Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2022 May 11

Gravity’s Grin

Image Credit: X-ray – NASA / CXC / J. Irwin et al. ; Optical – NASA/STScI

Explanation: Albert Einstein’s general theory of relativity, published over 100 years ago, predicted the phenomenon of gravitational lensing. And that’s what gives these distant galaxies such a whimsical appearance, seen through the looking glass of X-ray and optical image data from the Chandra and Hubble space telescopes. Nicknamed the Cheshire Cat galaxy group, the group’s two large elliptical galaxies are suggestively framed by arcs. The arcs are optical images of distant background galaxies lensed by the foreground group’s total distribution of gravitational mass. Of course, that gravitational mass is dominated by dark matter. The two large elliptical “eye” galaxies represent the brightest members of their own galaxy groups which are merging. Their relative collisional speed of nearly 1,350 kilometers/second heats gas to millions of degrees producing the X-ray glow shown in purple hues. Curiouser about galaxy group mergers? The Cheshire Cat group grins in the constellation Ursa Major, some 4.6 billion light-years away.

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2022 May 10

NGC 6334: The Cat’s Paw Nebula

Image Credit & Copyright: Stefan Steve Bemmerl & Team Wolfatorium (Hakos/Namibia)

Explanation: Nebulas are perhaps as famous for being identified with familiar shapes as perhaps cats are for getting into trouble. Still, no known cat could have created the vast Cat’s Paw Nebula visible toward the constellation of the Scorpion (Scorpius. At 5,500 light years distant, Cat’s Paw is an emission nebula with a red color that originates from an abundance of ionized hydrogen atoms. Alternatively known as the Bear Claw Nebula and cataloged as NGC 6334, stars nearly ten times the mass of our Sun have been born there in only the past few million years. Pictured here is a deep field image of the Cat’s Paw Nebula in light emitted by hydrogen, oxygen, and sulfur.

Explore Your Universe: Random APOD Generator

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2022 May 9

A Martian Eclipse: Phobos Crosses the Sun

Video Credit: NASA, JPL-Caltech, ASU MSSS, SSIExplanation: What’s that passing in front of the Sun? It looks like a moon, but it can’t be Earth’s Moon, because it isn’t round. It’s the Martian moon Phobos. The featured video was taken from the surface of Mars a month ago by the Perseverance rover. Phobos, at 11.5 kilometers across, is 150 times smaller than Luna (our moon) in diameter, but also 50 times closer to its parent planet. In fact, Phobos is so close to Mars that it is expected to break up and crash into Mars within the next 50 million years. In the near term, the low orbit of Phobos results in more rapid solar eclipses than seen from Earth. The featured video is shown in real time — the transit really took about 40 seconds,as shown. The videographer — the robotic rover Perseverance (Percy) — continues to explore Jezero Crater on Mars, searching not only for clues to the watery history of the now dry world, but evidence of ancient microbial life.

New Social Mirror: APOD now available on mastodon