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How does the sky turn dark at night? In stages, and with different characteristic colors rising from the horizon. The featured image shows, left to right, increasingly late twilight times after sunset in 20 different vertical bands. The picture was taken last month in Syracuse, Sicily, Italy, in the direction opposite the Sun. On the far left is the pre-sunset upper sky. Toward the right, prominent bands include the Belt of Venus, the Blue Band, the Horizon Band, and the Red Band. As the dark shadow of the Earth rises, the colors in these bands are caused by direct sunlight reflecting from air and aerosols in the Earth's atmosphere, multiple reflections sometimes involving a reddened sunset, and refraction. In practice, these bands can be diffuse and hard to discern, and their colors can depend on colors near the setting Sun. Finally, the Sun completely sets and the sky becomes dark. Don't despair -- the whole thing will happen in reverse when the Sun rises again in the morning.
2024-02-28 Dario Giannobile
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Centaurus is one of the most striking constellations in the southern sky. The Milky Way flows through this celestial expanse whose wonders also include the closest star system to the Sun, Alpha Centauri, and the largest globular star cluster in our galaxy, Omega Centauri (aka NGC 5139). This sharp telescopic view of Omega Centauri shows off the central regions of the cluster of about 10 million stars. Omega Cen itself is about 15,000 light-years away and 150 light-years in diameter - the largest of 150 or so known globular star clusters that roam the halo of our 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.
2007-04-19 Martin Pugh
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At sunset, Monday's western sky showed off stunning colors and dramatic clouds reflected in Brisbane Water on the Central Coast of New South Wales, Australia. It also featured the remarkable conjunction of the crescent Moon, Venus, and Jupiter forming a twilight smiley face. While the gathering of the two bright planets and Moon awed skygazers around planet Earth, astronomer Mike Salway reports taking special pains to record this gorgeous view, braving mosquitos and rain squalls along a soggy shore. His southern hemisphere perspective finds brilliant Venus at the highest point in the celestial grouping. For now, a bright pairing of Venus and Jupiter continues to dominate the western horizon after sunset but the Moon has moved on and tonight is near its first quarter phase.
2008-12-05 Mike Salway
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No one knows for sure what caused this signal. There is a slight possibility that it just might originate from an extraterrestrial intelligence. The bright colors on the blue background indicate that an anomalous signal was received here on Earth by a radio telescope involved in a Search for Extraterrestrial Intelligence (SETI). A search for these signals is ongoing by several groups including volunteer members of the SETI League. Time labels the vertical axis of the above plot, and frequency marks the horizontal axis. Although this strong signal was never positively identified, astronomers have identified in it many attributes characteristic of a more mundane and ultimately terrestrial origin. In this case, a leading possibility is that the signal originates from an unusual modulation between a GPS satellite and an unidentified Earth-based source. Many unusual signals from space remain unidentified. No signal has yet been strong enough or run long enough to be unambiguously identified as originating from an extraterrestrial intelligence.
2004-03-07 SETI League
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Place your cursor on this stunning view through dark skies over western Australia to highlight wonders of the southern Milky Way -- including the famous Southern Cross, the dark Coal Sack Nebula, and bright reddish emission regions surrounding massive star Eta Carinae. Recorded Tuesday at about 2 am, the thirty minute long color film exposure also captured a bright but mysterious object that moved slowly across the sky for over an hour. Widely seen, the object began as a small point and expanded as it tracked toward the North (left), resulting in a comet-like appearance in this picture. What was it? Reports are now identifying the mystery glow with a plume from the explosion of a malfunctioned Russian rocket stage partially filled with fuel. The rocket stage was marooned in Earth orbit after a failed communication satellite launch almost a year ago on February 28, 2006. A substantial amount of debris from the breakup can be tracked.
