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NASA Astronomy Picture of the Day:

What are those streaks across Orion? They are reflections of sunlight from numerous Earth-orbiting satellites. Appearing by eye as a series of successive points floating across a twilight sky, the increasing number of communications satellites, including SpaceX Starlink satellites, are causing concern among many astronomers. On the positive side, Starlink and similar constellations make the post-sunset sky more dynamic, satellite-based global communications faster, and help provide digital services to currently underserved rural areas. On the negative side, though, these low Earth-orbit satellites make some deep astronomical imaging programs more difficult, in particular observing programs that need images taken just after sunset and just before dawn. Planned future satellite arrays that function in higher orbits may impact investigations of the deep universe planned for large ground-based telescopes at any time during the night. The streaks across Orion are not from Starlink but rather satellites in high geosynchronous orbit. The featured picture, taken in 2019 December, is a digital combination of over 65 3-minutes exposures, with some images taken to highlight the background Orion Nebula, while others to feature the passing satellites. SatCon2 Wokshop 12-16 July 2021: Mitigating Satellite Constellations

NASA Astronomy Picture of the Day:

Whatever hit Mimas nearly destroyed it. What remains is one of the largest impact craters on one of Saturn's smallest round moons. Analysis indicates that a slightly larger impact would have destroyed Mimas entirely. The huge crater, named Herschel after the 1789 discoverer of Mimas, Sir William Herschel, spans about 130 kilometers and is featured here. Mimas' low mass produces a surface gravity just strong enough to create a spherical body but weak enough to allow such relatively large surface features. Mimas is made of mostly water ice with a smattering of rock - so it is accurately described as a big dirty snowball. The featured image was taken during the closest-ever flyby of the robot spacecraft Cassini past Mimas in 2010 while in orbit around Saturn. Interactive: Take a trek across Mimas

Photo by NASAJPL-CaltechSpace Science InstituteCassini

NASA Astronomy Picture of the Day:

Auroras usually occur high above the clouds. The auroral glow is created when fast-moving particles ejected from the Sun impact the Earth's magnetosphere, from which charged particles spiral along the Earth's magnetic field to strike atoms and molecules high in the Earth's atmosphere. An oxygen atom, for example, will glow in the green light commonly emitted by an aurora after being energized by such a collision. The lowest part of an aurora will typically occur about 100 kilometers up, while most clouds exist only below about 10 kilometers. The relative heights of clouds and auroras are shown clearly in the featured picture in 2015 from Dyrholaey, Iceland. There, a determined astrophotographer withstood high winds and initially overcast skies in an attempt to capture aurora over a picturesque lighthouse, only to take, by chance, the featured picture including elongated lenticular clouds, along the way. Follow APOD on Instagram in: English, Farsi, Indonesian, Persian, or Portuguese

Photo by Daniele Boffelli

NASA Astronomy Picture of the Day:

Why is the Moon so dusty? On Earth, rocks are weathered by wind and water, creating soil and sand. On the Moon, the history of constant micrometeorite bombardment has blasted away at the rocky surface creating a layer of powdery lunar soil or regolith. For the Apollo astronauts and their equipment, the pervasive, fine, gritty dust was definitely a problem. On the lunar surface in December 1972, Apollo 17 astronauts Harrison Schmitt and Eugene Cernan needed to repair one of their rover's fenders in an effort to keep the rooster tails of dust away from themselves and their gear. This picture reveals the wheel and fender of their dust covered rover along with the ingenious application of spare maps, clamps, and a grey strip of "duct tape".

NASA Astronomy Picture of the Day:

How does the Moon's appearance change during a total lunar eclipse? The featured time-lapse video was digitally processed to keep the Moon bright and centered during the 5-hour eclipse of 2018 January 31. At first the full moon is visible because only a full moon can undergo a lunar eclipse. Stars move by in the background because the Moon orbits the Earth during the eclipse. The circular shadow of the Earth is then seen moving across the Moon. The light blue hue of the shadow's edge is related to why Earth's sky is blue, while the deep red hue of the shadow's center is related to why the Sun appears red when near the horizon. Tomorrow, people living from southeast Asia, across the Pacific, to the southwest Americas may get to see a Blood Supermoon Total Lunar Eclipse. Here the term blood refers to the (likely) red color of the fully eclipsed Moon, while the term supermoon indicates the Moon's slightly high angular size -- due to being relatively close to the Earth in its slightly elliptical orbit. Details: Total Lunar Eclipse on 2021 May 26

NASA Astronomy Picture of the Day:

Expansive Utopia Planitia on Mars is strewn with rocks and boulders in this 1976 image. Constructed from the Viking 2 lander's color and black and white image data, the scene approximates the appearance of the high northern martian plain to the human eye. For scale, the prominent rounded rock near center is about 20 centimeters (just under 8 inches) across. Farther back on the right side of the frame the a dark angular boulder spans about 1.5 meters (5 feet). Also in view are two trenches dug by the lander's sampler arm, the ejected protective shroud that covered the soil collector head, and one of the lander's dust covered footpads at the lower right. On May 14, China’s Zhurong Mars rover successfully touchdown on Mars and has returned the first images of` its landing site in Utopia Planitia.

