NASA Astronomy Picture of the Day:

What are all those streaks across the background? Satellite trails. First, the foreground features picturesque rock mounds known as Pinnacles. Found in the Nambung National Park in Western Australia, these human-sized spires are made by unknown processes from ancient sea shells (limestone). Perhaps more eye-catching, though, is the sky behind. Created by low-Earth orbit satellites reflecting sunlight, all of these streaks were captured in less than two hours and digitally combined onto the single featured image, with the foreground taken consecutively by the same camera and from the same location. Most of the streaks were made by the developing Starlink constellation of communication satellites, but some are not. In general, the streaks are indicative of an increasing number of satellites nearly continuously visible above the Earth after dusk and before dawn. Understanding and removing the effects of satellite trails on images from Earth's ground-based cameras and telescopes is now important not only for elegant astrophotography, but for humanity's scientific understanding of the distant universe. Astrophysicists: Browse 2,800+ codes in the Astrophysics Source Code Library

Photo by Joshua Rozells

NASA Astronomy Picture of the Day:

The Whirlpool Galaxy is a classic spiral galaxy. At only 30 million light years distant and fully 60 thousand light years across, M51, also known as NGC 5194, is one of the brightest and most picturesque galaxies on the sky. The featured image is a digital combination of images taken in different colors by the Earth-orbiting Hubble Space Telescope, highlighting many sharp features. Anyone with a good pair of binoculars, however, can see this Whirlpool toward the constellation of the Hunting Dogs (Canes Venatici). M51 is a spiral galaxy of type Sc and is the dominant member of a whole group of galaxies. Astronomers speculate that M51's spiral structure is primarily due to its gravitational interaction with the smaller galaxy on the image left.

Photo by Bernard Miller

NASA Astronomy Picture of the Day:

Have you ever seen the Man in the Moon? This common question plays on the ability of humans to see pareidolia -- imagining familiar icons where they don't actually exist. The textured surface of Earth's full Moon is home to numerous identifications of iconic objects, not only in modern western culture but in world folklore throughout history. Examples, typically dependent on the Moon's perceived orientation, include the Woman in the Moon and the Rabbit in the Moon. One facial outline commonly identified as the Man in the Moon starts by imagining the two dark circular areas -- lunar maria -- here just above the Moon's center, to be the eyes. Surprisingly, there actually is a man in this Moon image -- a close look will reveal a real person -- with a telescope -- silhouetted against the Moon. This featured well-planned image was taken in 2016 in Cadalso de los Vidrios in Madrid, Spain. Do you have a favorite object that you see in the Moon?

Photo by Dani Caxete

NASA Astronomy Picture of the Day:

At night you can follow this road as it passes through the Dark Sky Alqueva reserve not too far from Alentejo, Portugal. Or you could stop, look up, and follow the Milky Way through the sky. Both stretch from horizon to horizon in this 180 degree panorama recorded on June 3. Our galaxy's name, the Milky Way, does refer to its appearance as a milky path in the sky. The word galaxy itself derives from the Greek for milk. From our fair planet the arc of the Milky Way is most easily visible on moonless nights from dark sky areas, though not quite so bright or colorful as in this image. The glowing celestial band is due to the collective light of myriad stars along the galactic plane too faint to be distinguished individually. The diffuse starlight is cut by dark swaths of the galaxy's obscuring interstellar dust clouds. Standing above the Milky Way arc near the top of this panoramic nightscape is bright star Vega, with the galaxy's central bulge near the horizon at the right.

Photo by David Cruz

NASA Astronomy Picture of the Day:

This colorful telescopic field of view features a trio of interacting galaxies almost 90 million light-years away, toward the constellation Virgo. On the right two spiky, foreground Milky Way stars echo the extragalactic hues, a reminder that stars in our own galaxy are like those in distant island universes. With sweeping spiral arms and obscuring dust lanes, the dominant member of the trio, NGC 5566, is enormous, about 150,000 light-years across. Just above it lies smaller, bluish NGC 5569. Near center a third galaxy, NGC 5560, is apparently stretched and distorted by its interaction with massive NGC 5566. The trio is also included in Halton Arp's 1966 Atlas of Peculiar Galaxies as Arp 286. Of course, such cosmic interactions are now appreciated as part of the evolution of galaxies.

Photo by Nicolas Rolland

NASA Astronomy Picture of the Day:

These cosmic clouds of gas and dust drift through rich star fields along the plane of our Milky Way Galaxy toward the high flying constellation Cygnus. They're too faint to be seen with the unaided eye though, even on a clear, dark night. Image data from a camera and telephoto lens using narrowband filters was used to construct this 10 degree wide field of view. The deep mosaic reveals a region that includes star forming dust clouds seen in silhouette against the characteristic glow of atomic hydrogen and oxygen gas. NGC 6888 is the standout emission nebula near the top. Blown by winds from an massive Wolf-Rayet star it's about 25 light-years across and known as the Crescent Nebula. A faint bluish curl just below center in the frame is also the signature of a Wolf-Rayet star. Burning fuel at a prodigious rate and near the end of their stellar lives, both stars will ultimately go out with a bang in a spectacular supernova explosion. Toward the right, a massive, young O type star powers the glow of Sh2-101, the Tulip Nebula.

