Astronomy Picture of the Day

🌌Striped Sand Dunes on Mars Why are these sand dunes on Mars striped? No one is sure. The featured image shows striped dunes in Kunowsky Crater on Mars, photographed recently with the Mars Reconnaissance Orbiter’s HiRISE Camera. Many Martian dunes are known to be covered unevenly with carbon dioxide (dry ice) frost, creating patterns of light and dark areas. Carbon dioxide doesn’t melt, but subl ...

© José Mtanous

🌌The Small Cloud of Magellan What is the Small Magellanic Cloud? It has turned out to be a galaxy. People who have wondered about this little fuzzy patch in the southern sky included Portuguese navigator Ferdinand Magellan and his crew, who had plenty of time to study the unfamiliar night sky of the south during the first circumnavigation of planet Earth in the early 1500s. As a result, two cele ...

🌌Sprite Lightning at 100,000 Frames Per Second What causes sprite lightning? Mysterious bursts of light in the sky that momentarily resemble gigantic jellyfish have been recorded for over 30 years, but apart from a general association with positive cloud-to-ground lightning, their root cause remains unknown. Some thunderstorms have them -- most don't. Recently, however, high speed videos are bet ...

© Hallgrimur P. Helgason Rollover Annotation: Judy Schmidt

🌌A Phoenix Aurora over Iceland All of the other aurora watchers had gone home. By 3:30 am in Iceland, on a quiet September night, much of that night's auroras had died down. Suddenly, unexpectedly, a new burst of particles streamed down from space, lighting up the Earth's atmosphere once again. This time, surprisingly, pareidoliacally, the night lit up with an amazing shape reminiscent of a gian ...

© wet-plate collodion

🌌21st Century Wet Collodion Moon In the mid 19th century, one of the first photographic technologies used to record the lunar surface was the wet-plate collodion process, notably employed by British astronomer Warren De la Rue. To capture an image, a thick, transparent mixture was used to coat a glass plate, sensitized with silver nitrate, exposed at the telescope, and then developed to create a ...

© Petr Horalek

🌌Galaxies and the South Celestial Pole The South Celestial Pole is easy to spot in star trail images of the southern sky. The extension of Earth's axis of rotation to the south, it's at the center of all the southern star trail arcs. In this starry panorama streching about 60 degrees across deep southern skies the South Celestial Pole is somewhere near the middle though, flanked by bright galaxi ...

© Zhuoxiao Wang

🌌Trail of the Returner Familiar stars of a northern winter's night shine in this night skyview, taken near Zhangye, Gansu, China and the border with Inner Mongolia. During the early hours of December 17 Orion is near center in the single exposure that captures a fireball streaking across the sky, almost as bright as yellowish Mars shining on the right. Splitting Gemini's twin bright stars Castor ...

🌌Jupiter and Saturn Great Conjunction: The Movie Yes, but have you seen a movie of Jupiter and Saturn's Great Conjunction? The featured time-lapse video was composed from a series of images taken from Thailand and shows the two giant planets as they angularly passed about a tenth of a degree from each other. The first Great Conjunction sequence shows a relative close up over five days with moons ...

🌌Earth During a Total Solar Eclipse What does the Earth look like during a total solar eclipse? It appears dark in the region where people see the eclipse, because that's where the shadow of the Moon falls. The shadow spot rapidly shoots across the Earth at nearly 2,000 kilometers per hour, darkening locations in its path -- typically for only a few minutes -- before moving on. The featured vide ...

© Nicolas Paladini

🌌M16: Inside the Eagle Nebula From afar, the whole thing looks like an Eagle. A closer look at the Eagle Nebula, however, shows the bright region is actually a window into the center of a larger dark shell of dust. Through this window, a brightly-lit workshop appears where a whole open cluster of stars is being formed. In this cavity tall pillars and round globules of dark dust and cold molecula ...

🌌Cosmic Latte: The Average Color of the Universe What color is the universe? More precisely, if the entire sky were smeared out, what color would the final mix be? This whimsical question came up when trying to determine what stars are commonplace in nearby galaxies. The answer, depicted above, is a conditionally perceived shade of beige. In computer parlance: #FFF8E7. To determine this, astrono ...

© Miguel Claro

🌌Fox Fur, Unicorn, and Christmas Tree Clouds of glowing hydrogen gas fill this colorful skyscape in the faint but fanciful constellation Monoceros, the Unicorn. A star forming region cataloged as NGC 2264, the complex jumble of cosmic gas and dust is about 2,700 light-years distant and mixes reddish emission nebulae excited by energetic light from newborn stars with dark interstellar dust clouds ...

© Adam Block

🌌Northern Winter Night Orion always seems to come up sideways on northern winter evenings. Those familiar stars of the constellation of the Hunter are caught above the trees in this colorful night skyscape. Not a star at all but still visible to eye, the Great Nebula of Orion shines below the Hunter's belt stars. The camera's exposure reveals the stellar nursery's faint pinkish glow. Betelgeuse, ...

