming activity in our night sky, much like the Great Rift.
Bottom line: The Great Rift or Dark Rift is a darkened swath of the Milky Way where new stars are forming. It’s best seen from a rural location away from light pollution.
A heat burst is a sudden surge of heat and powerful winds. This unpredictable phenomenon caught people by surprise on the tropical coast of Granada, in southern Spain, on Sunday afternoon. The event created 15 minutes of chaos.
Heat burst hits Granada in Spain
On Sunday, August 17, 2025, a sudden and extremely violent weather event surprised residents and beachgoers along Granada’s Costa Tropical, in Spain. Around 7:50 p.m. local time, in towns such as Motril, Salobreña and Torrenueva, a heat burst occurred, causing a rapid temperature spike up to 104.2°F (40.1°C), accompanied by strong wind gusts reaching 53.9 miles per hour (86.8 kilometers per hour). Within minutes, the beach turned into a chaotic scene: the winds launched umbrellas and personal belongings through the air, tore awnings apart and uprooted palm trees. In addition, a waterspout — a kind of tornado over the sea — formed just off the coast.
Due to the sudden violence of the phenomenon, authorities evacuated the beaches as a precaution. The 112 emergency service received numerous calls about flying objects and people in distress in the water. Maritime Rescue teams, the Civil Guard and lifeguards responded quickly, managing to rescue five swimmers who had been dragged out to sea by the strong waves and wind. Fortunately, there were no fatalities, although there was considerable material damage and widespread alarm.
This extreme episode highlighted a weather phenomenon still largely unknown to much of the public: the heat burst.
What are heat bursts?
A heat burst is a rare but potentially dangerous meteorological event. It occurs when a mass of air suddenly descends from high levels of the atmosphere. As it falls, the air passes through dry atmospheric layers, causing it to heat up through compression. Upon reaching the ground, it expands violently in all directions, leading to a rapid temperature increase, a sudden drop in humidity and strong gusts of wind.
These winds, which can exceed 49 or even 62 mph (80 or 100 kph), usually last only a few minutes. But they have a localized and unpredictable impact, so they’re extremely difficult to detect or forecast. Their arrival can catch the population completely off guard.
The phenomenon tends to occur in the late afternoon or evening. That’s when there is atmospheric instability at higher levels and a layer of dry air at mid-levels. It’s more common in inland areas or coastal mountain regions, such as Granada’s Costa Tropical, where the terrain favors the acceleration of these descending air currents.
A heat burst happens when a dying thunderstorm sends air down through a hot, dry layer in the atmosphere. As the air falls, it dries out and heats up quickly, reaching the ground as a sudden burst of hot, dry wind. Image via Wikipedia (Public domain).
Consequences of the heat burst in Granada
The heat burst on August 17 left a visible mark on several parts of the Granada coastline. The beaches, which were packed with visitors due to the summer weekend, had to be evacuated within minutes. Strong gusts of wind snapped palm trees, moved inflatable pools, destroyed furniture and caused major disturbances at sea.
In Torrenueva, the formation of a waterspout triggered additional panic among beachgoers, who saw the water swirling menacingly near the coast. Emergency services responded swiftly, rescuing three people near La Joya beach and two others who were brought to the port of Motril by a private boat after being swept out to sea.
Local authorities advised people to stay indoors during the heat burst and reinforced lifeguard services. A damage assessment operation confirmed the scale of the impact: fallen trees, damaged vehicles, destroyed materials and a large amount of debris scattered by the wind.
Vendaval en Motril . El reventón térmico que ha dejado toda la Costa Tropical con vientos huracanados pic.twitter.com/zhL8mpOq4Y
Even heavy objects blew away in the heat burst. It ripped awnings from walls and uprooted trees. People evacuated the beaches of Salobreña, Torrenueva and Motril and took shelter indoors.
What can we do when heat bursts strike?
Although these events are difficult to predict with precision, experts stress the importance of understanding them and being prepared. Heat bursts, despite their short duration, can have devastating effects in highly localized areas. Having evacuation protocols in place, improving weather alert systems and reinforcing beach surveillance on extremely hot days can make the difference between a controlled situation and a tragedy.
Severe heat events, such as heat bursts, are becoming more common with climate change. So, public awareness and institutional preparedness will be key to responding effectively to similar events in the future.
During the Granada heat burst, several people paddle surfing called for help as the wind dragged them away from shore. Thanks to the heroes aboard motorboats and jet skis, these lives were saved. Emergency services also rescued 3 people who ended up adrift, and a private boat saved 2 more. Despite the short duration of the event, many people will likely remember the chaos for a long time.
Bottom line: Have you heard of a heat burst? It happens when a spike in temperatures and strong winds hit a localized area. Read about the heat burst in Granada, Spain, on Sunday.
A heat burst is a sudden surge of heat and powerful winds. This unpredictable phenomenon caught people by surprise on the tropical coast of Granada, in southern Spain, on Sunday afternoon. The event created 15 minutes of chaos.
Heat burst hits Granada in Spain
On Sunday, August 17, 2025, a sudden and extremely violent weather event surprised residents and beachgoers along Granada’s Costa Tropical, in Spain. Around 7:50 p.m. local time, in towns such as Motril, Salobreña and Torrenueva, a heat burst occurred, causing a rapid temperature spike up to 104.2°F (40.1°C), accompanied by strong wind gusts reaching 53.9 miles per hour (86.8 kilometers per hour). Within minutes, the beach turned into a chaotic scene: the winds launched umbrellas and personal belongings through the air, tore awnings apart and uprooted palm trees. In addition, a waterspout — a kind of tornado over the sea — formed just off the coast.
Due to the sudden violence of the phenomenon, authorities evacuated the beaches as a precaution. The 112 emergency service received numerous calls about flying objects and people in distress in the water. Maritime Rescue teams, the Civil Guard and lifeguards responded quickly, managing to rescue five swimmers who had been dragged out to sea by the strong waves and wind. Fortunately, there were no fatalities, although there was considerable material damage and widespread alarm.
This extreme episode highlighted a weather phenomenon still largely unknown to much of the public: the heat burst.
What are heat bursts?
A heat burst is a rare but potentially dangerous meteorological event. It occurs when a mass of air suddenly descends from high levels of the atmosphere. As it falls, the air passes through dry atmospheric layers, causing it to heat up through compression. Upon reaching the ground, it expands violently in all directions, leading to a rapid temperature increase, a sudden drop in humidity and strong gusts of wind.
These winds, which can exceed 49 or even 62 mph (80 or 100 kph), usually last only a few minutes. But they have a localized and unpredictable impact, so they’re extremely difficult to detect or forecast. Their arrival can catch the population completely off guard.
The phenomenon tends to occur in the late afternoon or evening. That’s when there is atmospheric instability at higher levels and a layer of dry air at mid-levels. It’s more common in inland areas or coastal mountain regions, such as Granada’s Costa Tropical, where the terrain favors the acceleration of these descending air currents.
A heat burst happens when a dying thunderstorm sends air down through a hot, dry layer in the atmosphere. As the air falls, it dries out and heats up quickly, reaching the ground as a sudden burst of hot, dry wind. Image via Wikipedia (Public domain).
Consequences of the heat burst in Granada
The heat burst on August 17 left a visible mark on several parts of the Granada coastline. The beaches, which were packed with visitors due to the summer weekend, had to be evacuated within minutes. Strong gusts of wind snapped palm trees, moved inflatable pools, destroyed furniture and caused major disturbances at sea.
In Torrenueva, the formation of a waterspout triggered additional panic among beachgoers, who saw the water swirling menacingly near the coast. Emergency services responded swiftly, rescuing three people near La Joya beach and two others who were brought to the port of Motril by a private boat after being swept out to sea.
Local authorities advised people to stay indoors during the heat burst and reinforced lifeguard services. A damage assessment operation confirmed the scale of the impact: fallen trees, damaged vehicles, destroyed materials and a large amount of debris scattered by the wind.
Vendaval en Motril . El reventón térmico que ha dejado toda la Costa Tropical con vientos huracanados pic.twitter.com/zhL8mpOq4Y
Even heavy objects blew away in the heat burst. It ripped awnings from walls and uprooted trees. People evacuated the beaches of Salobreña, Torrenueva and Motril and took shelter indoors.
What can we do when heat bursts strike?
