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NASA Astronomy Picture of the Day:

Globular star cluster Omega Centauri, also known as NGC 5139, is some 15,000 light-years away. The cluster is packed with about 10 million stars much older than the Sun within a volume about 150 light-years in diameter. It's the largest and brightest of 200 or so known globular clusters that roam the halo of our Milky Way galaxy. Though most star clusters consist of stars with the same age and composition, the enigmatic Omega Cen exhibits the presence of different stellar populations with a spread of ages and chemical abundances. In fact, Omega Cen may be the remnant core of a small galaxy merging with the Milky Way. Omega Centauri's red giant stars (with a yellowish hue) are easy to pick out in this sharp, color telescopic view.

Photo by Ignacio Diaz Bobillo

NASA Astronomy Picture of the Day:

What's going on near the center of our galaxy? To help find out, a newly detailed panorama has been composed that explores regions just above and below the galactic plane in radio and X-ray light. X-ray light taken by the orbiting Chandra Observatory is shown in orange (hot), green (hotter), and purple (hottest) and superposed with a highly detailed image in radio waves, shown in gray, acquired by the MeerKAT array. Interactions are numerous and complex. Galactic beasts such as expanding supernova remnants, hot winds from newly formed stars, unusually strong and colliding magnetic fields, and a central supermassive black hole are all battling in a space only 1000 light years across. Thin bright stripes appear to result from twisting and newly connecting magnetic fields in colliding regions, creating an energetic type of inner galactic space weather with similarities to that created by our Sun. Continued observations and study hold promise to not only shed more light on the history and evolution of our own galaxy -- but all galaxies.

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

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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".

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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

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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