© Martin Pugh

🌌Portrait of NGC 1055 Big, beautiful spiral galaxy NGC 1055 is a dominant member of a small galaxy group a mere 60 million light-years away toward the aquatically intimidating constellation Cetus. Seen edge-on, the island universe spans over 100,000 light-years, a little larger than our own Milky Way galaxy. The colorful, spiky stars decorating this cosmic portrait of NGC 1055 are in the foregro ...

© Damian Peach

🌌Jupiter Meets Saturn: A Red Spotted Great Conjunction It was time for their close-up. Two days ago Jupiter and Saturn passed a tenth of a degree from each other in what is known a Great Conjunction. Although the two planets pass each other on the sky every 20 years, this was the closest pass in nearly four centuries. Taken early in day of the Great Conjunction, the featured multiple-exposure co ...

🌌Trifid Pillars and Jets Dust pillars are like interstellar mountains. They survive because they are more dense than their surroundings, but they are being slowly eroded away by a hostile environment. Visible in the featured picture is the end of a huge gas and dust pillar in the Trifid Nebula (M20), punctuated by a smaller pillar pointing up and an unusual jet pointing to the left. Many of the ...

© Zaid M. Al-Abbadi

🌌Solstice: Sunrises Around the Year Does the Sun always rise in the same direction? No. As the months change, the direction toward the rising Sun changes, too. The featured image shows the direction of sunrise every month during 2019 as seen from near the city of Amman, Jordan. The camera in the image is always facing due east, with north toward the left and south toward the right. Although the ...

© Francisco Sojuel

🌌A Volcanic Great Conjunction Where can I see the Great Conjunction? Near where the Sun just set. Directionally, this close passing of Jupiter and Saturn will be toward the southwest. Since the planetary pair, the Sun, and the Earth are nearly in a geometric straight line, the planets will be seen to set just where the Sun had set -- from every location on Earth. When can I see the Great Conjunc ...

© Alireza Vafa

🌌Conjunction after Sunset How close will Jupiter and Saturn be at their Great Conjunction? Consider this beautiful triple conjunction of Moon, Jupiter and Saturn captured through clouds in the wintry twilight. The telephoto view looks toward the western horizon and the Alborz Mountains in Iran after sunset on December 17. The celestial gathering makes it easy to see Jupiter and fainter Saturn ar ...

© Mariano Ribas

🌌Diamond in the Sky When the shadow of the Moon raced across planet Earth's southern hemisphere on December 14, sky watchers along the shadow's dark central path were treated to the only total solar eclipse of 2020. During the New Moon's shadow play this glistening diamond ring was seen for a moment, even in cloudy skies. Known as the diamond ring effect, the transient spectacle actually happens ...

© Stefano Pellegrini

🌌Gemini's Meteors Taken over the course of an hour shortly after local midnight on December 13, 35 exposures were used to create this postcard from Earth. The composited night scene spans dark skies above the snowy Italian Dolomites during our fair planet's annual Geminid meteor shower. Sirius, alpha star of Canis Major and the brightest star in the night, is grazed by a meteor streak on the rig ...

🌌Sonified: The Matter of the Bullet Cluster What's the matter with the Bullet Cluster? This massive cluster of galaxies (1E 0657-558) creates gravitational lens distortions of background galaxies in a way that has been interpreted as strong evidence for the leading theory: that dark matter exists within. Different analyses, though, indicate that a less popular alternative -- modifying gravity-- ...

© Sebastian Voltmer

🌌Great Conjunction: Saturn and Jupiter Converge It's happening. Saturn and Jupiter are moving closer and will soon appear in almost exactly the same direction. Coincidentally, on the night of the December solstice -- the longest night of the year in the north and the longest day in the south -- the long-awaited Great Conjunction will occur. Then, about six days from now, Saturn and Jupiter will ...

🌌Capsule Returns from Asteroid Ryugu The streak across the sky is a capsule returning from an asteroid. It returned earlier this month from the near-Earth asteroid 162173 Ryugu carrying small rocks and dust from its surface. The canister was released by its mothership, Japan's Hayabusa2, a mission that visited Ryugu in 2018, harvested a surface sample in 2019, and zoomed back past Earth. The jet ...

© Steed YuNightChina.net

🌌Geminid Meteors over Xinglong Observatory Where do Geminid meteors come from? In terms of location on the sky, as the featured image composite beautifully demonstrates, the sand-sized bits of rock that create the streaks of the Geminids meteor shower appear to flow out from the constellation of Gemini. In terms of parent body, Solar System trajectories point to the asteroid 3200 Phaethon -- but ...

© Tunc Tezel

🌌Saturn and Jupiter in Summer 2020 During this northern summer Saturn and Jupiter were both near opposition, opposite the Sun in planet Earth's sky. Their paired retrograde motion, seen about every 20 years, is followed from 19 June through 28 August in this panoramic composite as they wander together between the stars in western Capricornus and eastern Sagittarius. But this December's skies fin ...

🌌Messier Craters in Stereo Many bright nebulae and star clusters in planet Earth's sky are associated with the name of astronomer Charles Messier from his famous 18th century catalog. His name is also given to these two large and remarkable craters on the Moon. Standouts in the dark, smooth lunar Sea of Fertility or Mare Fecunditatis, Messier (left) and Messier A have dimensions of 15 by 8 and 1 ...

© Georges Attard