Although these events are difficult to predict with precision, experts stress the importance of understanding them and being prepared. Heat bursts, despite their short duration, can have devastating effects in highly localized areas. Having evacuation protocols in place, improving weather alert systems and reinforcing beach surveillance on extremely hot days can make the difference between a controlled situation and a tragedy.
Severe heat events, such as heat bursts, are becoming more common with climate change. So, public awareness and institutional preparedness will be key to responding effectively to similar events in the future.
During the Granada heat burst, several people paddle surfing called for help as the wind dragged them away from shore. Thanks to the heroes aboard motorboats and jet skis, these lives were saved. Emergency services also rescued 3 people who ended up adrift, and a private boat saved 2 more. Despite the short duration of the event, many people will likely remember the chaos for a long time.
Bottom line: Have you heard of a heat burst? It happens when a spike in temperatures and strong winds hit a localized area. Read about the heat burst in Granada, Spain, on Sunday.
People have frequently spotted whales and dolphins together in the ocean. But, are they actually playing together, or is it more of a one-sided relationship?
Do whales and dolphins play together?
While it’s common for people to see whales and dolphins interacting, scientists have done few studies on this behavior. When you see the animals together, you can’t help but wonder: Do both animals want to socialize, is one trying to avoid the other, or are they being aggressive toward each other? Scientists from Griffith University in Australia said on August 12, 2025, that they’ve analyzed interactions between 19 species of baleen whales and dolphins in 17 locations around the world. And, according to their study, one-quarter of these interactions are mutual. So what happens in the rest of the cases? Which species are the most social and playful?
The scientists published their peer-reviewed study in the journal Discover Animals on August 12, 2025.
Dolphins initiate the interactions
In the scientific community, it is widely acknowledged that dolphins are sociable, playful and curious, and that baleen whales are not only friendly but also have excellent communication skills. Thus, dolphins are usually the ones who initiate interactions with the peaceful whales. But sometimes they can be a bit too playful. According to the study’s lead author, Olaf Meynecke of Griffith University:
We were particularly interested in documenting the whales’ reactions and responses toward the dolphins, as commonly dolphins are described to harass and annoy the whales.
The study analyzed 199 separate and unrelated interactions between whales and dolphins. Photos and videos from the public, tour guides and members of the scientific community made the analysis possible. Contrary to initial assumptions, it turns out that in most cases, the whales did not avoid the dolphins. Meynecke notes:
The vast majority of the observed interactions did not show avoidance behavior.
In particular, humpback whales seem to be the most sociable. The evidence that whales don’t reject interactions with dolphins lies in their body language. According to Meynecke:
In particular, for humpback whales, we found that for one-third of the events the behavioral responses toward the dolphins appear positive. The humpback whales were rolling from side to side, undertaking belly presentation and other behaviors that are associated with courtship or friendly socializing.
Body sections of a whale and dolphin positions used to categorize whale and dolphin interactions. Image via Discover Animals (Used with permission).
Body language says it all
Whales communicate in many ways. Humpback whales express themselves through clicks, songs, fin slaps and breaching. And each of these sounds and movements means something. For example, when they roll from side to side and expose sensitive areas such as their bellies, this indicates they feel comfortable among other members of their species or other animals. However, a slap of the tail against the water is a warning.
Of course, there are many details to take into account, which is why the scientists conducted a thorough analysis. During each interaction, the researchers recorded the whale and dolphin species, the date and time of the event, the location, the number of animals involved, their ages and the relative position of the dolphins in relation to key parts of the whale’s body (head, flank and tail fluke).
The most common interaction between whales and dolphins consisted of dolphins swimming and jumping near the whale’s head. It’s similar to how dolphins behave around boats (called bow riding). This could suggest a form of one-sided play on the part of the dolphins. However, Meynecke said:
Whales also strategically moved slowly in the direction of the dolphins with their head and rostrum.
A variety of whale and dolphin interactions. A) Bottlenose dolphin in proximity to a humpback whale rostrum, bow riding near the Gold Coast, Australia. B) A bottle nose dolphin close to a pectoral fin of a humpback whale at Bermagui, Australia. C) Petting or rubbing of a common dolphin on the rostrum of a fin whale in the Celtic Sea, England. D) A group of bottlenose dolphins swimming alongside a southern right whale that is moving its fluke toward the dolphins in Esperance, Australia. Images via A) Roving Media; B) WildLive.Media; C) Dan Abbott; D) Jaimen Hudson/ Discover Animals.
Which species interact the most?
In total, scientists recorded dolphin interactions with 425 baleen whales from six different species. Humpback whales were the most frequent, making up 68% of encounters, followed by gray whales at 16% and fin whales at 7%.
As for the dolphins, scientists estimated around 1,570 individuals. Bottlenose dolphins were the most numerous (51%), followed by common dolphins (17%) and Pacific white-sided dolphins (15%).
Most of the interactions involved adult specimens, although they also documented calves. They saw whale calves in 44 instances and dolphin calves in 53. In 21 events, calves of both species were present at the same time.
Each whale species showed different responses to the presence of dolphins. Humpback whales, for example, moved their pectoral fins toward them 172 times. Gray whales frequently rolled over (56 times), while southern right whales performed fin slaps in five out of 10 recorded encounters.
Physically aggressive behaviors, such as tail slaps (observed 18 times) or head butts (not observed), were rare among humpback whales.
Additionally, in two recordings obtained from suction-cup cameras attached to humpback whales, researchers observed bottlenose dolphins following the whales both at the surface and deep underwater, staying close and possibly engaging in playful or social interaction.
Here’s a bottlenose dolphin interacting with humpback whales off the Australian coast in an action called “bow-riding”. Image via Roving media/ Griffith University.
The importance of behavior studies
Dolphins are highly social, playful and curious animals. They have a natural tendency to explore their environment and interact with other marine species, including whales. Whales, especially the larger ones like humpbacks or blues, are typically more passive or slower compared to dolphins. Their behavior is generally more reserved, and they focus their energy on activities such as migration or feeding. Meynecke said:
While social play is cooperative and reciprocal, there is also one-sided play or interaction, with only one participant perceiving the interaction as playful, as seen in cases of teasing or harassment by dolphins during feeding events.
And, just like dolphins, humans are curious, too. We want to know more about whales and dolphins, swim among them, photograph them…. In simple terms, we also want to interact. Meynecke added:
Behavioral studies of marine mammals such as these provide insight into their complex social structures, play a crucial role in enhancing our understanding of marine ecosystems and the interactions among marine species.
When you’re out on the water, you often see whales and dolphins interacting, and as a scientist, you can’t help but wonder why.
I hope that this study can serve as a foundation for future studies.
As curious and sociable mammals ourselves, it’s normal we want to know more about how other animals interact with each other. Here’s a fin whale with bow-riding dolphins off the coast of England. Image via Dan Abbott/ Griffith Univerity.
Bottom line: Scientists observed whales and dolphins together to study their interactions. In most cases, whales do not avoid dolphins and their body language shows they sometimes socialize with them.
People have frequently spotted whales and dolphins together in the ocean. But, are they actually playing together, or is it more of a one-sided relationship?
Do whales and dolphins play together?
While it’s common for people to see whales and dolphins interacting, scientists have done few studies on this behavior. When you see the animals together, you can’t help but wonder: Do both animals want to socialize, is one trying to avoid the other, or are they being aggressive toward each other? Scientists from Griffith University in Australia said on August 12, 2025, that they’ve analyzed interactions between 19 species of baleen whales and dolphins in 17 locations around the world. And, according to their study, one-quarter of these interactions are mutual. So what happens in the rest of the cases? Which species are the most social and playful?
The scientists published their peer-reviewed study in the journal Discover Animals on August 12, 2025.
Dolphins initiate the interactions
In the scientific community, it is widely acknowledged that dolphins are sociable, playful and curious, and that baleen whales are not only friendly but also have excellent communication skills. Thus, dolphins are usually the ones who initiate interactions with the peaceful whales. But sometimes they can be a bit too playful. According to the study’s lead author, Olaf Meynecke of Griffith University:
We were particularly interested in documenting the whales’ reactions and responses toward the dolphins, as commonly dolphins are described to harass and annoy the whales.
The study analyzed 199 separate and unrelated interactions between whales and dolphins. Photos and videos from the public, tour guides and members of the scientific community made the analysis possible. Contrary to initial assumptions, it turns out that in most cases, the whales did not avoid the dolphins. Meynecke notes:
The vast majority of the observed interactions did not show avoidance behavior.
