Astronomy Picture of the Day

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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.
2010 September 18

Opposite the Sun
Image Credit & Copyright: Babak Tafreshi (TWAN)
Explanation: Chances are the brightest star you've seen lately is actually planet Jupiter. Jupiter rules the sky in this labeled view of a starry September night from the Alborz mountains in Iran, complete with the trail of a red flashlight illuminating the mountain road. On September 21st (Universal Time) Jupiter will be at opposition, the point opposite the Sun along its orbit, rising just as the Sun sets. For this opposition, Jupiter will be slightly brighter and closer to planet Earth than in any year since 1963. Much fainter and also approaching its own opposition on September 21st, is the distant planet Uranus. Very near Jupiter on the sky, the fainter planet is easy to spot in binoculars (similar to the inset view), well above and right of brilliant Jupiter and about as bright as one of Jupiter's own Galilean moons. Remarkably close to the opposition of both planets, the point on the sky exactly opposite the Sun on September 23rd is marked the Vernal Equinox. On that date, a Full Moon will join the celestial scene. Of course, any Full Moon is also at opposition.

Tonight: International Observe the Moon Night

 

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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.
2010 September 19

Dark Clouds of the Carina Nebula
Credit: NASA, ESA, et al., & Hubble Heritage Team (STScI/AURA);
Acknowledgement: M. Livio (STScI) & N. Smith (UC Berkeley) Explanation: What dark forms lurk in the mists of the Carina Nebula? These ominous figures are actually molecular clouds, knots of molecular gas and dust so thick they have become opaque. In comparison, however, these clouds are typically much less dense than Earth's atmosphere. Pictured above is part of the most detailed image of the Carina Nebula ever taken, a part where dark molecular clouds are particularly prominent. The image has recently been retaken and then re-colored based on light emitted by oxygen. The entire Carina Nebula spans over 300 light years and lies about 7,500 light-years away in the constellation of Carina. NGC 3372, known as the Great Nebula in Carina, is home to massive stars and changing nebula. Eta Carinae, the most energetic star in the nebula, was one of the brightest stars in the sky in the 1830s, but then faded dramatically. Wide-field annotated and zoomable versions of the larger image composite are also available.


 

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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.
2010 September 20

Aurora Over Norway
Credit & Copyright: Ole Christian Salomonsen Explanation: Auroras can make spectacular sights. Photographed above last weekend, flowing multi-colored auroras helped illuminate a busy sky above Tromsø, Norway. Besides the spectacular aurora pictured above, the photographer caught three satellites streaks, one airplane streak, and a friend trying to capture the same sight. Although auroras might first appear to be moonlit clouds, they only add light to the sky and do not block background stars from view. Called northern lights in the northern hemisphere, auroras are caused by collisions between charged particles from the magnetosphere and air molecules high in the Earth's atmosphere. If viewed from space, auroras can be seen to glow in X-ray and ultraviolet light as well. Predictable auroras might occur a few days after a powerful magnetic event has been seen on the Sun.


 

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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.
2010 September 21

Starry Night Over the Rhone
Credit: Vincent van Gogh, Wikipedia; Acknowledgement: B. Schaefer (LSU) Explanation: How can the majesty of the night sky best be captured in a painting? This was a continual challenge for Vincent van Gogh, a famous painter in the late 1800s who pioneered stirring depictions of star filled skies into several of his works. Pictured above is van Gogh's Starry Night Over the Rhone, where the French town of Arles is depicted complete with gas lights reflecting off the Rhone river. van Gogh's night sky appears alive with turbulent stellar images contrasting with lofty dark blue hues. Above the river, one can discern the stars of the familiar Big Dipper asterism. Following a line connecting the two Big Dipper stars on the right, the North Star Polaris could be easily found, the height of which can then be estimated and actually gives the latitude where the painting was created.


