NASA Astronomy Picture of the Day:

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

NASA Astronomy Picture of the Day:

Most galaxies don't have any rings -- why does this galaxy have two? To begin, the bright band near NGC 1512's center is a nuclear ring, a ring that surrounds the galaxy center and glows brightly with recently formed stars. Most stars and accompanying gas and dust, however, orbit the galactic center in a ring much further out -- here seen near the image edge. This ring is called, counter-intuitively, the inner ring. If you look closely, you will see this the inner ring connects ends of a diffuse central bar that runs horizontally across the galaxy. These ring structures are thought to be caused by NGC 1512's own asymmetries in a drawn-out process called secular evolution. The gravity of these galaxy asymmetries, including the bar of stars, cause gas and dust to fall from the inner ring to the nuclear ring, enhancing this ring's rate of star formation. Some spiral galaxies also have a third ring -- an outer ring that circles the galaxy even further out.

NASA Astronomy Picture of the Day:

On certain dates in February, an elusive firefall can be spotted at sunset in Yosemite National Park, when water flows, the weather cooperates and the direction to the setting Sun is just right. Often photographed from vantage points below, at the right moment the park's seasonal Horsetail Fall is isolated in the shadows of the steep walls of El Capitan. Then, still illuminated with rays of reddened sunlight the waterfall briefly takes on a dramatic, fiery appearance. But a Horsetail firefall can be photographed by moonlight too. Even more elusive by moonlight, the firefall effect can also be seen when a bright Moon sets at the right direction along the western horizon. And skies were clear enough for this well-planned imaging of an ephemeral Horsetail firefall, lit by a bright gibbous Moon setting in the early morning hours of April 15.

Photo by Tara Mostofi

NASA Astronomy Picture of the Day:

This cosmic skyscape features glowing gas and dark dust clouds along side the young stars of NGC 3572. A beautiful emission nebula and star cluster it sails far southern skies within the nautical constellation Carina. Stars from NGC 3572 are toward top center in the telescopic frame that would measure about 100 light-years across at the cluster's estimated distance of 9,000 light-years. The visible interstellar gas and dust is part of the star cluster's natal molecular cloud. Dense streamers of material within the nebula, eroded by stellar winds and radiation, clearly trail away from the energetic young stars. They are likely sites of ongoing star formation with shapes reminiscent of the Tadpoles of IC 410 better known to northern skygazers. In the coming tens to hundreds of millions of years, gas and stars in the cluster will be dispersed though, by gravitational tides and by violent supernova explosions that end the short lives of the massive cluster stars.

Photo by Carlos Taylor

NASA Astronomy Picture of the Day:

Gorgeous spiral galaxy NGC 3521 is a mere 35 million light-years away, toward the northern springtime constellation Leo. Relatively bright in planet Earth's sky, NGC 3521 is easily visible in small telescopes but often overlooked by amateur imagers in favor of other Leo spiral galaxies, like M66 and M65. It's hard to overlook in this colorful cosmic portrait though. Spanning some 50,000 light-years the galaxy sports characteristic patchy, irregular spiral arms laced with dust, pink star forming regions, and clusters of young, blue stars. This deep image also finds NGC 3521 embedded in fainter, gigantic, bubble-like shells. The shells are likely tidal debris, streams of stars torn from satellite galaxies that have undergone mergers with NGC 3521 in the distant past.

Photo by Mark Hanson

NASA Astronomy Picture of the Day:

The early morning planet parade continues. Visible the world over, the planets Jupiter, Venus, Mars and Saturn have been lining up in the pre-dawn sky since mid-April. In the featured image taken last month, these planets were captured over the Step Pyramid of Djoser, a UNESCO World Heritage Site. Located in the Saqqara necropolis of Egypt, the pyramid was constructed in the 27th century BC and is one of the oldest pyramids known. The two-image composite includes a foreground image taken during evening blue hour, and a background image captured from the same location the following morning. The morning planet line-up is slowly changing. At the end of last month, planets Jupiter and Venus switched places, while at the end of this month, Jupiter and Mars will switch after passing within one-degree of each other. Of course, this picturesque planetary angular alignment is a coincidence, as all of these worlds continue to orbit the Sun as they have for billions of years, well before even the ancient Pyramid of Djoser was built. Notable Submissions to APOD: Morning Planet Parade 2022

Photo by Osama Fatehi

NASA Astronomy Picture of the Day:

That's no comet. Below the Pleiades star cluster is actually a planet: Mercury. Long exposures of our Solar System's innermost planet may reveal something unexpected: a tail. Mercury's thin atmosphere contains small amounts of sodium that glow when excited by light from the Sun. Sunlight also liberates these molecules from Mercury's surface and pushes them away. The yellow glow from sodium, in particular, is relatively bright. Pictured, Mercury and its sodium tail are visible in a deep image taken last week from La Palma, Spain through a filter that primarily transmits yellow light emitted by sodium. First predicted in the 1980s, Mercury's tail was first discovered in 2001. Many tail details were revealed in multiple observations by NASA's robotic MESSENGER spacecraft that orbited Mercury between 2011 and 2015. Tails, of course, are usually associated with comets.