In particular, humpback whales seem to be the most sociable. The evidence that whales don’t reject interactions with dolphins lies in their body language. According to Meynecke:
In particular, for humpback whales, we found that for one-third of the events the behavioral responses toward the dolphins appear positive. The humpback whales were rolling from side to side, undertaking belly presentation and other behaviors that are associated with courtship or friendly socializing.
Body sections of a whale and dolphin positions used to categorize whale and dolphin interactions. Image via Discover Animals (Used with permission).
Body language says it all
Whales communicate in many ways. Humpback whales express themselves through clicks, songs, fin slaps and breaching. And each of these sounds and movements means something. For example, when they roll from side to side and expose sensitive areas such as their bellies, this indicates they feel comfortable among other members of their species or other animals. However, a slap of the tail against the water is a warning.
Of course, there are many details to take into account, which is why the scientists conducted a thorough analysis. During each interaction, the researchers recorded the whale and dolphin species, the date and time of the event, the location, the number of animals involved, their ages and the relative position of the dolphins in relation to key parts of the whale’s body (head, flank and tail fluke).
The most common interaction between whales and dolphins consisted of dolphins swimming and jumping near the whale’s head. It’s similar to how dolphins behave around boats (called bow riding). This could suggest a form of one-sided play on the part of the dolphins. However, Meynecke said:
Whales also strategically moved slowly in the direction of the dolphins with their head and rostrum.
A variety of whale and dolphin interactions. A) Bottlenose dolphin in proximity to a humpback whale rostrum, bow riding near the Gold Coast, Australia. B) A bottle nose dolphin close to a pectoral fin of a humpback whale at Bermagui, Australia. C) Petting or rubbing of a common dolphin on the rostrum of a fin whale in the Celtic Sea, England. D) A group of bottlenose dolphins swimming alongside a southern right whale that is moving its fluke toward the dolphins in Esperance, Australia. Images via A) Roving Media; B) WildLive.Media; C) Dan Abbott; D) Jaimen Hudson/ Discover Animals.
Which species interact the most?
In total, scientists recorded dolphin interactions with 425 baleen whales from six different species. Humpback whales were the most frequent, making up 68% of encounters, followed by gray whales at 16% and fin whales at 7%.
As for the dolphins, scientists estimated around 1,570 individuals. Bottlenose dolphins were the most numerous (51%), followed by common dolphins (17%) and Pacific white-sided dolphins (15%).
Most of the interactions involved adult specimens, although they also documented calves. They saw whale calves in 44 instances and dolphin calves in 53. In 21 events, calves of both species were present at the same time.
Each whale species showed different responses to the presence of dolphins. Humpback whales, for example, moved their pectoral fins toward them 172 times. Gray whales frequently rolled over (56 times), while southern right whales performed fin slaps in five out of 10 recorded encounters.
Physically aggressive behaviors, such as tail slaps (observed 18 times) or head butts (not observed), were rare among humpback whales.
Additionally, in two recordings obtained from suction-cup cameras attached to humpback whales, researchers observed bottlenose dolphins following the whales both at the surface and deep underwater, staying close and possibly engaging in playful or social interaction.
Here’s a bottlenose dolphin interacting with humpback whales off the Australian coast in an action called “bow-riding”. Image via Roving media/ Griffith University.
The importance of behavior studies
Dolphins are highly social, playful and curious animals. They have a natural tendency to explore their environment and interact with other marine species, including whales. Whales, especially the larger ones like humpbacks or blues, are typically more passive or slower compared to dolphins. Their behavior is generally more reserved, and they focus their energy on activities such as migration or feeding. Meynecke said:
While social play is cooperative and reciprocal, there is also one-sided play or interaction, with only one participant perceiving the interaction as playful, as seen in cases of teasing or harassment by dolphins during feeding events.
And, just like dolphins, humans are curious, too. We want to know more about whales and dolphins, swim among them, photograph them…. In simple terms, we also want to interact. Meynecke added:
Behavioral studies of marine mammals such as these provide insight into their complex social structures, play a crucial role in enhancing our understanding of marine ecosystems and the interactions among marine species.
When you’re out on the water, you often see whales and dolphins interacting, and as a scientist, you can’t help but wonder why.
I hope that this study can serve as a foundation for future studies.
As curious and sociable mammals ourselves, it’s normal we want to know more about how other animals interact with each other. Here’s a fin whale with bow-riding dolphins off the coast of England. Image via Dan Abbott/ Griffith Univerity.
Bottom line: Scientists observed whales and dolphins together to study their interactions. In most cases, whales do not avoid dolphins and their body language shows they sometimes socialize with them.
We’ll have a Black Moon on August 22-23, 2025. What’s a Black Moon? It can either be the 2nd new moon in a month or the 3rd new moon in a season with 4 new moons. This upcoming Black Moon is the latter. Join EarthSky’s Deborah Byrd at 12:15 p.m. CDT (17:15 UTC) on August 19, 2025, as she talks about the role of Black Moons in astronomy! Image via Eliot Herman/ EarthSky.
Black Moon coming on August 22-23
When we have two full moons in a single month, we in astronomy call the 2nd one a Blue Moon. That’s a relatively recent name and definition. The folklorist Philip Hiscock traced the modern usage of the term Blue Moon back into the 20th century in a 1999 article. Now, it seems, journalists and astronomy buffs have begun using the name Black Moon for the 2nd new moon in a single month. We have a Black Moon coming up on August 22-23, 2025 … but its definition, though still following the rules for Blue Moons, is slightly different.
That is, a Blue Moon can also be the 3rd of four full moons in a season. And so, apparently, can Black Moons. Who decides these things? We do! It’s folklore, not official astronomy. And that means we, the folk, decide.
So the next Black Moon is August 22-23. Blue Moons and Black Moons follow the same rules. And the modern definition for Blue Moons has been studied by professional folklorists.
But where did the term Black Moon come from?
What is it?
Blue Moons and Black Moons have entirely different histories. Blue Moons stemmed from a mistake in a 1946 article in Sky & Telescope magazine. A writer mistakenly quoted the Old Farmer’s Almanac, calling the 2nd of two full moons in a month a Blue Moon. And, in the 1970s and ’80s, other astronomy writers picked up this 2nd-full-moon-in-a-month definition and popularized it (read about the popularization of Blue Moons in the Hiscock article).
But Black Moons didn’t really make an appearance on the astronomy scene until … well, I’m not sure when … but more recently than Blue Moons.
Still, I can recall reading about Black Moons in Sten Odenwald’s great blog The Astronomy Cafe some decades ago. How many decades? That I couldn’t tell you. I tried to find Sten to ask him, but couldn’t track him down. My recollection is that he said the term Black Moon came from Wiccan culture. And ChatGPT mentioned that connection, too, when I asked it this weekend.
I’m also reading this year – at the StarWalk website – that the expression Black Moon is used when there’s no new moon in a month. We typically do have a full moon and a new moon each month. I had not heard that definition of Black Moon, in all my 50 years of writing about the night sky. But there you go. The folk will have it!
View at EarthSky Community Photos. | Chuck Reinhart captured this starry scene from Vincennes, Indiana, in November 2024. Thank you, Chuck! This dark starry sky is like what you’ll see around a new moon. The 3rd new moon this astronomical season (June solstice to September equinox) – called a Black Moon – will fall on August 22-23, 2025. New moons rise and set with the sun. So nights around the new moon are dark and perfect for stargazing.
When is it?
This 2025 seasonal Black Moon – otherwise known as this month’s new moon – will fall at 6:06 UTC (1:06 a.m. CDT) on August 23. So it might fall on August 22 for you, depending on your time zone. A Black Moon – like any new moon – isn’t visible in Earth’s sky. The moon is new when it’s more or less between the Earth and sun for that monthly orbit. So, at every new moon, the moon travels close in our sky to the sun. For all of Earth, it’s up in daylight and can’t be seen.
But new-moon-time is a great time to stargaze, because without the moon in the sky, the night is darker, and you can see more stars. This is especially true if you venture out to a dark-sky site.
Black Moon fun facts
Monthly Black Moons happen about once every 29 months. That’s the definition of a Black Moon as the 2nd of two new moons in a calendar month.
Seasonal Black Moons happen about once every 33 months. That’s the definition of a Black Moon as the 3rd of four new moons in a season.
The last seasonal Black Moon, prior to this August 2025 Black Moon, was May 19, 2023. And the next one will be August 20, 2028.
The last monthly Black Moon was December 30-31, 2024. And the next monthly Black Moon will be on August 31, 2027.