 

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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.
2010 September 22

Discovery Rollout Shadow
Credit & Copyright: Nancy Atkinson (Universe Today) Explanation: Who goes there? Although the spotlighted figure in white might not be identifiable by itself, surely the huge shadow behind it makes its identity clear: the space shuttle. Specifically, it was the space shuttle Discovery being rolled out last March in preparation for launch. As captured above, an unusual monstrous shadow on passing fog was created during a picturesque night unveiling. While on the shuttle Crawler-Transporter, one of the largest tracked vehicles on Earth, the shuttle moved at about 2 km per hour from the main assembly building to the launch pad at NASA's Kennedy Space Center in Florida, USA. About a month later, in its penultimate planned mission, Discovery roared off the launch pad and delivered needed supplies and equipment to the International Space Station. Yesterday, Discovery reached Launch Pad 39A in preparation for its last planned mission.


 

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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.
2010 September 23

Equinox and the Iron Sun
Credit: NASA / Goddard / SDO AIA Team
Explanation: Today, the Sun crosses the celestial equator heading south at 03:09 Universal Time. Known as an equinox, this astronomical event marks the first day of autumn in the northern hemisphere and spring in the south. Equinox means equal night. With the Sun on the celestial equator, Earth dwellers will experience nearly 12 hours of daylight and 12 hours of darkness. Of course, in the north the days continue to grow shorter, the Sun marching lower in the sky as winter approaches. To celebrate the equinox, consider this view of the Sun in extreme ultraviolet light from the Sun staring Solar Dynamics Observatory. Recorded yesterday, the false-color image shows emission from highly ionized iron atoms. Loops and arcs trace the glowing plasma suspended in magnetic fields above solar active regions.


 

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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.
2010 September 24

Equinox and the Harvest Moon
Image Credit & Copyright: Tamás Ábrahám
Explanation: Did you enjoy the moonlight last night? The Full Moon closest to autumnal equinox and the beginning of Fall is traditionally known as the Harvest Moon, rising opposite the Sun and illuminating fields at harvest time after sunset. This year's northern hemisphere autumnal equinox occurred yesterday, September 23rd, at 03:09 Universal Time. The Moon was at its full phase a mere 6 hours later -- exceptionally close for a Harvest Moon! Of course, the Moon still shines brightly through the night in surrounding days. In this picture from September 22nd, the lunar orb dominates the sky above a ruined church in Zsámbék, Hungary . Shining nearby, the brightest star is actually Jupiter, also opposite the Sun, seen here through thin clouds just left of the church wall.

 

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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.
2010 October 13

Science Museum Hubble
Credit: ESA, Hubble Explanation: Will the Hubble Space Telescope (HST) end up in a museum? Probably not, as when it finally goes bust, current plans call for it to be de-orbited into an ocean. But this won't stop likenesses of the famous floating observatory from appearing in science museums around the globe, sometimes paired with amazing pictures it has taken. Pictured above, in a celebration of the 20th anniversary of the launching of Hubble, a replica of the telescope was given a picturesque setting in the Italian Istituto Veneto di Scienze, Lettere ed Arti in their beautiful and historic Palazzo Loredan. The scene there appears perhaps a bit surreal as the deep space imager appears over a terrestrial tile floor, surrounded by the busts of famous thinkers, and under arches reminiscent of Escher. If you're lucky, it may even be possible to find an exhibition of Hubble images near you. And if no HST model appears there, you could always build your own.


 

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2010 October 14

Clusters, Hartley, and the Heart
Credit & Copyright: Rogelio Bernal Andreo Explanation: An alluring Comet Hartley 2 cruised through planet Earth's night sky on October 8, passing within about a Full Moon's width of the famous double star cluster in Perseus. The much anticipated celestial photo-op was recorded here in a 3 frame mosaic with greenish comet and the clusters h and Chi Persei placed at the left. The well-chosen, wide field of view spans about 7 degrees. It extends across the constellation boundary into Cassiopeia, all the way to the Heart Nebula (IC 1805) at the far right. To capture the cosmic moment, a relatively short 5 minute exposure was used to freeze the moving comet in place, but a longer exposure with a narrow-band filter was included in the central and right hand frames. The narrow-band exposure brings out the fainter reddish glow of the nebula's atomic hydrogen gas, in contrast to the cometary coma's kryptonite green. In the past few days, comet watchers have reported that Hartley 2 has become just visible to the unaided eye for experienced observers from dark, clear sites. On October 20, the comet will make its closest approach to Earth, passing within about 17 million kilometers. On November 4, a NASA spacecraft will fly by the comet's small nucleus estimated to be only 1.5 kilometers in diameter.