NASA Astronomy Picture of the Day:

In 1716, English astronomer Edmond Halley noted, "This is but a little Patch, but it shews itself to the naked Eye, when the Sky is serene and the Moon absent." Of course, M13 is now less modestly recognized as the Great Globular Cluster in Hercules, one of the brightest globular star clusters in the northern sky. Sharp telescopic views like this one reveal the spectacular cluster's hundreds of thousands of stars. At a distance of 25,000 light-years, the cluster stars crowd into a region 150 light-years in diameter. Approaching the cluster core upwards of 100 stars could be contained in a cube just 3 light-years on a side. For comparison, the closest star to the Sun is over 4 light-years away. The remarkable range of brightness recorded in this image follows stars into the dense cluster core. Distant background galaxies in the medium-wide field of view include NGC 6207 at the lower right.

Photo by Martin Dufour

NASA Astronomy Picture of the Day:

Normally faint and elusive, the Jellyfish Nebula is caught in this alluring scene. In the telescopic field of view two bright yellowish stars, Mu and Eta Geminorum, stand just below and above the Jellyfish Nebula at the left. Cool red giants, they lie at the foot of the celestial twin. The Jellyfish Nebula itself floats below and left of center, a bright arcing ridge of emission with dangling tentacles. In fact, the cosmic jellyfish is part of bubble-shaped supernova remnant IC 443, the expanding debris cloud from a massive star that exploded. Light from that explosion first reached planet Earth over 30,000 years ago. Like its cousin in astrophysical waters the Crab Nebula supernova remnant, the Jellyfish Nebula is known to harbor a neutron star, the remnant of the collapsed stellar core. Composed on April 30, this telescopic snapshot also captures Mars. Now wandering through early evening skies, the Red Planet also shines with a yellowish glow on the right hand side of the field of view. Of course, the Jellyfish Nebula is about 5,000 light-years away, while Mars is currently almost 18 light-minutes from Earth.

Photo by Jason Guenzel

NASA Astronomy Picture of the Day:

What celestial body wears the Necklace Nebula? First, analyses indicate that the Necklace is a planetary nebula, a gas cloud emitted by a star toward the end of its life. Also, what appears to be diamonds in the Necklace are actually bright knots of glowing gas. In the center of the Necklace Nebula are likely two stars orbiting so close together that they share a common atmosphere and appear as one in the featured image by the Hubble Space Telescope. The red-glowing gas clouds on the upper left and lower right are the results of jets from the center. Exactly when and how the bright jets formed remains a topic of research. The Necklace Nebula is only about 5,000 years old, spans about 5 light years, and can best be found with a large telescope toward the direction of the constellation of the Arrow (Sagitta).

NASA Astronomy Picture of the Day:

Is our Milky Way Galaxy this thin? Magnificent spiral galaxy NGC 4565 is viewed edge-on from planet Earth. Also known as the Needle Galaxy for its narrow profile, bright NGC 4565 is a stop on many telescopic tours of the northern sky, in the faint but well-groomed constellation Coma Berenices. This sharp, colorful image reveals the spiral galaxy's boxy, bulging central core cut by obscuring dust lanes that lace NGC 4565's thin galactic plane. An assortment of other background galaxies is included in the pretty field of view. Thought similar in shape to our own Milky Way Galaxy, NGC 4565 lies about 40 million light-years distant and spans some 100,000 light-years. Easily spotted with small telescopes, sky enthusiasts consider NGC 4565 to be a prominent celestial masterpiece Messier missed.

Photo by CFHT

NASA Astronomy Picture of the Day:

The clouds may look like an oyster, and the stars like pearls, but look beyond. Near the outskirts of the Small Magellanic Cloud, a satellite galaxy some 200 thousand light-years distant, lies 5 million year young star cluster NGC 602. Surrounded by natal gas and dust, NGC 602 is featured in this stunning Hubble image of the region. Fantastic ridges and swept back shapes strongly suggest that energetic radiation and shock waves from NGC 602's massive young stars have eroded the dusty material and triggered a progression of star formation moving away from the cluster's center. At the estimated distance of the Small Magellanic Cloud, the featured picture spans about 200 light-years, but a tantalizing assortment of background galaxies are also visible in this sharp multi-colored view. The background galaxies are hundreds of millions of light-years or more beyond NGC 602.

NASA Astronomy Picture of the Day:

Undulating bright ridges and dusty clouds cross this close-up of the nearby star forming region M8, also known as the Lagoon Nebula. A sharp, false-color composite of narrow band visible and broad band near-infrared data from the 8-meter Gemini South Telescope, the entire view spans about 20 light-years through a region of the nebula sometimes called the Southern Cliff. The highly detailed image explores the association of many newborn stars imbedded in the tips of the bright-rimmed clouds and Herbig-Haro objects. Abundant in star-forming regions, Herbig-Haro objects are produced as powerful jets emitted by young stars in the process of formation heat the surrounding clouds of gas and dust. The cosmic Lagoon is found some 5,000 light-years away toward the constellation Sagittarius and the center of our Milky Way Galaxy. (For location and scale, check out this image superimposing the close-up of the Southern Cliff within the larger Lagoon Nebula. The scale image is courtesy R. Barba'.)