The name Blue Moon can be misleading. The moon doesn’t appear blue in color during these full moons. But the name Black Moon is slightly more accurate, because you can’t see the moon in the night sky (because it’s up in the daytime!). Also, if you think about the body of the moon itself … its darkened half is facing Earth at the time of new moon.
Cool Black Moon events
We’ll have a super Black Moon on August 20, 2028. It’ll be a new moon nearly coinciding with perigee, the moon’s closest point to Earth for that month. Read about supermoons here.
We’ll have three Black Moons in a row in 2033if you are okay with the definition that no new moon means a Black Moon. In other words, in 2033, the new moon of January 30 and March 30 will be the second in a month. And there will be no new moon in February. That’s a black Moon triple whammy!
A Black Moon really does appear dark from Earth. Its darkened half is facing Earth at that time. But you can’t see a Black Moon. Like any new moon, it travels across the sky with the sun during the day, hidden in the sun’s glare. Image via TimeandDate.com. Used with permission.
Bottom line: We’ll have a Black Moon on August 22-23, 2025. A Black Moon is a special kind of new moon. Learn more about Black Moons here.
We’ll have a Black Moon on August 22-23, 2025. What’s a Black Moon? It can either be the 2nd new moon in a month or the 3rd new moon in a season with 4 new moons. This upcoming Black Moon is the latter. Join EarthSky’s Deborah Byrd at 12:15 p.m. CDT (17:15 UTC) on August 19, 2025, as she talks about the role of Black Moons in astronomy! Image via Eliot Herman/ EarthSky.
Black Moon coming on August 22-23
When we have two full moons in a single month, we in astronomy call the 2nd one a Blue Moon. That’s a relatively recent name and definition. The folklorist Philip Hiscock traced the modern usage of the term Blue Moon back into the 20th century in a 1999 article. Now, it seems, journalists and astronomy buffs have begun using the name Black Moon for the 2nd new moon in a single month. We have a Black Moon coming up on August 22-23, 2025 … but its definition, though still following the rules for Blue Moons, is slightly different.
That is, a Blue Moon can also be the 3rd of four full moons in a season. And so, apparently, can Black Moons. Who decides these things? We do! It’s folklore, not official astronomy. And that means we, the folk, decide.
So the next Black Moon is August 22-23. Blue Moons and Black Moons follow the same rules. And the modern definition for Blue Moons has been studied by professional folklorists.
But where did the term Black Moon come from?
What is it?
Blue Moons and Black Moons have entirely different histories. Blue Moons stemmed from a mistake in a 1946 article in Sky & Telescope magazine. A writer mistakenly quoted the Old Farmer’s Almanac, calling the 2nd of two full moons in a month a Blue Moon. And, in the 1970s and ’80s, other astronomy writers picked up this 2nd-full-moon-in-a-month definition and popularized it (read about the popularization of Blue Moons in the Hiscock article).
But Black Moons didn’t really make an appearance on the astronomy scene until … well, I’m not sure when … but more recently than Blue Moons.
Still, I can recall reading about Black Moons in Sten Odenwald’s great blog The Astronomy Cafe some decades ago. How many decades? That I couldn’t tell you. I tried to find Sten to ask him, but couldn’t track him down. My recollection is that he said the term Black Moon came from Wiccan culture. And ChatGPT mentioned that connection, too, when I asked it this weekend.
I’m also reading this year – at the StarWalk website – that the expression Black Moon is used when there’s no new moon in a month. We typically do have a full moon and a new moon each month. I had not heard that definition of Black Moon, in all my 50 years of writing about the night sky. But there you go. The folk will have it!
View at EarthSky Community Photos. | Chuck Reinhart captured this starry scene from Vincennes, Indiana, in November 2024. Thank you, Chuck! This dark starry sky is like what you’ll see around a new moon. The 3rd new moon this astronomical season (June solstice to September equinox) – called a Black Moon – will fall on August 22-23, 2025. New moons rise and set with the sun. So nights around the new moon are dark and perfect for stargazing.
When is it?
This 2025 seasonal Black Moon – otherwise known as this month’s new moon – will fall at 6:06 UTC (1:06 a.m. CDT) on August 23. So it might fall on August 22 for you, depending on your time zone. A Black Moon – like any new moon – isn’t visible in Earth’s sky. The moon is new when it’s more or less between the Earth and sun for that monthly orbit. So, at every new moon, the moon travels close in our sky to the sun. For all of Earth, it’s up in daylight and can’t be seen.
But new-moon-time is a great time to stargaze, because without the moon in the sky, the night is darker, and you can see more stars. This is especially true if you venture out to a dark-sky site.
Black Moon fun facts
Monthly Black Moons happen about once every 29 months. That’s the definition of a Black Moon as the 2nd of two new moons in a calendar month.
Seasonal Black Moons happen about once every 33 months. That’s the definition of a Black Moon as the 3rd of four new moons in a season.
The last seasonal Black Moon, prior to this August 2025 Black Moon, was May 19, 2023. And the next one will be August 20, 2028.
The last monthly Black Moon was December 30-31, 2024. And the next monthly Black Moon will be on August 31, 2027.
The name Blue Moon can be misleading. The moon doesn’t appear blue in color during these full moons. But the name Black Moon is slightly more accurate, because you can’t see the moon in the night sky (because it’s up in the daytime!). Also, if you think about the body of the moon itself … its darkened half is facing Earth at the time of new moon.
Cool Black Moon events
We’ll have a super Black Moon on August 20, 2028. It’ll be a new moon nearly coinciding with perigee, the moon’s closest point to Earth for that month. Read about supermoons here.
We’ll have three Black Moons in a row in 2033if you are okay with the definition that no new moon means a Black Moon. In other words, in 2033, the new moon of January 30 and March 30 will be the second in a month. And there will be no new moon in February. That’s a black Moon triple whammy!
A Black Moon really does appear dark from Earth. Its darkened half is facing Earth at that time. But you can’t see a Black Moon. Like any new moon, it travels across the sky with the sun during the day, hidden in the sun’s glare. Image via TimeandDate.com. Used with permission.
Bottom line: We’ll have a Black Moon on August 22-23, 2025. A Black Moon is a special kind of new moon. Learn more about Black Moons here.
At greatest elongation on August 19, 2025, Mercury will lie to one side of the sun as seen from Earth. That’s when it’s at its greatest distance from the sun before sunrise on our sky’s dome. Chart via EarthSky.
Mercury farthest from the sunrise on August 19
The innermost planet Mercury orbits the sun every 88 days. And Earth is moving, too. So Mercury goes between us and the sun pretty often, about every 116 days. It did this last at 0 UTC on August 1, 2025, reaching the point astronomers call inferior conjunction. And since then, Mercury has been speeding ahead of Earth in orbit. It re-emerged in our morning sky in early August. Mercury will reach its greatest morning elongation – its greatest apparent distance from the rising sun – on August 19, 2025. Also, brilliant Venus and Jupiter are near Mercury in the morning sky.
Mercury greatest elongation, August 2025
When to watch: Officially, Mercury emerged in early August in the morning sky. Look for it about 30 minutes before sunrise. At greatest elongation – August 19, 2025 – Mercury is farthest from the sunrise on our sky’s dome. And after that, when it’ll be edging back toward the sunrise, it’ll brighten a little bit more, making Mercury easier to spot – although low – in the morning twilight. Where to look: Look in the sunrise direction as the sky is getting lighter. Greatest elongation is on August 19 at 10 UTC (5:00 a.m. CDT). Mercury is shining at magnitude 0 that morning. And it’s 19 degrees from the sun. Through a telescope on and around August 19, Mercury appears 42% illuminated, in a crescent phase, and 7.33 arcseconds across. Note: Once you spot it, notice that Mercury brightens quickly as August progresses, reaching a magnitude of around -1.2 (bright, but competing with the morning twilight) late in August when it will slip away in the morning glare.
By the way, this Mercury elongation – due to the high angle of the ecliptic to the horizon – favors the Northern Hemisphere.
In the meantime, the innermost planet – named for the fleet-footed messenger god of the ancient Romans – will be visible for another week or two, especially from the Northern Hemisphere.