Photo by Wolfgang Zimmermann

NASA Astronomy Picture of the Day:

What are those unusual streaks? Some images of planet Earth show clear bright streaks that follow the paths of ships. Known as ship tracks, these low and narrow bands are caused by the ship's engine exhaust. Water vapor condenses around small bits of exhaust known as aerosols, which soon grow into floating water drops that efficiently reflect sunlight. Ship tracks were first discovered in 1965 in Earth images taken by NASA's TIROS satellites. Multiple ship tracks are visible across the featured image that was captured in 2009 over the Pacific Ocean by the MODIS instrument on NASA's Terra satellite. Inspired by ship-tracks, some scientists have suggested deploying a network of floating buoys in the worlds' oceans that spray salt-aerosol containing sea-water into the air so that, with the help of the wind, streams of sunlight-reflecting clouds would also form. Why do this? These human-made clouds could reflect so much sunlight they might help fight global warming. Today is: World Oceans Day

NASA Astronomy Picture of the Day:

Do dragons fight on the altar of the sky? Although it might appear that way, these dragons are illusions made of thin gas and dust. The emission nebula NGC 6188, home to the glowing clouds, is found about 4,000 light years away near the edge of a large molecular cloud unseen at visible wavelengths, in the southern constellation Ara (the Altar). Massive, young stars of the embedded Ara OB1 association were formed in that region only a few million years ago, sculpting the dark shapes and powering the nebular glow with stellar winds and intense ultraviolet radiation. The recent star formation itself was likely triggered by winds and supernova explosions, from previous generations of massive stars, that swept up and compressed the molecular gas. Joining NGC 6188 on this cosmic canvas, visible toward the lower right, is rare emission nebula NGC 6164, also created by one of the region's massive O-type stars. Similar in appearance to many planetary nebulae, NGC 6164's striking, symmetric gaseous shroud and faint halo surround its bright central star near the bottom edge. This impressively wide field of view spans over 2 degrees (four full Moons), corresponding to over 150 light years at the estimated distance of NGC 6188.

Photo by Shaun Robertson

NASA Astronomy Picture of the Day:

Will our Milky Way Galaxy collide one day with its larger neighbor, the Andromeda Galaxy? Most likely, yes. Careful plotting of slight displacements of M31's stars relative to background galaxies on recent Hubble Space Telescope images indicate that the center of M31 could be on a direct collision course with the center of our home galaxy. Still, the errors in sideways velocity appear sufficiently large to admit a good chance that the central parts of the two galaxies will miss, slightly, but will become close enough for their outer halos to become gravitationally entangled. Once that happens, the two galaxies will become bound, dance around, and eventually merge to become one large elliptical galaxy -- over the next few billion years. Pictured here is a combination of images depicting the sky of a world (Earth?) in the distant future when the outer parts of each galaxy begin to collide. The exact future of our Milky Way and the entire surrounding Local Group of Galaxies is likely to remain an active topic of research for years to come.

NASA Astronomy Picture of the Day:

What's happening at the center of active galaxy 3C 75? The two bright sources at the center of this composite x-ray (blue)/ radio (pink) image are co-orbiting supermassive black holes powering the giant radio source 3C 75. Surrounded by multimillion degree x-ray emitting gas, and blasting out jets of relativistic particles the supermassive black holes are separated by 25,000 light-years. At the cores of two merging galaxies in the Abell 400 galaxy cluster they are some 300 million light-years away. Astronomers conclude that these two supermassive black holes are bound together by gravity in a binary system in part because the jets' consistent swept back appearance is most likely due to their common motion as they speed through the hot cluster gas at about 1200 kilometers per second. Such spectacular cosmic mergers are thought to be common in crowded galaxy cluster environments in the distant universe. In their final stages, the mergers are expected to be intense sources of gravitational waves.

NASA Astronomy Picture of the Day:

On May 31 tens of parallel meteor streaks were recorded in this 8 degree wide field of view of planet Earth's limb from space. The image is one of a series of 5 minute long observations by the orbiting Yangwang-1 space telescope. It was captured at 03:43 UT, near the peak of the Tau Herculid meteor shower. As predicted, the meteor shower was an active one this year, caused as Earth swept through a relatively dense stream of debris from disintegrating Comet 73P/Schwassmann-Wachmann 3, but was lacking bright meteors. Nearly all of the Tau Herculid meteors in the Yangwang-1 image are too faint to be detected by groundbased instruments. But on that date patient earthbound skywatchers under clear skies still enjoyed a memorable showing of the Tau Herculids.

Photo by Zhuoxiao Wang

NASA Astronomy Picture of the Day:

With this creative astro-collaboration you can follow the plane of our Milky Way Galaxy as it bridges northern and southern hemisphere skies. To construct the expansive composite nightscape, skies over Observatorio El Sauce in Chile (top) were imaged on the same date but 6 hours later than the skies over the Saint-Veran observatory in the French Alps. The 6 hour time-lag allowed Earth's rotation to align the Milky Way above domes at the two sites. All exposures were made with similar cameras and lenses mounted on simple tripods. A faint greenish airglow is visible in the dark Chilean sky that also features the Large and Small Magellanic Clouds near the observatory dome. In the French Alps light pollution is apparent, but the distant Andromeda Galaxy can still be spotted near the horizon in the northern night. On planet Earth the two observatories are separated by about 10,000 kilometers.

Photo by Maxime Oudoux