NASA Astronomy Picture of the Day:

The night side of Pluto spans this shadowy scene. In the stunning spacebased perspective the Sun is 4.9 billion kilometers (almost 4.5 light-hours) behind the dim and distant world. It was captured by far flung New Horizons in July of 2015 when the spacecraft was at a range of some 21,000 kilometers from Pluto, about 19 minutes after its closest approach. A denizen of the Kuiper Belt in dramatic silhouette, the image also reveals Pluto's tenuous, surprisingly complex layers of hazy atmosphere. Near the top of the frame the crescent twilight landscape includes southern areas of nitrogen ice plains now formally known as Sputnik Planitia and rugged mountains of water-ice in the Norgay Montes.

NASA Astronomy Picture of the Day:

Braided and serpentine filaments of glowing gas suggest this nebula's popular name, The Medusa Nebula. Also known as Abell 21, this Medusa is an old planetary nebula some 1,500 light-years away in the constellation Gemini. Like its mythological namesake, the nebula is associated with a dramatic transformation. The planetary nebula phase represents a final stage in the evolution of low mass stars like the sun as they transform themselves from red giants to hot white dwarf stars and in the process shrug off their outer layers. Ultraviolet radiation from the hot star powers the nebular glow. The Medusa's transforming star is the faint one near the center of the overall bright crescent shape. In this deep telescopic view, fainter filaments clearly extend above and left of the bright crescent region. The Medusa Nebula is estimated to be over 4 light-years across.

Photo by Damien Cannane

NASA Astronomy Picture of the Day:

Peculiar spiral galaxy Arp 78 is found within the boundaries of the head strong constellation Aries. Some 100 million light-years beyond the stars and nebulae of our Milky Way galaxy, the island universe is over 100,000 light-years across. Also known as NGC 772, it sports a prominent, outer spiral arm in this detailed cosmic portrait from the large Gemini North telescope near the summit of Maunakea, Hawaii, planet Earth. Tracking along sweeping dust lanes and lined with young blue star clusters, Arp 78's spiral arm is likely pumped-up by galactic-scale gravitational tidal interactions The close companion galaxy responsible is NGC 770, located off the upper right of this frame. But more distant background galaxies are clearly visible in the cosmic field of view.

NASA Astronomy Picture of the Day:

Massive stars can blow bubbles. The featured image shows perhaps the most famous of all star-bubbles, NGC 7635, also known simply as The Bubble Nebula. Although it looks delicate, the 7-light-year diameter bubble offers evidence of violent processes at work. Above and left of the Bubble's center is a hot, O-type star, several hundred thousand times more luminous and some 45-times more massive than the Sun. A fierce stellar wind and intense radiation from that star has blasted out the structure of glowing gas against denser material in a surrounding molecular cloud. The intriguing Bubble Nebula and associated cloud complex lie a mere 7,100 light-years away toward the boastful constellation Cassiopeia. This sharp, tantalizing view of the cosmic bubble is a reprocessed composite of previously acquired Hubble Space Telescope image data. Birthday Surprise: What picture did APOD feature on your birthday? (post 1995)

NASA Astronomy Picture of the Day:

What's that in the sky? An aurora. A large coronal mass ejection occurred on our Sun earlier this month, throwing a cloud of fast-moving electrons, protons, and ions toward the Earth. Part of this cloud impacted our Earth's magnetosphere and, bolstered by a sudden gap, resulted in spectacular auroras being seen at some high northern latitudes. Featured here is a particularly photogenic auroral corona captured above a forest in Sweden from a scenic perch overlooking the city of Östersund. To some, this shimmering green glow of recombining atmospheric oxygen might appear like a large whale, but feel free to share what it looks like to you. The unusually quiet Sun of the past few years has now passed. As our Sun now approaches a solar maximum in its 11-year solar magnetic cycle, dramatic auroras like this are sure to continue. Open Science: Browse 2,700+ codes in the Astrophysics Source Code Library

Photo by Göran Strand

NASA Astronomy Picture of the Day:

What if you could see the entire sky -- all at once -- for an entire year? That, very nearly, is what is pictured here. Every 15 minutes during 2021, an all-sky camera took an image of the sky over the Netherlands. Central columns from these images were then aligned and combined to create the featured keogram, with January at the top, December at the bottom, and the middle of the night running vertically just left of center. What do we see? Most obviously, the daytime sky is mostly blue, while the nighttime sky is mostly black. The twelve light bands crossing the night sky are caused by the glow of the Moon. The thinnest part of the black hourglass shape occurs during the summer solstice when days are the longest, while the thickest part occurs at the winter solstice. Yesterday was an equinox -- when night and day were equal -- and the northern-spring equinox from one year ago can actually be located in the keogram -- about three-quarters of the way up. Follow APOD on Instagram in: English, Indonesian, Persian, Portuguese or Taiwanese