Finder charts for Mercury
In late August, for Northern Hemisphere viewers, brilliant Venus and bright Jupiter will lie near Mercury. Mercury will reach its greatest distance from the morning sun – or greatest western elongation – at 10 UTC on August 19. It will be 19 degrees from the sun then. And Mercury moves from the constellation of Cancer the Crab to Leo the Lion this month. Chart via EarthSky.In late August, for Southern Hemisphere viewers, brilliant Venus and bright Jupiter are near Mercury when it reaches its greatest distance from the sun on August 19. Mercury will lie low in the bright eastern twilight about 30 minutes before sunrise. Chart via EarthSky.
The moon visits Mercury
In the early morning hours on August 21, the thin waning crescent moon will lie below brilliant Venus and bright Jupiter and close to Mercury in the bright twilight. Nearby you’ll spot the bright star Procyon and Gemini’s twin stars, Castor and Pollux. Watch for them before dawn. Chart via EarthSky.
Mercury part of a planet parade
For those with optical aid, there will be 6 planets in the early morning sky the last few weeks of August. And you can see 4 of the planets with your eyes alone. Here’s the view from the Northern Hemisphere. You can catch Venus and Jupiter before dawn and through the brightening twilight. You might spot Mercury hiding in the morning twilight. Saturn is visible most of the night but will fade from view by dawn. To see Uranus and Neptune, you’ll need to use binoculars or a small telescope. Uranus lies between Venus and Saturn. And Neptune lies close to Saturn. The planets are all along the ecliptic, the path the sun travels in the daytime (the green line on our chart). Chart via EarthSky.
For precise sun and Mercury rising times at your location:
Feb 8, 2025: Superior conjunction (passes behind sun from Earth) Mar 8, 2025: Greatest elongation (evening) Mar 24, 2025: Inferior conjunction (races between Earth and sun) Apr 21, 2025: Greatest elongation (morning) May 30, 2025: Superior conjunction (passes behind sun from Earth) Jul 4, 2025: Greatest elongation (evening) Aug 1, 2025: Inferior conjunction (races between Earth and sun) Aug 19, 2025: Greatest elongation (morning) Sep 13, 2025: Superior conjunction (passes behind sun from Earth) Oct 29, 2025: Greatest elongation (evening) Nov 20, 2025: Inferior conjunction (races between Earth and sun) Dec 7, 2025: Greatest elongation (morning)
Mercury charts from Guy Ottewell
Mercury’s greatest morning elongations in 2025 from the Northern Hemisphere, as viewed through a powerful telescope. The planet images are at the 1st, 11th and 21st of each month. Here, dots show the actual positions of the planet for every day. Chart via Guy Ottewell’s 2025 Astronomical Calendar. Used with permission.Mercury’s greatest morning elongations in 2025 from the Southern Hemisphere, as viewed through a powerful telescope. The planet images are at the 1st, 11th and 21st of each month. Here, dots show the actual positions of the planet for every day. Chart via Guy Ottewell’s 2025 Astronomical Calendar. Used with permission.
A comparison of elongations
Mercury’s greatest elongations are not equal. Indeed, some are “greater” than others. For example, the distance of Mercury from the sun on our sky’s dome varies from about 28 degrees (maximum) to 18 degrees (minimum).
Also, Mercury elongations are better or worse depending on the time of the year they occur and your location on Earth. So, for both hemispheres, spring evenings and autumn mornings are best.
As an illustration, the chart below – from a Northern Hemisphere perspective – might help you visualize these differences.
Mercury elongations compared. Here, gray areas represent evening apparitions (eastward elongation). Blue areas represent morning apparitions (westward elongation). The top figures are the maximum elongations, reached at the top dates shown beneath. Curves show the altitude of the planet above the horizon at sunrise or sunset, for latitude 40 degrees north (thick line) and 35 degrees south (thin line). Likewise, maxima are reached at the parenthesized dates below (40 degrees north bold). Chart via Guy Ottewell’s 2025 Astronomical Calendar. Used with permission.
So, in the autumn for either hemisphere, the ecliptic – or path of the sun, moon and planets – makes a narrow angle to the horizon in the evening. Conversely, it makes a steep slant, nearly perpendicular, in the morning. So – in autumn from either hemisphere – morning elongations of Mercury are best. Then, Mercury appears higher above the horizon and farther from the glow of the sun. Conversely, evening elongations in autumn are harder to see.
On the other hand, in the spring for either hemisphere, the situation reverses. Then, the ecliptic and the horizon meet at a sharper angle on spring evenings and at a narrower angle on spring mornings. So, in springtime for either hemisphere, evening elongations of Mercury are best. Meanwhile, morning elongations in springtime are harder to see.
Bottom line: Mercury will reach its greatest elongation – greatest distance from the sunrise – on August 19, 2025. Look east at dawn. It’ll disappear from the morning sky later by month’s end. Also, the brilliant planet Venus and bright Jupiter are near Mercury in the morning sky.
At greatest elongation on August 19, 2025, Mercury will lie to one side of the sun as seen from Earth. That’s when it’s at its greatest distance from the sun before sunrise on our sky’s dome. Chart via EarthSky.
Mercury farthest from the sunrise on August 19
The innermost planet Mercury orbits the sun every 88 days. And Earth is moving, too. So Mercury goes between us and the sun pretty often, about every 116 days. It did this last at 0 UTC on August 1, 2025, reaching the point astronomers call inferior conjunction. And since then, Mercury has been speeding ahead of Earth in orbit. It re-emerged in our morning sky in early August. Mercury will reach its greatest morning elongation – its greatest apparent distance from the rising sun – on August 19, 2025. Also, brilliant Venus and Jupiter are near Mercury in the morning sky.
Mercury greatest elongation, August 2025
When to watch: Officially, Mercury emerged in early August in the morning sky. Look for it about 30 minutes before sunrise. At greatest elongation – August 19, 2025 – Mercury is farthest from the sunrise on our sky’s dome. And after that, when it’ll be edging back toward the sunrise, it’ll brighten a little bit more, making Mercury easier to spot – although low – in the morning twilight. Where to look: Look in the sunrise direction as the sky is getting lighter. Greatest elongation is on August 19 at 10 UTC (5:00 a.m. CDT). Mercury is shining at magnitude 0 that morning. And it’s 19 degrees from the sun. Through a telescope on and around August 19, Mercury appears 42% illuminated, in a crescent phase, and 7.33 arcseconds across. Note: Once you spot it, notice that Mercury brightens quickly as August progresses, reaching a magnitude of around -1.2 (bright, but competing with the morning twilight) late in August when it will slip away in the morning glare.
By the way, this Mercury elongation – due to the high angle of the ecliptic to the horizon – favors the Northern Hemisphere.
In the meantime, the innermost planet – named for the fleet-footed messenger god of the ancient Romans – will be visible for another week or two, especially from the Northern Hemisphere.
Finder charts for Mercury
In late August, for Northern Hemisphere viewers, brilliant Venus and bright Jupiter will lie near Mercury. Mercury will reach its greatest distance from the morning sun – or greatest western elongation – at 10 UTC on August 19. It will be 19 degrees from the sun then. And Mercury moves from the constellation of Cancer the Crab to Leo the Lion this month. Chart via EarthSky.In late August, for Southern Hemisphere viewers, brilliant Venus and bright Jupiter are near Mercury when it reaches its greatest distance from the sun on August 19. Mercury will lie low in the bright eastern twilight about 30 minutes before sunrise. Chart via EarthSky.
The moon visits Mercury
In the early morning hours on August 21, the thin waning crescent moon will lie below brilliant Venus and bright Jupiter and close to Mercury in the bright twilight. Nearby you’ll spot the bright star Procyon and Gemini’s twin stars, Castor and Pollux. Watch for them before dawn. Chart via EarthSky.
Mercury part of a planet parade
For those with optical aid, there will be 6 planets in the early morning sky the last few weeks of August. And you can see 4 of the planets with your eyes alone. Here’s the view from the Northern Hemisphere. You can catch Venus and Jupiter before dawn and through the brightening twilight. You might spot Mercury hiding in the morning twilight. Saturn is visible most of the night but will fade from view by dawn. To see Uranus and Neptune, you’ll need to use binoculars or a small telescope. Uranus lies between Venus and Saturn. And Neptune lies close to Saturn. The planets are all along the ecliptic, the path the sun travels in the daytime (the green line on our chart). Chart via EarthSky.