2007-02-22 Ray Palmer
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What would you see if you went right up to a black hole? Featured is a computer generated image highlighting how strange things would look. The black hole has such strong gravity that light is noticeably bent towards it - causing some very unusual visual distortions. Every star in the normal frame has at least two bright images - one on each side of the black hole. Near the black hole, you can see the whole sky - light from every direction is bent around and comes back to you. The original background map was taken from the 2MASS infrared sky survey, with stars from the Henry Draper catalog superposed. Black holes are thought to be the densest state of matter, and there is indirect evidence for their presence in stellar binary systems and the centers of globular clusters, galaxies, and quasars. Gallery: Thursday's Partial Solar Eclipse
2014-10-26 Alain Riazuelo
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Like Earth's moon, Saturn's largest moon Titan is locked in synchronous rotation. This mosaic of images recorded by the Cassini spacecraft in May of 2012 shows its anti-Saturn side, the side always facing away from the ringed gas giant. The only moon in the solar system with a dense atmosphere, Titan is the only solar system world besides Earth known to have standing bodies of liquid on its surface and an earthlike cycle of liquid rain and evaporation. Its high altitude layer of atmospheric haze is evident in the Cassini view of the 5,000 kilometer diameter moon over Saturn's rings and cloud tops. Near center is the dark dune-filled region known as Shangri-La. The Cassini-delivered Huygens probe rests below and left of center, after the most distant landing for a spacecraft from Earth.
2018-05-26
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Rehearsing for his historic flight on February 20, 1962, Mercury program astronaut John H. Glenn Jr. works in a cramped training capsule preparing for a few hours' voyage through space. Dubbed Friendship 7, his own snug spacecraft was launched by an Atlas rocket and carried Glenn three times around planet Earth at an altitude of about 120 miles, returning him safely to a "splashdown" in the Atlantic Ocean. The first American in orbit, Senator Glenn's remarkable return to space will be 36 years later as a payload specialist on the Space Shuttle Discovery mission STS-95. Discovery is a roomier craft which will carry a crew of 7 and an array of scientific payloads, such as the International Extreme Ultraviolet Hitchhiker. Scheduled for launch today at 2:00 PM Eastern Time, Discovery will orbit at an altitude of 320 miles and land after 8 days at Kennedy Space Center's shuttle landing facility. Godspeed the crew of STS-95 !
1998-10-29
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If Scorpius looked this good to the unaided eye, humans might remember it better. Scorpius more typically appears as a few bright stars in a well-known but rarely pointed out zodiacal constellation. To get a spectacular image like this, though, one needs a good camera, color filters, and a digital image processor. To bring out detail, the above image not only involved long duration exposures taken in several colors, but one exposure in a very specific red color emitted by hydrogen. The resulting image shows many breathtaking features. Vertically across the image left is part of the plane of our Milky Way Galaxy. Visible there are vast clouds of bright stars and long filaments of dark dust. Jutting out diagonally from the Milky Way in the image center are dark dust bands known as the Dark River. This river connects to several bright stars on the right that are part of Scorpius' head and claws, and include the bright star Antares. Above and right of Antares is an even brighter planet Jupiter. Numerous red emission nebulas and blue reflection nebulas are visible throughout the image. Scorpius appears prominently in southern skies after sunset during the middle of the year. Astrophysicists: Preview changes coming to the Astrophysics Source Code Library
2014-05-04 St�phane Guisard, TWAN
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Comet Hale-Bopp is spinning. The nucleus of the comet is a dirty snowball about 25 miles in diameter that spins about once every 12 hours. As Comet Hale-Bopp spins, parts of the comet's surface shoot away in jets. Ejected material therefore makes rings, which appear in above photograph as "hoods" in the coma. Even though the central part of Comet Hale-Bopp's coma is quite condensed, the nucleus is not visible. Comet Hale-Bopp is now headed south, away from the Sun, and is getting dimmer. At its brightest last week, it was even brighter than Comet Hyakutake was last year, although with a less prominent tail. Comet Hale-Bopp will still be easily visible to northern observers for several weeks in the northwest sky after sunset.
1997-04-14