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NASA Astronomy Picture of the Day:

Why would the sky glow like a giant repeating rainbow? Airglow. Now, air glows all of the time, but it is usually hard to see. A disturbance however -- like an approaching storm -- may cause noticeable rippling in the Earth's atmosphere. These gravity waves are oscillations in air analogous to those created when a rock is thrown in calm water. The long-duration exposure nearly along the vertical walls of airglow likely made the undulating structure particularly visible. OK, but where do the colors originate? The deep red glow likely originates from OH molecules about 87 kilometers high, excited by ultraviolet light from the Sun. The orange and green airglow is likely caused by sodium and oxygen atoms slightly higher up. The featured image was captured during a climb up Mount Pico in the Azores of Portugal. Ground lights originate from the island of Faial in the Atlantic Ocean. A spectacular sky is visible through this banded airglow, with the central band of our Milky Way Galaxy running up the image center, and M31, the Andromeda Galaxy, visible near the top left. APOD Turns 30!: Free Public Lecture in Anchorage on June 11

Photo by Miguel Claro (TWAN); Rollover Annotation: Judy Schmidt

NASA Astronomy Picture of the Day:

Wisps like this are all that remain visible of a Milky Way star. About 7,000 years ago that star exploded in a supernova, leaving the Veil Nebula. At the time, the expanding cloud was likely as bright as a crescent Moon, remaining visible for weeks to people living at the dawn of recorded history. Today, the resulting supernova remnant, also known as the Cygnus Loop, has faded and is now visible only through a small telescope directed toward the constellation of the Swan (Cygnus). The remaining Veil Nebula is physically huge, however, and even though it lies about 1,400 light-years distant, it covers over five times the size of the full Moon. The featured picture was taken in Kuwait in mid-2024 and features light emitted by hydrogen in red and oxygen in blue. In deep images of the complete Veil Nebula like this, even studious readers might not be able to identify the iconic filaments. Piece it All Together: Astronomy Puzzle of the Day

Photo by Abdullah Alharbi

NASA Astronomy Picture of the Day:

What's happening to this spiral galaxy? Although details remain uncertain, it surely has to do with an ongoing battle with its smaller galactic neighbor. The featured galaxy is labelled UGC 1810 by itself, but together with its collisional partner is known as Arp 273. The overall shape of UGC 1810 -- in particular its blue outer ring -- is likely a result of wild and violent gravitational interactions. This ring's blue color is caused by massive stars that are blue hot and have formed only in the past few million years. The inner galaxy appears older, redder, and threaded with cool filamentary dust. A few bright stars appear well in the foreground, unrelated to UGC 1810, while several galaxies are visible well in the background. Arp 273 lies about 300 million light years away toward the constellation of Andromeda. Quite likely, UGC 1810 will devour its galactic sidekick over the next billion years and settle into a classic spiral form.

Photo by Domingo Pestana

NASA Astronomy Picture of the Day:

On May 7, the Sun setting behind a church bell tower was captured in this filtered and manipulated digital skyscape from Ragusa, Sicily, planet Earth. In this version of the image the colors look bizarre. Still, an intriguing optical illusion known as an afterimage can help you experience the same scene with a more natural looking appearance. To try it, find the sunspots of active region AR4079 grouped near the bottom of the blue solar disk. Relax and stare at the dark sunspot group for about 30 seconds, then close your eyes or shift your gaze to a plain white surface. In a moment an afterimage of the sunset should faintly appear. But the afterimage sunset will have this image's complementary colors and a more normal yellow Sun against a familiar blue sky.

Photo by Marcella Giulia Pace

NASA Astronomy Picture of the Day:

This composite of images spaced a weather-permitting 5 to 9 days apart, from 2024 September 19 (top right) through 2025 May 18 (bottom left), faithfully traces ruddy-colored Mars as it makes a clockwise loop through the constellations Gemini and Cancer in planet Earth's night sky. You can connect the dots and dates with your cursor over the image, but be sure to check out this animation of the Red Planet's 2024/25 retrograde motion. Of course Mars didn't actually reverse the direction of its orbit. Instead, the apparent backwards motion with respect to the background stars is a reflection of the orbital motion of Earth itself. Retrograde motion can be seen each time Earth overtakes and laps planets orbiting farther from the Sun, the Earth moving more rapidly through its own relatively close-in orbit. In this case Mars' apparent eastward motion began to reverse around December 8, when it seemed to linger near open star cluster M44 in Cancer. After wandering back to the west, under Gemini's bright stars Castor and Pollux, Mars returned to pose near M44 by early May. At its brightest near opposition on 2025 January 16, Mars was a mere 96 million kilometers away.

Photo by Tunc Tezel

NASA Astronomy Picture of the Day:

Grand spiral galaxies often seem to get all the attention, flaunting young, bright, blue star clusters and pinkish star forming regions along graceful, symmetric spiral arms. But small galaxies form stars too, like irregular dwarf galaxy Sextans A. Its young star clusters and star forming regions are gathered into a gumdrop-shaped region a mere 5,000 light-years across. Seen toward the navigational constellation Sextans, the small galaxy lies some 4.5 million light-years distant. That puts it near the outskirts of the local group of galaxies, that includes the large, massive spirals Andromeda and our own Milky Way. Brighter Milky Way foreground stars appear spiky and yellowish in this colorful telescopic view of Sextans A.