 

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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.
2010 November 4

Night Lights
Credit: ISS Expedition 25, NASA Explanation: Constellations of lights sprawl across this night scene, but they don't belong in the skies of planet Earth. Instead, the view looks down from the International Space Station as it passed over the United States along the northern Gulf Coast on October 29. A Russian Soyuz spacecraft is docked in the foreground. Behind its extended solar panels, some 360 kilometers below, are the recognizable city lights of New Orleans. Looking east along the coast to the top of the frame finds Mobile, Alabama while Houston city lights stand out to the west, toward the bottom. North (left) of New Orleans, a line of lights tracing central US highway I55 connects to Jackson, Mississippi and Memphis, Tennessee. Of course, the lights follow the population centers, but not everyone lives on planet Earth all the time these days. November 2nd marked the first decade of continuous human presence in space on board the International Space Station.

EPOXI mission spacecraft encounters comet Hartley 2

 

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2010 November 5

Comet Hartley 2 Flyby
Credit: NASA, JPL-Caltech, UMD, EPOXI Mission Explanation: Follow these 5 frames clockwise starting from the top left to track the view from the EPOXI mission spacecraft as it approached, passed under, and then looked back at the nucleus of comet Hartley 2 on November 4. Its closest approach distance was about 700 kilometers. In fact, this encounter was the fifth time a spacecraft from planet Earth has imaged a comet close-up. But Hartley 2's nucleus is definitely the smallest one so far, its long axis spanning only about 2 kilometers (1.2 miles). Though Hartley 2 is small, these stunning images showing jets of dust and gas indicate an impressively active surface. The jets are seen originating from the rough surface areas, with sunlight illuminating the nucleus from the right. Remarkably, rough areas at both ends of the elongated nucleus are joined by a narrower, smooth waist. The EPOXI mission reuses the Deep Impact spacecraft that launched a probe impacting the nucleus of comet Tempel 1 in 2005.


 

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Astronomy Picture of the Day

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.
2013 January 12

Ten Billion Earths
Illustration Credit: NASA / Ames / JPL-Caltech Explanation: How common are Earth-sized planets? Quite common, according to extrapolations from new data taken by NASA's orbiting Kepler spacecraft. Current computer models are indicating that at least one in ten stars are orbited by an Earth-sized planet, making our Milky Way Galaxy the home to over ten billion Earths. Unfortunately, this estimate applies only to planets effectively inside the orbit of Mercury, making these hot-Earths poor vacation opportunities for humans. This histogram depicts the estimated fraction of stars that have close orbiting planets of various sizes. The number of Sun-like stars with Earth-like planets in Earth-like orbits is surely much less, but even so, Kepler has also just announced the discovery of four more of those.

Tomorrow's picture: beyond the Milky Way​
 

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Astronomy Picture of the Day

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.
2013 January 27

Comet McNaught Over Chile
Image Credit & Copyright: Stéphane Guisard Explanation: Comet McNaught of 2007 has been, so far, the most photogenic comet of our time. After making quite a show in the northern hemisphere in early 2007 January, the comet moved south and developed a long and unusual dust tail that dazzled southern hemisphere observers. In this image, Comet McNaught was captured above Santiago, Chile. The bright comet dominates on the left while part of its magnificent tail spreads across the entire frame. From this vantage point in the Andes Mountains, one looks up toward Comet McNaught and a magnificent sky, across at a crescent moon, and down on clouds, atmospheric haze, and the city lights. The current year -- 2013 -- holds promise to be even better for comets than 2007. In early March, Comet PANSTARRS is on track to become visible to the unaided eye, while at the end of the year Comet ISON shows possibilities that include casting a tail that spreads across the sky, breaking up, and even becoming one of the brightest comets in recorded history.

Tomorrow's picture: triple center
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