For precise sun and Mercury rising times at your location:
Feb 8, 2025: Superior conjunction (passes behind sun from Earth) Mar 8, 2025: Greatest elongation (evening) Mar 24, 2025: Inferior conjunction (races between Earth and sun) Apr 21, 2025: Greatest elongation (morning) May 30, 2025: Superior conjunction (passes behind sun from Earth) Jul 4, 2025: Greatest elongation (evening) Aug 1, 2025: Inferior conjunction (races between Earth and sun) Aug 19, 2025: Greatest elongation (morning) Sep 13, 2025: Superior conjunction (passes behind sun from Earth) Oct 29, 2025: Greatest elongation (evening) Nov 20, 2025: Inferior conjunction (races between Earth and sun) Dec 7, 2025: Greatest elongation (morning)
Mercury charts from Guy Ottewell
Mercury’s greatest morning elongations in 2025 from the Northern Hemisphere, as viewed through a powerful telescope. The planet images are at the 1st, 11th and 21st of each month. Here, dots show the actual positions of the planet for every day. Chart via Guy Ottewell’s 2025 Astronomical Calendar. Used with permission.Mercury’s greatest morning elongations in 2025 from the Southern Hemisphere, as viewed through a powerful telescope. The planet images are at the 1st, 11th and 21st of each month. Here, dots show the actual positions of the planet for every day. Chart via Guy Ottewell’s 2025 Astronomical Calendar. Used with permission.
A comparison of elongations
Mercury’s greatest elongations are not equal. Indeed, some are “greater” than others. For example, the distance of Mercury from the sun on our sky’s dome varies from about 28 degrees (maximum) to 18 degrees (minimum).
Also, Mercury elongations are better or worse depending on the time of the year they occur and your location on Earth. So, for both hemispheres, spring evenings and autumn mornings are best.
As an illustration, the chart below – from a Northern Hemisphere perspective – might help you visualize these differences.
Mercury elongations compared. Here, gray areas represent evening apparitions (eastward elongation). Blue areas represent morning apparitions (westward elongation). The top figures are the maximum elongations, reached at the top dates shown beneath. Curves show the altitude of the planet above the horizon at sunrise or sunset, for latitude 40 degrees north (thick line) and 35 degrees south (thin line). Likewise, maxima are reached at the parenthesized dates below (40 degrees north bold). Chart via Guy Ottewell’s 2025 Astronomical Calendar. Used with permission.
So, in the autumn for either hemisphere, the ecliptic – or path of the sun, moon and planets – makes a narrow angle to the horizon in the evening. Conversely, it makes a steep slant, nearly perpendicular, in the morning. So – in autumn from either hemisphere – morning elongations of Mercury are best. Then, Mercury appears higher above the horizon and farther from the glow of the sun. Conversely, evening elongations in autumn are harder to see.
On the other hand, in the spring for either hemisphere, the situation reverses. Then, the ecliptic and the horizon meet at a sharper angle on spring evenings and at a narrower angle on spring mornings. So, in springtime for either hemisphere, evening elongations of Mercury are best. Meanwhile, morning elongations in springtime are harder to see.
Bottom line: Mercury will reach its greatest elongation – greatest distance from the sunrise – on August 19, 2025. Look east at dawn. It’ll disappear from the morning sky later by month’s end. Also, the brilliant planet Venus and bright Jupiter are near Mercury in the morning sky.
White dwarf stars are the remaining cores of dead stars. After a dying star inflates into a red giant, it blows its gases into space, leaving behind the remaining core, or white dwarf.
A white dwarf 128 light-years away formed from the collision and merger of two stars, NASA’s Hubble Space Telescope has found. Most white dwarfs form from a single dying star.
The white dwarf is also more massive than the sun, which is rare. But it could mean that such stellar mergers are more common than previously thought.
A rare, massive white dwarf
A white dwarf star is the dense core that remains after a star has exhausted all of its fuel and blows its gases out into space. But now, astronomers have found a white dwarf that’s a little different. The researchers, led by the University of Warwick in the U.K., said on August 6, 2025, that this white dwarf, 128 light-years away, formed from two stars merging. They were possibly a white dwarf and a subgiant star. The Hubble Space Telescope discovered carbon in the white dwarf’s atmosphere, which provided clues to its origin. The white dwarf is also 1.2 times more massive than our sun, which is rare.
Hubble found the carbon when it observed the white dwarf in ultraviolet light. White dwarfs are common, but typically they’re about half the mass of the sun and the size of Earth. The findings could mean that massive white dwarfs resulting from stellar collisions are more common than previously thought.
The research team published the peer-reviewed details of their discovery in Nature Astronomy on August 6, 2025.
Carbon in white dwarf’s atmosphere hints at stellar collision
When Hubble observed the white dwarf – known as WD 0525+526 – it found small amounts of carbon in its atmosphere. This suggested that the white dwarf likely formed from the collision of two stars. And this could have been from the merger of a white dwarf and subgiant star.
Usually, carbon is concealed by hydrogen and helium around the core of the white dwarf.
But when two stars collide, that hydrogen and helium barrier can be stripped away. As a result, the carbon from deeper down can now reach the white dwarf’s atmosphere and be detected. As lead author Snehalata Sahu, Research Fellow at the University of Warwick, explained:
In optical light (the kind of light we see with our eyes), WD 0525+526 looks like a heavy but otherwise ordinary white dwarf. However, through ultraviolet observations obtained with Hubble, we were able to detect faint carbon signatures that were not visible to optical telescopes.
Finding small amounts of carbon in the atmosphere is a telltale sign that this massive white dwarf is likely to be the remnant of a merger between two stars colliding. It also tells us there may be many more merger remnants like this masquerading as common pure-hydrogen atmosphere white dwarfs. Only ultraviolet observations would be able to reveal them to us.
The researchers needed Hubble’s Cosmic Origins Spectrograph to be able to detect the carbon. Sahu said:
Hubble’s Cosmic Origins Spectrograph is the only instrument that can obtain the superb quality ultraviolet spectroscopy that was required to detect the carbon in the atmosphere of this white dwarf.
View larger. | Artist’s concept of a white dwarf star colliding and merging with a subgiant star. Image via NASA/ ESA/ STScI/ Ralf Crawford (STScI).
Much less carbon than usual
While there is carbon that was exposed during the merger, there is much less of it than typically seen in other stellar mergers. Co-author Antoine Bédard at Warwick said:
We measured the hydrogen and helium layers to be 10 billion times thinner than in typical white dwarfs. We think these layers were stripped away in the merger, and this is what now allows carbon to appear on the surface.
But this remnant is also unusual: it has about 100,000 times less carbon on its surface compared to other merger remnants. The low carbon level, together with the star’s high temperature (nearly four times hotter than the sun), tells us WD 0525+526 is much earlier in its post-merger evolution than those previously found. This discovery helps us build a better understanding of the fate of binary star systems, which is critical for related phenomena like supernova explosions.
Snehalata Sahu at the University of Warwick in the U.K. is the lead author of the new study about merging stars and white dwarfs. Image via Snehalata Sahu.
How does the carbon reach the surface of the white dwarf?
The researchers say it has to do with how old the carbon remnants are. Other star mergers that astronomers have previously found were already later in the merging process. This meant that temperatures had already cooled down significantly. They cooled enough for convection – the transfer of heat through a heated fluid – to bring carbon to the surface. That shouldn’t happen in star mergers that are younger and still too hot. But somehow, it does happen in WD 0525+526. This merger remnant white dwarf is still hot and the cooling process is “delayed,” as the paper describes it. So what is the explanation?
The researchers found a similar but subtler convection process occurring, called semi-convection. It allows small amounts of carbon to reach the surface in the white dwarf. This is the first time that astronomers have identified this process in a white dwarf.
Also, it could mean that this white dwarf is leftover from the merger of a white dwarf and subgiant star. As the paper notes:
This subpopulation of delayed white dwarfs is interpreted as being the descendants of certain types of stellar mergers, such as the merger of a white dwarf with a subgiant star.
Evidence of merger in massive white dwarf is unusual
It is rare to find evidence of star mergers in single white dwarfs. As co-author Boris Gänsicke at Warwick noted:
Finding clear evidence of mergers in individual white dwarfs is rare. But ultraviolet spectroscopy gives us the ability to detect these signs early, when the carbon is still invisible at optical wavelengths. Because the Earth’s atmosphere blocks ultraviolet light, these observations must be carried out from space, and currently only Hubble can do this job.
The researchers want to find out how common carbon-bearing white dwarfs actually are. Bédard said:
We would like to extend our research on this topic by exploring how common carbon white dwarfs are among similar white dwarfs, and how many stellar mergers are hiding among the normal white dwarf family. That will be an important contribution to our understanding of white dwarf binaries, and the pathways to supernova explosions.
