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NASA Astronomy Picture of the Day:

On Saturn, the rings tell you the season. On Earth, today marks an equinox, the time when the Earth's equator tilts directly toward the Sun. Since Saturn's grand rings orbit along the planet's equator, these rings appear most prominent -- from the direction of the Sun -- when the spin axis of Saturn points toward the Sun. Conversely, when Saturn's spin axis points to the side, an equinox occurs, and the edge-on rings are hard to see from not only the Sun -- but Earth. In the featured montage, images of Saturn between the years of 2020 and 2025 have been superposed to show the giant planet passing, with this year's equinox, from summer in the north to summer in the south. Yesterday, Saturn was coincidently about as close as it gets to planet Earth, and so this month the ringed giant's orb is relatively bright and visible throughout the night.

Photo by Imran Sultan

NASA Astronomy Picture of the Day:

Does the Sun set in the same direction every day? No, the direction of sunset depends on the time of the year. Although the Sun always sets approximately toward the west, on an equinox like tomorrow the Sun sets directly toward the west. After tomorrow's September equinox, the Sun will set increasingly toward the southwest, reaching its maximum displacement at the December solstice. Before tomorrow's September equinox, the Sun had set toward the northwest, reaching its maximum displacement at the June solstice. The featured time-lapse image shows seven bands of the Sun setting one day each month from 2019 December through 2020 June. These image sequences were taken from Alberta, Canada -- well north of the Earth's equator -- and feature the city of Edmonton in the foreground. The middle band shows the Sun setting during an equinox -- in March. From this location, the Sun will set along this same equinox band again tomorrow.

NASA Astronomy Picture of the Day:

rly risers around planet Earth have enjoyed a shining crescent Moon near brilliant Venus, close to the eastern horizon in recent morning twilight skies. And yesterday, on September 19, skygazers watching from some locations in Earth's northern hemisphere were also able to witness Venus, in the inner planet's waxing gibbous phase, pass behind the Moon's waning crescent. In fact, this telescopic snapshot was taken moments before that occultation of gibbous Venus by the crescent Moon began. The close-up view of the beautiful celestial alignment records Venus approaching part of the Moon's sunlit edge in clear daytime skies from the Swiss Alps. Tomorrow, the Sun will pass behind a New Moon. But to witness that partial solar eclipse on September 21, skygazers will need to watch from locations in planet Earth's southern hemisphere.

Photo by Luca Bartek

NASA Astronomy Picture of the Day:

A study in contrasts, this colorful cosmic skyscape features stars, dust, and glowing gas in the vicinity of NGC 6914. The interstellar complex of nebulae lies some 6,000 light-years away, toward the high-flying northern constellation Cygnus and the plane of our Milky Way Galaxy. Obscuring interstellar dust clouds appear in silhouette while reddish hydrogen emission nebulae, along with the dusty blue reflection nebulae, fill the cosmic canvas. Ultraviolet radiation from the massive, hot, young stars of the extensive Cygnus OB2 association ionize the region's atomic hydrogen gas, producing the characteristic red glow as protons and electrons recombine. Embedded Cygnus OB2 stars also provide the blue starlight strongly reflected by the dust clouds. The over one degree wide telescopic field of view spans about 100 light-years at the estimated distance of NGC 6914.

Photo by Tommy Lease

NASA Astronomy Picture of the Day:

A new visitor from the outer Solar System, comet C/2025 R2 (SWAN) also known as SWAN25B was only discovered late last week, on September 11. That's just a day before the comet reached perihelion, its closest approach to the Sun. First spotted by Vladimir Bezugly in images from the SWAN instrument on the sun-staring SOHO spacecraft, the comet was surprisingly bright but understandably difficult to see against the Sun's glare. Still close to the Sun on the sky, the greenish coma and tail of C/2025 R2 (SWAN) are captured in this telescopic snapshot from September 17. Spica, alpha star of the constellation Virgo, shines just beyond the upper left edge of the frame while the comet is about 6.5 light-minutes from planet Earth. Near the western horizon after sunset and slightly easier to see in binoculars from the southern hemisphere, this comet SWAN will pass near Zubenelgenubi, alpha star of Libra, on October 2. C/2025 R2 (SWAN) is scheduled to make its closest approach to our fair planet around October 20.

Photo by Team Ciel Austral

NASA Astronomy Picture of the Day:

Can you spot famous celestial objects in this image? 18th-century astronomer Charles Messier cataloged only two of them: the bright Lagoon Nebula (M8) at the bottom, and the colorful Trifid Nebula (M20) at the upper right. The one on the left that resembles a cat's paw is NGC 6559, and it is much fainter than the other two. Even harder to spot are the thin blue filaments on the left, from supernova remnant (SNR G007.5-01.7). Their glow comes from small amounts of glowing oxygen atoms that are so faint that it took over 17 hours of exposure with just one blue color to bring up. Framing this scene of stellar birth and death are two star clusters: the open cluster M21 just above Trifid, and the globular cluster NGC 6544 at lower left.