Photo by Cees BassaNetherlands Institute for Radio Astronomy

NASA Astronomy Picture of the Day:

What's that at the end of the road? The Sun. Many towns have roads that run east - west, and on two days each year, the Sun rises and sets right down the middle. Today is one of those days: an equinox. Not only is today a day of equal night ("aequus"-"nox") and day time, but also a day when the sun rises precisely to the east and sets due west. Featured here is a picturesque road in northwest Illinois, USA that runs approximately east -west. The image was taken during the March Equinox of 2015, and shows the Sun down the road at sunset. In many cultures, this March equinox is taken to be the first day of a season, typically spring in Earth's northern hemisphere, and autumn in the south. Does your favorite street run east - west? Tonight, at sunset, you can find out with a quick glance.

Photo by Roland Christen

NASA Astronomy Picture of the Day:

2MASS J17554042+6551277 doesn't exactly roll off the tongue but that's the name, a coordinate-based catalog designation, of the star centered in this sharp field of view. Fans of the distant universe should get used to its spiky appearance though. The diffraction pattern is created by the 18 hexagonal mirror segments of the James Webb Space Telescope. After unfolding, the segments have now been adjusted to achieve a diffraction limited alignment at infrared wavelengths while operating in concert as a single 6.5 meter diameter primary mirror. The resulting image taken by Webb's NIRcam demonstrates their precise alignment is the best physics will allow. 2MASS J17554042+6551277 is about 2,000 light-years away and well within our own galaxy. But the galaxies scattered across the background of the Webb telescope alignment evaluation image are likely billions of light-years distant, far beyond the Milky Way.

NASA Astronomy Picture of the Day:

Bluish reflection nebulae seem to fill this dusty expanse. The sharp telescopic frame spans over 1 degree on the sky toward the faint but fanciful constellation Monoceros, the Unicorn. Seen within the Monoceros R1 cloud complex some 2,500 light-years away, bluish IC 447 is on the left, joined by a long dark filament of dust to IC 446 at lower right. Embedded in IC 447 are young, massive blue stars much hotter than the Sun, whose light is reflected by the cosmic cloud of star stuff. Observations reveal that IC 446 also contains a young stellar object, a massive star still in an early stage of evolution. The dark filament of dust and molecular gas joining the two star-forming regions is over 15 light-years long.

Photo by Giorgio Ferrari

NASA Astronomy Picture of the Day:

A mere 11 million light-years away, Centaurus A is the closest active galaxy to planet Earth. Spanning over 60,000 light-years, the peculiar elliptical galaxy also known as NGC 5128, is featured in this sharp telescopic view. Centaurus A is apparently the result of a collision of two otherwise normal galaxies resulting in a fantastic jumble of star clusters and imposing dark dust lanes. Near the galaxy's center, leftover cosmic debris is steadily being consumed by a central black hole with a billion times the mass of the Sun. As in other active galaxies, that process likely generates the enormous radio, X-ray, and gamma-ray energy radiated by Centaurus A.

Photo by David Alemazkour

NASA Astronomy Picture of the Day:

How far can you see? Everything you can see, and everything you could possibly see, right now, assuming your eyes could detect all types of radiations around you -- is the observable universe. In light, the farthest we can see comes from the cosmic microwave background, a time 13.8 billion years ago when the universe was opaque like thick fog. Some neutrinos and gravitational waves that surround us come from even farther out, but humanity does not yet have the technology to detect them. The featured image illustrates the observable universe on an increasingly compact scale, with the Earth and Sun at the center surrounded by our Solar System, nearby stars, nearby galaxies, distant galaxies, filaments of early matter, and the cosmic microwave background. Cosmologists typically assume that our observable universe is just the nearby part of a greater entity known as "the universe" where the same physics applies. However, there are several lines of popular but speculative reasoning that assert that even our universe is part of a greater multiverse where either different physical constants occur, different physical laws apply, higher dimensions operate, or slightly different-by-chance versions of our standard universe exist. Available: High res image version with readable annotations | Clickable annotation version

NASA Astronomy Picture of the Day:

Pictured -- a very scenic road to the stars. The road approaches La Silla Observatory in Chile, with the ESO's 3.6-meter telescope just up ahead. To the left are some futuristic-looking support structures for the planned BlackGEM telescopes, an array of optical telescopes that will help locate optical counterparts to gravitational waves detections by LIGO and other detectors. But there is much more. Red airglow illuminates the night sky on the right, while the central band of our Milky Way Galaxy slants across the image center. Jupiter can be seen just above the band near the image center, while Saturn is visible just above the 3.6-meter telescope dome. The two largest satellite galaxies of our Milky Way Galaxy, the LMC and SMC, are seen on the far right. The featured image panorama was built up from multiple 15-second exposures that were captured on 2019 June 30. Two days later, La Silla experienced a rare total eclipse of the Sun.