Last April, astronomers at the University of Warwick also said they identified 2 nearbywhite dwarf stars that are on course to collide. The collision would create a supernova explosion in about 23 billion years. Image via University of Warwick/ Mark Garlick.
Things are not always as they 1st appear
The findings are also a reminder that things are not always as they might 1st appear. This is also true in space, of course. Gänsicke said:
It’s a discovery that underlines how things may be different from what they appear to us at first glance. Until now, this appeared as a normal white dwarf, but Hubble’s ultraviolet vision revealed that it had a very different history from what we would have guessed.
Bottom line: A rare massive white dwarf star 128 light-years away formed from the collision and merger of two stars, NASA’s Hubble Space Telescope has found.
White dwarf stars are the remaining cores of dead stars. After a dying star inflates into a red giant, it blows its gases into space, leaving behind the remaining core, or white dwarf.
A white dwarf 128 light-years away formed from the collision and merger of two stars, NASA’s Hubble Space Telescope has found. Most white dwarfs form from a single dying star.
The white dwarf is also more massive than the sun, which is rare. But it could mean that such stellar mergers are more common than previously thought.
A rare, massive white dwarf
A white dwarf star is the dense core that remains after a star has exhausted all of its fuel and blows its gases out into space. But now, astronomers have found a white dwarf that’s a little different. The researchers, led by the University of Warwick in the U.K., said on August 6, 2025, that this white dwarf, 128 light-years away, formed from two stars merging. They were possibly a white dwarf and a subgiant star. The Hubble Space Telescope discovered carbon in the white dwarf’s atmosphere, which provided clues to its origin. The white dwarf is also 1.2 times more massive than our sun, which is rare.
Hubble found the carbon when it observed the white dwarf in ultraviolet light. White dwarfs are common, but typically they’re about half the mass of the sun and the size of Earth. The findings could mean that massive white dwarfs resulting from stellar collisions are more common than previously thought.
The research team published the peer-reviewed details of their discovery in Nature Astronomy on August 6, 2025.
Carbon in white dwarf’s atmosphere hints at stellar collision
When Hubble observed the white dwarf – known as WD 0525+526 – it found small amounts of carbon in its atmosphere. This suggested that the white dwarf likely formed from the collision of two stars. And this could have been from the merger of a white dwarf and subgiant star.
Usually, carbon is concealed by hydrogen and helium around the core of the white dwarf.
But when two stars collide, that hydrogen and helium barrier can be stripped away. As a result, the carbon from deeper down can now reach the white dwarf’s atmosphere and be detected. As lead author Snehalata Sahu, Research Fellow at the University of Warwick, explained:
In optical light (the kind of light we see with our eyes), WD 0525+526 looks like a heavy but otherwise ordinary white dwarf. However, through ultraviolet observations obtained with Hubble, we were able to detect faint carbon signatures that were not visible to optical telescopes.
Finding small amounts of carbon in the atmosphere is a telltale sign that this massive white dwarf is likely to be the remnant of a merger between two stars colliding. It also tells us there may be many more merger remnants like this masquerading as common pure-hydrogen atmosphere white dwarfs. Only ultraviolet observations would be able to reveal them to us.
The researchers needed Hubble’s Cosmic Origins Spectrograph to be able to detect the carbon. Sahu said:
Hubble’s Cosmic Origins Spectrograph is the only instrument that can obtain the superb quality ultraviolet spectroscopy that was required to detect the carbon in the atmosphere of this white dwarf.
View larger. | Artist’s concept of a white dwarf star colliding and merging with a subgiant star. Image via NASA/ ESA/ STScI/ Ralf Crawford (STScI).
Much less carbon than usual
While there is carbon that was exposed during the merger, there is much less of it than typically seen in other stellar mergers. Co-author Antoine Bédard at Warwick said:
We measured the hydrogen and helium layers to be 10 billion times thinner than in typical white dwarfs. We think these layers were stripped away in the merger, and this is what now allows carbon to appear on the surface.
But this remnant is also unusual: it has about 100,000 times less carbon on its surface compared to other merger remnants. The low carbon level, together with the star’s high temperature (nearly four times hotter than the sun), tells us WD 0525+526 is much earlier in its post-merger evolution than those previously found. This discovery helps us build a better understanding of the fate of binary star systems, which is critical for related phenomena like supernova explosions.
Snehalata Sahu at the University of Warwick in the U.K. is the lead author of the new study about merging stars and white dwarfs. Image via Snehalata Sahu.
How does the carbon reach the surface of the white dwarf?
The researchers say it has to do with how old the carbon remnants are. Other star mergers that astronomers have previously found were already later in the merging process. This meant that temperatures had already cooled down significantly. They cooled enough for convection – the transfer of heat through a heated fluid – to bring carbon to the surface. That shouldn’t happen in star mergers that are younger and still too hot. But somehow, it does happen in WD 0525+526. This merger remnant white dwarf is still hot and the cooling process is “delayed,” as the paper describes it. So what is the explanation?
The researchers found a similar but subtler convection process occurring, called semi-convection. It allows small amounts of carbon to reach the surface in the white dwarf. This is the first time that astronomers have identified this process in a white dwarf.
Also, it could mean that this white dwarf is leftover from the merger of a white dwarf and subgiant star. As the paper notes:
This subpopulation of delayed white dwarfs is interpreted as being the descendants of certain types of stellar mergers, such as the merger of a white dwarf with a subgiant star.
Evidence of merger in massive white dwarf is unusual
It is rare to find evidence of star mergers in single white dwarfs. As co-author Boris Gänsicke at Warwick noted:
Finding clear evidence of mergers in individual white dwarfs is rare. But ultraviolet spectroscopy gives us the ability to detect these signs early, when the carbon is still invisible at optical wavelengths. Because the Earth’s atmosphere blocks ultraviolet light, these observations must be carried out from space, and currently only Hubble can do this job.
The researchers want to find out how common carbon-bearing white dwarfs actually are. Bédard said:
We would like to extend our research on this topic by exploring how common carbon white dwarfs are among similar white dwarfs, and how many stellar mergers are hiding among the normal white dwarf family. That will be an important contribution to our understanding of white dwarf binaries, and the pathways to supernova explosions.
Last April, astronomers at the University of Warwick also said they identified 2 nearbywhite dwarf stars that are on course to collide. The collision would create a supernova explosion in about 23 billion years. Image via University of Warwick/ Mark Garlick.
Things are not always as they 1st appear
The findings are also a reminder that things are not always as they might 1st appear. This is also true in space, of course. Gänsicke said:
It’s a discovery that underlines how things may be different from what they appear to us at first glance. Until now, this appeared as a normal white dwarf, but Hubble’s ultraviolet vision revealed that it had a very different history from what we would have guessed.
Bottom line: A rare massive white dwarf star 128 light-years away formed from the collision and merger of two stars, NASA’s Hubble Space Telescope has found.
View at EarthSky Community Photos. | Soumyadeep Mukherjee shared this composite image from photos he took at Singalila National Park in India. Soumyadeep wrote: “There are some images, which, after you create, make you happy. This is one of them. The image shows Venus in the varying backgrounds of twilight colors. As twilight progresses, the background stars, the Sagittarius arm and nebulae are slowly revealed. The change in colors and background within the same twilight period ranged around 26 minutes during this period and latitude.” Thank you, Soumyadeep!
Twilight is that magical time of day when a glow pervades the air, even though the sun is below the horizon. Earth’s atmosphere scatters the sun’s rays to create the colors of twilight. On worlds with no atmospheres, such as the moon, the sky falls instantly dark after the sun sets.
And, if you could see twilight from outer space, you’d find that it isn’t marked by a sharp boundary on Earth’s surface. Instead, the shadow line on Earth – sometimes called the terminator line – is spread over a fairly wide area on the surface and shows the gradual transition to darkness we all experience as night falls.
Astronomers – those experts on nighttime – recognize three stages of twilight. Keep reading or watch a video to hear about the intricacies of civil, nautical and astronomical twilight, below.
Stage 1: Civil twilight
Let’s consider the stages of twilight as occurring after sunset. Keep in mind that they would reverse their order at sunrise. Civil twilight begins the moment the sun slips below the horizon. The official definition of civil twilight is the time from when the sun disappears until the sun’s center is 6 degrees below the horizon. A measurement of 6 degrees of sky is a bit more than three fingers held at arm’s length.