Photo by J. De Winter, C. Humbert, C. Robert & V. Sabet; Text: Ogetay Kayali (MTU)

NASA Astronomy Picture of the Day:

A newly discovered comet is already visible with binoculars. The comet, C/2025 R2 (SWAN) and nicknamed SWAN25B, is brightening significantly as it emerges from the Sun's direction and might soon become visible on your smartphone -- if not your eyes. Although the brightnesses of comets are notoriously hard to predict, many comets appear brighter as they approach the Earth, with SWAN25B reaching only a quarter of the Earth-Sun distance near October 19. Nighttime skygazers will also be watching for a SWAN25B-spawned meteor shower around October 5 when our Earth passes through the plane of the comet's orbit. The unexpectedly bright comet was discovered by an amateur astronomer in images of the SWAN instrument on NASA's SOHO satellite. The comet is currently best observed in southern skies but is slowly moving north. The featured image was captured at sunset three days ago just above the western horizon in Zacatecas, Mexico.

Photo by Daniel Korona

NASA Astronomy Picture of the Day:

How does your favorite planet spin? Does it spin rapidly around a nearly vertical axis, or horizontally, or backwards? The featured video animates NASA images of all eight planets in our Solar System to show them spinning side-by-side for an easy comparison. In the time-lapse video, a day on Earth -- one Earth rotation -- takes just a few seconds. Jupiter rotates the fastest, while Venus spins not only the slowest (can you see it?), but backwards. The inner rocky planets across the top underwent dramatic spin-altering collisions during the early days of the Solar System. Why planets spin and tilt as they do remains a topic of research with much insight gained from modern computer modeling and the recent discovery and analysis of hundreds of exoplanets: planets orbiting other stars.

NASA Astronomy Picture of the Day:

The steerable 60 foot diameter dish antenna of the One-Mile Telescope at Mullard Radio Astronomy Observatory, Cambridge, UK, is pointing skyward in this evocative night-skyscape. To capture the dramatic scene, consecutive 30 second exposures were recorded over a period of 90 minutes. Combined, the exposures reveal a background of gracefully arcing star trails that reflect planet Earth's daily rotation on its axis. The North Celestial Pole, the extension of Earth's axis of rotation into space, points near Polaris, the North Star. That's the bright star that creates the short trail near the center of the concentric arcs. But the historic One-Mile Telescope array also relied on planet Earth's rotation to operate. Exploring the universe at radio wavelengths, it was the first radio telescope to use Earth-rotation aperture synthesis. That technique uses the rotation of the Earth to change the relative orientation of the telescope array and celestial radio sources to create radio maps of the sky at a resolution better than that of the human eye.

Photo by Joao Yordanov Serralheiro

NASA Astronomy Picture of the Day:

September's total lunar eclipse is tracked across night skies from both the northern and southern hemispheres of planet Earth in these two dramatic timelapse series. In the northern hemisphere sequence (top panel) the Moon’s trail arcs from the upper left to the lower right. It passes below bright planet Saturn, seen under mostly clear skies from the international campus of Zhejiang University in China at about 30 degrees north latitude. In contrast, the southern hemisphere view from Lake Griffin, Canberra, Australia at 35 degrees south latitude, records the Moon’s trail from the upper right to the lower left. Multiple lightning flashes from thunderstorms near the horizon appear reflected in the lake. Both sequences were photographed with 16mm wide-angle lenses and both cover the entire eclipse, with the darkened red Moon totally immersed in Earth's umbral shadow near center. But the different orientations of the Moon’s path across the sky reveal the perspective shifts caused by the views from northern vs. southern latitudes.

Photo by Zhouyue Zhu

NASA Astronomy Picture of the Day:

The dark, inner shadow of planet Earth is called the umbra. Shaped like a cone extending into space, it has a circular cross section most easily seen during a lunar eclipse. And on the night of September 7/8 the Full Moon passed near the center of Earth's umbral cone, entertaining eclipse watchers around much of our fair planet, including parts of Antarctica, Australia, Asia, Europe, and Africa. Recorded from Zhangjiakou City, China, this timelapse composite image uses successive pictures from the total lunar eclipse, progressing left to right, to reveal the curved cross-section of the umbral shadow sliding across the Moon. Sunlight scattered by the atmosphere into Earth's umbra causes the lunar surface to appear reddened during totality. But close to the umbra's edge, the limb of the eclipsed Moon shows a distinct blue hue. The blue eclipsed moonlight originates as rays of sunlight pass through layers high in the upper stratosphere, colored by ozone that scatters red light and transmits blue. In the total phase of this leisurely lunar eclipse, the Moon was completely within the Earth's umbra for about 83 minutes.

Photo by Wang Letian

NASA Astronomy Picture of the Day:

It is one of the largest nebulas on the sky -- why isn't it better known? Roughly the same angular size as the Andromeda Galaxy, the Great Lacerta Nebula can be found toward the constellation of the Lizard (Lacerta). The emission nebula is difficult to see with wide-field binoculars because it is so faint, but also usually difficult to see with a large telescope because it is so great in angle -- spanning about three degrees. The depth, breadth, waves, and beauty of the nebula -- cataloged as Sharpless 126 (Sh2-126) -- can best be seen and appreciated with a long duration camera exposure. The featured image is one such combined exposure -- in this case taken over three nights in August through dark skies in Moses Lake, Washington, USA. The hydrogen gas in the Great Lacerta Nebula glows red because it is excited by light from the bright star 10 Lacertae, one of the bright blue stars just to the left of the red-glowing nebula's center. Most of the stars and nebula are about 1,200 light years distant. Jigsaw Universe: Astronomy Puzzle of the Day

Photo by Ian Moehring & Kevin Roylance