NASA's Astronomy Picture of the Day
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Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
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2023 May 26

Virgo Cluster Galaxies
Image Credit &
Copyright: Abdullah Alharbi

Galaxies of the Virgo Cluster are scattered across this nearly 4 degree wide telescopic field of view. About 50 million light-years distant, the Virgo Cluster is the closest large galaxy cluster to our own local galaxy group. Prominent here are Virgo's bright elliptical galaxies Messier catalog, M87 at bottom center, and M84 and M86 (top to bottom) near top left. M84 and M86 are recognized as part of Markarian's Chain, a visually striking line-up of galaxies on the left side of this frame. Near the middle of the chain lies an intriguing interacting pair of galaxies, NGC 4438 and NGC 4435, known to some as Markarian's Eyes. Of course giant elliptical galaxy M87 dominates the Virgo cluster. It's the home of a super massive black hole, the first black hole ever imaged by planet Earth's Event Horizon Telescope.
2023 May 27

Crescent Neptune and Triton
Image Credit:
NASA, Voyager 2

Gliding through the outer Solar System, in 1989 the Voyager 2 spacecraft looked toward the Sun to find this view of most distant planet Neptune and its moon Triton together in a crescent phase. The elegant image of ice-giant planet and largest moon was taken from behind just after Voyager's closest approach. It could not have been taken from Earth because the most distant planet never shows a crescent phase to sunward eyes. Heading for the heliopause and beyond, the spacecraft's parting vantage point also robs Neptune of its familiar blue hue.
2023 May 28

Ida and Dactyl: Asteroid and Moon
Image Credit:
NASA, JPL, Galileo Mission

This asteroid has a moon. The robot spacecraft Galileo on route to Jupiter in 1993 encountered and photographed two asteroids during its long interplanetary voyage. The second minor planet it photographed, 243 Ida, was unexpectedly discovered to have a moon. The tiny moon, Dactyl, is only about 1.6 kilometers across and seen as a small dot on the right of the sharpened featured image. In contrast, the potato-shaped Ida is much larger, measuring about 60 kilometers long and 25 km wide. Dactyl is the first moon of an asteroid ever discovered -- now many asteroids are known to have moons. The names Ida and Dactyl are from Greek mythology.
2023 May 29

Milky Way over a Turquoise Wonderland
Image Credit & Copyright:
Petr Horálek / Institute of Physics in Opava, Sovena Jani

What glows there? The answer depends: sea or sky? In the sea, the unusual blue glow is bioluminescence. Specifically, the glimmer arises from Noctiluca scintillans, single-celled plankton stimulated by the lapping waves. The plankton use their glow to startle and illuminate predators. This mid-February display on an island in the Maldives was so intense that the astrophotographer described it as a turquoise wonderland. In the sky, by contrast, are the more familiar glows of stars and nebulas. The white band rising from the artificially-illuminated green plants is created by billions of stars in the central disk of our Milky Way Galaxy. Also visible in the sky is the star cluster Omega Centauri, toward the left, and the famous Southern Cross asterism in the center. Red-glowing nebulas include the bright Carina Nebula, just right of center, and the expansive Gum Nebula on the upper right.
2023 May 30

M27: The Dumbbell Nebula
Image Credit & Copyright:
Patrick A. Cosgrove

Is this what will become of our Sun? Quite possibly. The first hint of our Sun's future was discovered inadvertently in 1764. At that time, Charles Messier was compiling a list of diffuse objects not to be confused with comets. The 27th object on Messier's list, now known as M27 or the Dumbbell Nebula, is a planetary nebula, one of the brightest planetary nebulae on the sky and visible with binoculars toward the constellation of the Fox (Vulpecula). It takes light about 1000 years to reach us from M27, featured here in colors emitted by sulfur (red), hydrogen (green) and oxygen (blue). We now know that in about 6 billion years, our Sun will shed its outer gases into a planetary nebula like M27, while its remaining center will become an X-ray hot white dwarf star. Understanding the physics and significance of M27 was well beyond 18th century science, though. Even today, many things remain mysterious about planetary nebulas, including how their intricate shapes are created.
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2023 May 31