Photo by Sebastian Voltmer

NASA Astronomy Picture of the Day:

What's happened to the Sun? Two days ago, parts of South America were treated to a partial solar eclipse -- where the Moon blocked out part of the Sun. The featured image shows an image of the partially eclipsed Sun through clouds as it was setting over Patagonia, Argentina. In the tilted image, Earth is toward the right. During the eclipse, the Moon moved partly between Earth and the Sun. Although a visually impressive sight, the slight dimming of surroundings during this partial eclipse was less noticeable than dimming created by a thick cloud. In about two weeks, all of South America and part of North America will experience a total lunar eclipse -- where the Earth moves completely between the Moon and the Sun. In about two years, a total solar eclipse will cross North America.

Photo by Aixa Andrada

NASA Astronomy Picture of the Day:

What does a black hole look like? To find out, radio telescopes from around the Earth coordinated observations of black holes with the largest known event horizons on the sky. Alone, black holes are just black, but these monster attractors are known to be surrounded by glowing gas. This first image resolves the area around the black hole at the center of galaxy M87 on a scale below that expected for its event horizon. Pictured, the dark central region is not the event horizon, but rather the black hole's shadow -- the central region of emitting gas darkened by the central black hole's gravity. The size and shape of the shadow is determined by bright gas near the event horizon, by strong gravitational lensing deflections, and by the black hole's spin. In resolving this black hole's shadow, the Event Horizon Telescope (EHT) bolstered evidence that Einstein's gravity works even in extreme regions, and gave clear evidence that M87 has a central spinning black hole of about 6 billion solar masses. Since releasing this featured image in 2019, the EHT has expanded to include more telescopes, observe more black holes, track polarized light,and is working to observe the immediately vicinity of the black hole in the center of our Milky Way Galaxy. This week is: Black Hole Week New EHT Results to be Announced: Next Thursday

NASA Astronomy Picture of the Day:

A mere 600 light-years away, M44 is one of the closest star clusters to our solar system. Also known as the Praesepe or the Beehive cluster its stars are young though, about 600 million years old compared to our Sun's 4.5 billion years. Based on similar ages and motion through space, M44 and the even closer Hyades star cluster in Taurus are thought to have been born together in the same large molecular cloud. An open cluster spanning some 15 light-years, M44 holds 1,000 stars or so and covers about 3 full moons (1.5 degrees) on the sky in the constellation Cancer. Visible to the unaided eye, M44 has been recognized since antiquity. Described as a faint cloud or celestial mist long before being included as the 44th entry in Charles Messier's 18th century catalog, the cluster was not resolved into its individual stars until telescopes were available. A popular target for modern, binocular-equipped sky gazers, the cluster's few yellowish tinted, cool, red giants are scattered through the field of its brighter hot blue main sequence stars in this telescopic group snapshot. Dramatic diffraction spikes highlighting the brighter cluster members were created with string crossed in front of the telescope's objective lens.

Photo by Drew Evans

NASA Astronomy Picture of the Day:

Sharp telescopic views of NGC 3628 show a puffy galactic disk divided by dark dust lanes. Of course, this portrait of the magnificent, edge-on spiral galaxy puts some astronomers in mind of its popular moniker, the Hamburger Galaxy. It also reveals a small galaxy nearby (below), likely a satellite of NGC 3628, and a very faint but extensive tidal tail. The drawn out tail stretches for about 300,000 light-years, even beyond the upper left edge of the frame. NGC 3628 shares its neighborhood in the local universe with two other large spirals M65 and M66 in a grouping otherwise known as the Leo Triplet. Gravitational interactions with its cosmic neighbors are likely responsible for creating the tidal tail, as well as the extended flare and warp of this spiral's disk. The tantalizing island universe itself is about 100,000 light-years across and 35 million light-years away in the northern springtime constellation Leo.

Photo by Wilhelm Michael Kasakow

NASA Astronomy Picture of the Day:

In the early hours of April 24 this bright Lyrid meteor flashed along the central Milky Way. For a moment, it cast a bright reflection across Lake Nian, Yunnan province, China. The annual Lyrid meteor shower, one of the oldest known, is active in late April, as our fair planet plows through dust left along the orbit of long-period comet Thatcher. The trail of the bright fireball points back toward the shower's radiant in the constellation Lyra high in the northern springtime sky and off the top of the frame. Just rising in that starry sky, light from a third quarter moon also cast a glow on the peaceful waters of the lake.

Photo by Jeff Dai