During civil twilight, there’s enough light to see, but people turn on their lights to drive a car, and the streetlights are starting to come on. The brightest planets appear during civil twilight.
For mid latitudes, civil twilight lasts a bit longer in summer and winter and is a bit shorter in spring and fall. In spring and fall, the sun rises and sets more directly in the east and west. Therefore, it makes a straighter path downward (or upward), reaching the 6 degree mark in a shorter period of time. In summer and winter, the sun arcs across the sky, cutting across the horizon at an angle. This angle is more pronounced in summer, which is why civil twilight lasts the longest in summer. Civil twilight in mid latitudes can last, on average, 1/2 hour.
Compare this to tropical regions. At the equator, the length of civil twilight hardly varies. The sun around the equator makes a path across the sky that cuts cleanly down toward the horizon at sunset in a nearly perpendicular fashion. Therefore, the sun and its rays disappear faster, giving equatorial regions a shorter twilight than higher latitudes. Near the poles, twilight times last much longer.
In the evening, nautical twilight takes over where civil twilight ends. The definition of nautical twilight is the time period when the center of the sun is 6 degrees below the horizon to 12 degrees below the horizon. You can remember the name “nautical” because it ends when the distant line between sea and sky is no longer distinguishable. Also, more bright stars appear during this time, which was important in the early days of navigation. When nautical twilight began, sailors could use the stars as directional cues.
During nautical twilight, terrestrial objects are visible, but you need artificial lights to carry on outdoor activities.
For polar regions, the summer sun does not get more than 12 degrees below the horizon. Therefore, these regions have nautical twilight all night long, never reaching astronomical twilight or total darkness. For mid latitudes, nautical twilight can last from about 1/2 hour in spring, winter and fall, to about 45 minutes in summer.
Stage 3: Astronomical twilight
The darkest twilight stage is astronomical twilight. The definition of astronomical twilight is the period of time when the center of the sun is 12 degrees below the horizon to 18 degrees below the horizon. You probably don’t even notice any illumination left in the sky at this time.
For stargazers, this is the time when fainter stars, clusters and other sky objects appear and become good observing targets.
In mid latitudes, astronomical twilight can last about 1/2 hour from fall through spring but up to an hour in summer. Astronomical twilight begins about an hour to 1 1/2 hours after sunset for mid latitudes. So, as a rule of thumb, if you’d like to observe something in the night sky that isn’t particularly bright, you should wait about 90 minutes after sunset before you start observing.
Twilight photo gallery
Twilight on Earth, viewed from space. Astronauts aboard the International Space Station captured this photo – a single digital frame – in June 2001. On the right, you see Earth illuminated by the sun. On the left, it’s nighttime. Between, washed in subtle colors, is the realm of twilight. Image via ISS Expedition 2 Crew/ Gateway to Astronaut Photography of Earth/ NASA.View at EarthSky Community Photos. | John Ashley of Amado, Arizona, caputured this image on July 6, 2024, and wrote: “A 1% crescent moon sets through twilight haze beyond the large telescopes (left horizon) at Kitt Peak National Observatory (43 miles from the camera) just after sunset on Saturday, July 7, 2024.” Thank you, John!View at EarthSky Community Photos. | Pat Fogg in Claresholm, Alberta, Canada, captured this image of early twilight on June 23, 2023. Pat wrote: “Sunset looking west to the Porcupine Hills.” Thank you, Pat!
Bottom line: Twilight is that magical time between sunlight and darkness. Astronomers, the experts on nighttime, recognize three stages of twilight.
View at EarthSky Community Photos. | Soumyadeep Mukherjee shared this composite image from photos he took at Singalila National Park in India. Soumyadeep wrote: “There are some images, which, after you create, make you happy. This is one of them. The image shows Venus in the varying backgrounds of twilight colors. As twilight progresses, the background stars, the Sagittarius arm and nebulae are slowly revealed. The change in colors and background within the same twilight period ranged around 26 minutes during this period and latitude.” Thank you, Soumyadeep!
Twilight is that magical time of day when a glow pervades the air, even though the sun is below the horizon. Earth’s atmosphere scatters the sun’s rays to create the colors of twilight. On worlds with no atmospheres, such as the moon, the sky falls instantly dark after the sun sets.
And, if you could see twilight from outer space, you’d find that it isn’t marked by a sharp boundary on Earth’s surface. Instead, the shadow line on Earth – sometimes called the terminator line – is spread over a fairly wide area on the surface and shows the gradual transition to darkness we all experience as night falls.
Astronomers – those experts on nighttime – recognize three stages of twilight. Keep reading or watch a video to hear about the intricacies of civil, nautical and astronomical twilight, below.
Stage 1: Civil twilight
Let’s consider the stages of twilight as occurring after sunset. Keep in mind that they would reverse their order at sunrise. Civil twilight begins the moment the sun slips below the horizon. The official definition of civil twilight is the time from when the sun disappears until the sun’s center is 6 degrees below the horizon. A measurement of 6 degrees of sky is a bit more than three fingers held at arm’s length.
During civil twilight, there’s enough light to see, but people turn on their lights to drive a car, and the streetlights are starting to come on. The brightest planets appear during civil twilight.
For mid latitudes, civil twilight lasts a bit longer in summer and winter and is a bit shorter in spring and fall. In spring and fall, the sun rises and sets more directly in the east and west. Therefore, it makes a straighter path downward (or upward), reaching the 6 degree mark in a shorter period of time. In summer and winter, the sun arcs across the sky, cutting across the horizon at an angle. This angle is more pronounced in summer, which is why civil twilight lasts the longest in summer. Civil twilight in mid latitudes can last, on average, 1/2 hour.
Compare this to tropical regions. At the equator, the length of civil twilight hardly varies. The sun around the equator makes a path across the sky that cuts cleanly down toward the horizon at sunset in a nearly perpendicular fashion. Therefore, the sun and its rays disappear faster, giving equatorial regions a shorter twilight than higher latitudes. Near the poles, twilight times last much longer.
In the evening, nautical twilight takes over where civil twilight ends. The definition of nautical twilight is the time period when the center of the sun is 6 degrees below the horizon to 12 degrees below the horizon. You can remember the name “nautical” because it ends when the distant line between sea and sky is no longer distinguishable. Also, more bright stars appear during this time, which was important in the early days of navigation. When nautical twilight began, sailors could use the stars as directional cues.
During nautical twilight, terrestrial objects are visible, but you need artificial lights to carry on outdoor activities.
For polar regions, the summer sun does not get more than 12 degrees below the horizon. Therefore, these regions have nautical twilight all night long, never reaching astronomical twilight or total darkness. For mid latitudes, nautical twilight can last from about 1/2 hour in spring, winter and fall, to about 45 minutes in summer.
Stage 3: Astronomical twilight
The darkest twilight stage is astronomical twilight. The definition of astronomical twilight is the period of time when the center of the sun is 12 degrees below the horizon to 18 degrees below the horizon. You probably don’t even notice any illumination left in the sky at this time.
For stargazers, this is the time when fainter stars, clusters and other sky objects appear and become good observing targets.
In mid latitudes, astronomical twilight can last about 1/2 hour from fall through spring but up to an hour in summer. Astronomical twilight begins about an hour to 1 1/2 hours after sunset for mid latitudes. So, as a rule of thumb, if you’d like to observe something in the night sky that isn’t particularly bright, you should wait about 90 minutes after sunset before you start observing.
Twilight photo gallery
Twilight on Earth, viewed from space. Astronauts aboard the International Space Station captured this photo – a single digital frame – in June 2001. On the right, you see Earth illuminated by the sun. On the left, it’s nighttime. Between, washed in subtle colors, is the realm of twilight. Image via ISS Expedition 2 Crew/ Gateway to Astronaut Photography of Earth/ NASA.View at EarthSky Community Photos. | John Ashley of Amado, Arizona, caputured this image on July 6, 2024, and wrote: “A 1% crescent moon sets through twilight haze beyond the large telescopes (left horizon) at Kitt Peak National Observatory (43 miles from the camera) just after sunset on Saturday, July 7, 2024.” Thank you, John!View at EarthSky Community Photos. | Pat Fogg in Claresholm, Alberta, Canada, captured this image of early twilight on June 23, 2023. Pat wrote: “Sunset looking west to the Porcupine Hills.” Thank you, Pat!
Bottom line: Twilight is that magical time between sunlight and darkness. Astronomers, the experts on nighttime, recognize three stages of twilight.