Simulation: A Disk Galaxy Forms
Video Credit:
TNG Collaboration, MPCDF, FAS Harvard U.; Music: World's Sunrise (YouTube: Jimena Contreras)

How did we get here? We know that we live on a planet orbiting a star orbiting a galaxy, but how did all of this form? Since our universe moves too slowly to watch, faster-moving computer simulations are created to help find out. Specifically, this featured video from the IllustrisTNG collaboration tracks gas from the early universe (redshift 12) until today (redshift 0). As the simulation begins, ambient gas falls into and accumulates in a region of relatively high gravity. After a few billion years, a well-defined center materializes from a strange and fascinating cosmic dance. Gas blobs -- some representing small satellite galaxies -- continue to fall into and become absorbed by the rotating galaxy as the present epoch is reached and the video ends. For the Milky Way Galaxy, however, big mergers may not be over -- recent evidence indicates that our large spiral disk Galaxy will collide and coalesce with the slightly larger Andromeda spiral disk galaxy in the next few billion years.
2023 June 1

Recycling Cassiopeia A
Image Credit:
X-ray - NASA, CXC, SAO; Optical - NASA,STScI

Massive stars in our Milky Way Galaxy live spectacular lives. Collapsing from vast cosmic clouds, their nuclear furnaces ignite and create heavy elements in their cores. After a few million years, the enriched material is blasted back into interstellar space where star formation can begin anew. The expanding debris cloud known as Cassiopeia A is an example of this final phase of the stellar life cycle. Light from the explosion which created this supernova remnant would have been first seen in planet Earth's sky about 350 years ago, although it took that light about 11,000 years to reach us. This false-color image, composed of X-ray and optical image data from the Chandra X-ray Observatory and Hubble Space Telescope, shows the still hot filaments and knots in the remnant. It spans about 30 light-years at the estimated distance of Cassiopeia A. High-energy X-ray emission from specific elements has been color coded, silicon in red, sulfur in yellow, calcium in green and iron in purple, to help astronomers explore the recycling of our galaxy's star stuff. Still expanding, the outer blast wave is seen in blue hues. The bright speck near the center is a neutron star, the incredibly dense, collapsed remains of the massive stellar core.
2023 June 2

Messier 101
Image Credit:
NASA, ESA, CFHT, NOAO;
Acknowledgement - K.Kuntz (GSFC), F.Bresolin (U.Hawaii), J.Trauger (JPL), J.Mould (NOAO), Y.-H.Chu (U. Illinois)

Big, beautiful spiral galaxy M101 is one of the last entries in Charles Messier's famous catalog, but definitely not one of the least. About 170,000 light-years across, this galaxy is enormous, almost twice the size of our own Milky Way. M101 was also one of the original spiral nebulae observed by Lord Rosse's large 19th century telescope, the Leviathan of Parsontown. Assembled from 51 exposures recorded by the Hubble Space Telescope in the 20th and 21st centuries, with additional data from ground based telescopes, this mosaic spans about 40,000 light-years across the central region of M101 in one of the highest definition spiral galaxy portraits ever released from Hubble. The sharp image shows stunning features of the galaxy's face-on disk of stars and dust along with background galaxies, some visible right through M101 itself. Also known as the Pinwheel Galaxy, M101 lies within the boundaries of the northern constellation Ursa Major, about 25 million light-years away.
2023 June 3

Charon: Moon of Pluto
Image Credit:
NASA, Johns Hopkins Univ./APL, Southwest Research Institute, U.S. Naval Observatory

A darkened and mysterious north polar region known to some as Mordor Macula caps this premier high-resolution view. The portrait of Charon, Pluto's largest moon, was captured by New Horizons near the spacecraft's closest approach on July 14, 2015. The combined blue, red, and infrared data was processed to enhance colors and follow variations in Charon's surface properties with a resolution of about 2.9 kilometers (1.8 miles). A stunning image of Charon's Pluto-facing hemisphere, it also features a clear view of an apparently moon-girdling belt of fractures and canyons that seems to separate smooth southern plains from varied northern terrain. Charon is 1,214 kilometers (754 miles) across. That's about 1/10th the size of planet Earth but a whopping 1/2 the diameter of Pluto itself, and makes it the largest satellite relative to its parent body in the Solar System. Still, the moon appears as a small bump at about the 1 o'clock position on Pluto's disk in the grainy, negative,telescopic picture inset at upper left. That view was used by James Christy and Robert Harrington at the U.S. Naval Observatory in Flagstaff to discover Charon in June of 1978.
2023 June 4