Photo by Franz Hofmann

NASA Astronomy Picture of the Day:

This might look like a double-bladed lightsaber, but these two cosmic jets actually beam outward from a newborn star in a galaxy near you. Constructed from Hubble Space Telescope image data, the stunning scene spans about half a light-year across Herbig-Haro 24 (HH 24), some 1,300 light-years or 400 parsecs away in the stellar nurseries of the Orion B molecular cloud complex. Hidden from direct view, HH 24's central protostar is surrounded by cold dust and gas flattened into a rotating accretion disk. As material from the disk falls toward the young stellar object, it heats up. Opposing jets are blasted out along the system's rotation axis. Cutting through the region's interstellar matter, the narrow, energetic jets produce a series of glowing shock fronts along their path.

NASA Astronomy Picture of the Day:

Behold one of the most photogenic regions of the night sky, captured impressively. Featured, the band of our Milky Way Galaxy runs diagonally along the bottom-left corner, while the colorful Rho Ophiuchi cloud complex is visible just right of center and the large red circular Zeta Ophiuchi Nebula appears near the top. In general, red emanates from nebulas glowing in the light of excited hydrogen gas, while blue marks interstellar dust preferentially reflecting the light of bright young stars. Thick dust usually appears dark brown. Many iconic objects of the night sky appear, including (can you find them?) the bright star Antares, the globular star cluster M4, and the Blue Horsehead nebula. This wide field composite, taken over 17 hours, was captured from South Africa last June. Explore Your Universe: Random APOD Generator

Photo by Ireneusz Nowak

NASA Astronomy Picture of the Day:

What’s happening in the center of spiral galaxy NGC 2566? First, the eight rays that appear to be coming out of the center in the featured infrared image are not real — they are diffraction spikes caused by the mechanical structure of the Webb space telescope itself. The center of NGC 2566 is bright but not considered unusual, which means that it likely contains a supermassive black hole, although currently not very active. At only 76 million light years away, the light we see from NGC 2566 today left when dinosaurs roamed the Earth. The picturesque galaxy is close enough so that Earthly telescopes, including Webb and Hubble, can resolve the turbulent clouds of gas and dust where stars can form and so allows study of stellar evolution. NGC 2566, similar in size to our Milky Way Galaxy, is notable for its bright central bar and its prominent outer spiral arms.

NASA Astronomy Picture of the Day:

Jupiter is stranger than we knew. NASA's Juno spacecraft has now completed over 70 swoops past Jupiter as it moves around its highly elliptical orbit. Pictured from 2017, Jupiter is seen from below where, surprisingly, the horizontal bands that cover most of the planet disappear into swirls and complex patterns. A line of white oval clouds is visible nearer to the equator. Impressive results from Juno show that Jupiter's weather phenomena can extend deep below its cloud tops, that Jupiter's center has a core that is unexpectedly large and soft, and that Jupiter's magnetic field varies greatly with location. Although Juno is scheduled to keep orbiting Jupiter further into 2025, at some time the robotic spacecraft will be maneuvered to plunge into the giant planet. Jigsaw Jumble: Astronomy Puzzle of the Day

Photo by NASA, Juno, SwRI, MSSS; Processing & License: Gerald Eichstädt & Seán Doran

NASA Astronomy Picture of the Day:

Deimos takes 30 hours and 18 minutes to complete one orbit around the Red Planet. That's a little more than one Martian day or sol which is about 24 hours and 40 minutes long, so Deimos drifts westward across the Martian sky. About 15 kilometers across at its widest, the smallest of Mars' two moons is bright though. In fact Deimos is the brightest celestial object in this Martian skyscape captured before sunrise by Perseverance on March 1, the 1,433rd sol of the Mars rover's mission. The image is a composed of 16 exposures recorded by one of the rover's navigation cameras. The individual exposures were combined into a single image for an enhanced low light view. Regulus and Algeiba, bright stars in the constellation Leo, are also visible in the dark Martian predawn sky.

NASA Astronomy Picture of the Day:

Most globular star clusters roam the halo of our Milky Way galaxy, but globular cluster NGC 6366 lies close to the galactic plane. About 12,000 light-years away toward the constellation Ophiuchus, the cluster's starlight is dimmed and reddened by the Milky Way's interstellar dust when viewed from planet Earth. As a result, the stars of NGC 6366 look almost golden in this telescopic scene, especially when seen next to relatively bright, bluish, and nearby star 47 Ophiuchi. Compared to the hundred thousand stars or so gravitationally bound in distant NGC 6366, 47 Oph itself is a binary star system a mere 100 light-years away. Still, the co-orbiting stars of 47 Oph are too close together to be individually distinguished in the image.

Photo by Massimo Di Fusco