Color the Universe
Image Credit:
Unknown, possibly C. Flammarion

Wouldn't it be fun to color in the universe? If you think so, please accept this famous astronomical illustration as a preliminary substitute. You, your friends, your parents or children, can print it out or even color it digitally. While coloring, you might be interested to know that even though this illustration has appeared in numerous places over the past 100 years, the actual artist remains unknown. Furthermore, the work has no accepted name -- can you think of a good one? The illustration, first appearing in a book by Camille Flammarion in 1888, is frequently used to show that humanity's present concepts are susceptible to being supplanted by greater truths.
2023 June 5

In the Center of the Trifid Nebula
Image Credit & Copyright:
Martin Pugh

What's happening at the center of the Trifid Nebula? Three prominent dust lanes that give the Trifid its name all come together. Mountains of opaque dust appear near the bottom, while other dark filaments of dust are visible threaded throughout the nebula. A single massive star visible near the center causes much of the Trifid's glow. The Trifid, cataloged as M20, is only about 300,000 years old, making it among the youngest emission nebulas known. The star forming nebula lies about 9,000 light years away toward the constellation of the Archer (Sagittarius). The region pictured here spans about 20 light years.
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2023 June 6

Star Eats Planet
Illustrative Video Credit:
K. Miller & R. Hurt (Caltech, IPAC)

It’s the end of a world as we know it. Specifically, the Sun-like star ZTF SLRN-2020 was seen eating one of its own planets. Although many a planet eventually dies by spiraling into their central star, the 2020 event, involving a Jupiter-like planet, was the first time it was seen directly. The star ZTF SLRN-2020 lies about 12,000 light years from the Sun toward the constellation of the Eagle (Aquila). In the featured animated illustration of the incident, the gas planet's atmosphere is first pictured being stripped away as it skims along the outskirts of the attracting star. Some of the planet's gas is absorbed into the star's atmosphere, while other gas is expelled into space. By the video's end, the planet is completely engulfed and falls into the star's center, causing the star's outer atmosphere to briefly expand, heat up, and brighten. One day, about eight billion years from now, planet Earth may spiral into our Sun.
2023 June 7

M94: A Double Ring Galaxy
Image Credit & Copyright:
Brian Brennan

Most galaxies don't have any rings of stars and gas -- why does M94 have two? First, spiral galaxy M94 has an inner ring of newly formed stars surrounding its nucleus, giving it not only an unusual appearance but also a strong interior glow. A leading origin hypothesis holds that an elongated knot of stars known as a bar rotates in M94 and has generated a burst of star formation in this inner ring. Observations have also revealed another ring, an outer ring, one that is more faint, different in color, not closed, and relatively complex. What caused this outer ring is currently unknown. M94, pictured here, spans about 45,000 light years in total, lies about 15 million light years away, and can be seen with a small telescope toward the constellation of the Hunting Dogs (Canes Venatici).
2023 June 8

Elephant's Trunk and Caravan
Image Credit & Copyright: Steve Cannistra (StarryWonders)

Like an illustration in a galactic Just So Story, the Elephant's Trunk Nebula winds through the emission region and young star cluster complex IC 1396, in the high and far off constellation of Cepheus. Seen on the left the cosmic elephant's trunk, also known as vdB 142, is over 20 light-years long. This detailed telescopic view features the bright swept-back ridges and pockets of cool interstellar dust and gas that abound in the region. But the dark, tendril-shaped clouds contain the raw material for star formation and hide protostars within. Nearly 3,000 light-years distant, the relatively faint IC 1396 complex covers a large region on the sky, spanning over 5 degrees. This rendition spans a 1 degree wide field of view though, about the angular size of 2 full moons. Of course the dark shapes below and to the right of the outstretched Elephant's Trunk, are known to some as The Caravan.
2023 June 9

Pandora's Cluster of Galaxies
Image Credit:
NASA, ESA, CSA, Ivo Labbe (Swinburne), Rachel Bezanson (University of Pittsburgh), Processing: Alyssa Pagan (STScI)

This deep field mosaicked image presents a stunning view of galaxy cluster Abell 2744 recorded by the James Webb Space Telescope's NIRCam. Also dubbed Pandora's Cluster, Abell 2744 itself appears to be a ponderous merger of three different massive galaxy clusters. It lies some 3.5 billion light-years away, toward the constellation Sculptor. Dominated by dark matter, the mega-cluster warps and distorts the fabric of spacetime, gravitationally lensing even more distant objects. Redder than the Pandora cluster galaxies many of the lensed sources are very distant galaxies in the early Universe, their lensed images stretched and distorted into arcs. Of course distinctive diffraction spikes mark foreground Milky Way stars. At the Pandora Cluster's estimated distance this cosmic box spans about 6 million light-years. But don't panic. You can explore the tantalizing region in a 2 minute video tour.
2023 June 10

Mars and the Beehive
Image Credit &
Copyright: Rolando Ligustri

This month, bright Mars and brilliant Venus are the prominent celestial beacons in planet Earth's western skies after sunset. Wandering through the constellation Cancer the Crab, the Red Planet was captured here on the evening of June 3 near the stars of open cluster Messier 44. Recognized since antiquity this nearby, naked-eye star cluster is also known as the Praesepe or the Beehive cluster. A swarm of stars all much younger than the Sun, the Beehive cluster is a mere 600 light-years distant. Seen with a yellowish hue, Mars is about 17 light-minutes away. On June 12/13 Venus will take its turn posing next to the stars of the Beehive cluster. But the dazzling light of Venus will make the Beehive stars difficult to see by eye alone.
2023 June 11

The Sun and Its Missing Colors
Image Credit:
Nigel Sharp (NSF), FTS, NSO, KPNO, AURA, NSF

Here are all the visible colors of the Sun, produced by passing the Sun's light through a prism-like device. The spectrum was created at the McMath-Pierce Solar Observatory and shows, first off, that although our white-appearing Sun emits light of nearly every color, it appears brightest in yellow-green light. The dark patches in the featured spectrum arise from gas at or above the Sun's surface absorbing sunlight emitted below. Since different types of gas absorb different colors of light, it is possible to determine what gasses compose the Sun. Helium, for example, was first discovered in 1868 on a solar spectrum and only later found here on Earth. Today, the majority of spectral absorption lines have been identified - but not all.
2023 June 12

The Largest Satellites of Earth
Image Credit & Copyright:
Tianyao Yang

What’s that near the Moon? It’s the International Space Station (ISS). Although the ISS may appear to be physically near the Moon, it is not — it is physically near the Earth. In low Earth orbit and circulating around our big blue marble about every 90 minutes, the ISS was captured photographically as it crossed nearly in front of the Moon. The Moon, itself in a month-long orbit around the Earth, shows a crescent phase as only a curving sliver of its Sun-illuminated half is visible from the Earth. The featured image was taken in late March from Shanghai, China and shows not only details of Earth's largest human-made satellite, but details of the cratered and barren surface of Earth's largest natural satellite. Over the next few years, humanity is planning to send more people and machines to the Moon than ever before.
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2023 June 13

Moons Across Jupiter
Image Credit:
NASA; ESA, JPL, Cassini Imaging Team, SSI; Processing: Kevin M. Gill

Jupiter's moons circle Jupiter. The featured video depicts Europa and Io, two of Jupiter's largest moons, crossing in front of the grand planet's Great Red Spot, the largest known storm system in our Solar System. The video was composed from images taken by the robotic Cassini spacecraft as it passed Jupiter in 2000, on its way to Saturn. The two moons visible are volcanic Io, in the distance, and icy Europa. In the time-lapse video, Europa appears to overtake Io, which is odd because Io is closer to Jupiter and moves faster. The explanation is that the motion of the fast Cassini spacecraft changes the camera location significantly during imaging. Jupiter is currently being visited by NASA's robotic Juno spacecraft, while ESA's Jupiter Icy Moons Explorer (JUICE), launched in April, is enroute.