THE ASTRONOMY PICTURE OF DAY FOR 2011 February 26
Shell Galaxies in Pisces
Image Credit & Copyright: Stephen Leshin
Explanation: This colorful cosmic skyscape features a peculiar system of galaxies cataloged as Arp 227 some 100 million light-years distant. Swimming within the boundaries of the constellation Pisces, Arp 227 consists of the two galaxies prominent on the left; the curious shell galaxy NGC 474 and its blue, spiral-armed neighbor NGC 470. The faint, wide arcs or shells of NGC 474 could have been formed by a gravitational encounter with neighbor NGC 470. Alternately the shells could be caused by a merger with a smaller galaxy producing an effect analogous to ripples across the surface of a pond. Remarkably, the large galaxy on the right hand side of the deep image, NGC 467, appears to be surrounded by faint shells too, evidence of another interacting galaxy system. Intriguing background galaxies are scattered around the field that also includes spiky foreground stars. Of course, those stars lie well within our own Milky Way Galaxy. The field of view spans 25 arc minutes or about 1/2 degree on the sky.
THE ASTRONOMY PICTURE OF THE DAY FOR 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.
THE ASTRONOMY PICTURE OF THE DAY FOR 2010 September 3
The Small Cloud of Magellan + 47 TUCANAE + NGC 362
Credit & Copyright: Bogdan Jarzyna
Explanation: Portuguese navigator Ferdinand Magellan and his crew had plenty of time to study the southern sky during the first circumnavigation of planet Earth. As a result, two celestial wonders easily visible for southern hemisphere skygazers are known as the Clouds of Magellan. These cosmic clouds are now understood to be dwarf irregular galaxies, satellites of our larger spiral Milky Way Galaxy. The Small Magellanic Cloud actually spans 15,000 light-years or so and contains several hundred million stars. About 210,000 light-years away in the constellation Tucana, it is more distant than other known Milky Way satellite galaxies, including the Canis Major and Sagittarius Dwarf galaxies and the Large Magellanic Cloud. This sharp image also includes two foreground globular star clusters NGC 362 (bottom right) and 47 Tucanae. Spectacular 47 Tucanae is a mere 13,000 light-years away and seen here to the left of the Small Magellanic Cloud.
THE ASTRONOMY PICTURE OF THE DAY FOR 2010 August 31
The Annotated Galactic Center
Credit & Copyright: Jamie Fernandez
Explanation: The sky toward the center of our Galaxy is filled with a wide variety of celestial wonders, many of which are visible from a dark location with common binoculars. Constellations near the Galactic Center include Sagittarius, Libra, Scorpius, Scutum, and Ophiuchus. Nebulas include Messier objects M8, M16, M20, as well as the Pipe and Cat's Paw nebulas. Visible open star clusters include M6, M7, M21, M23, M24, and M25, while globular star cluster M22 is also visible. A hole in the dust toward the Galactic Center reveals a bright region filled with distant stars known as Baade's Window, which is visible between M7 and M8. Moving your cursor over the above image the will bring up an un-annotated version.
THE ASTRONOMY PICTURE OF THE DAY FOR 2010 February 2
Mars and a Colorful Lunar Fog Bow
Credit & Copyright: Wally Pacholka (AstroPics.com, TWAN)
Explanation: Even from the top of a volcanic crater, this vista was unusual. For one reason, Mars was dazzlingly bright two weeks ago, when this picture was taken, as it was nearing its brightest time of the entire year. Mars, on the far upper left, is the brightest object in the above picture. The brightness of the red planet peaked last week near when Mars reached opposition, the time when Earth and Mars are closest together in their orbits. Arching across the lower part of the image is a rare lunar fog bow. Unlike a more commonly seen rainbow, which is created by sunlight reflected prismatically by falling rain, this fog bow was created by moonlight reflected by the small water drops that compose fog. Although most fog bows appear white, all of the colors of the rainbow were somehow visible here. The image above was taken from high atop Haleakala, a huge volcano in Hawaii, USA.
THE ASTRONOMY PICTURE OF THE DAY FOR 2010 January 6
The Spotty Surface of Betelgeuse
Credit: Xavier Haubois (Observatoire de Paris) et al.
Explanation: Betelgeuse really is a big star. If placed at the center of our Solar System it would extend to the orbit of Jupiter. But like all stars except the Sun, Betelgeuse is so distant it usually appears as a single point of light, even in large telescopes. Still, astronomers using interferometry at infrared wavelengths can resolve the surface of Betelgeuse and reconstructed this image of the red supergiant. The intriguing picture shows two, large, bright, star spots. The spots potentially represent enormous convective cells rising from below the supergiant's surface. They are bright because they're hotter than the rest of the surface, but both spots and surface are cooler than the Sun. Also known as Alpha Orionis, Betelgeuse is about 600 light-years away.
BETELGEUSE (Alpha Orionis). The great star Betelgeuse is one of the two that dominate mighty Orion of northern winter, the other Rigel, the pair respectively also called Alpha and Beta Orionis. The name Betelgeuse is a corruption of the Arabic "yad al jauza," which means the "hand of al-jauza," al-jauza the ancient Arabs' "Central One," a mysterious woman. For us, it marks the upper left hand corner of the figure of the Greek's ancient hunter (and since he depicted is facing you, his right shoulder). One of the sky's two first magnitude supergiants (the other Antares), Betelgeuse is one of the larger stars that can be seen, indeed one of the larger stars to be found anywhere. Typically shining at visual magnitude 0.7 (ranking 11th in the sky), this class M (M1.5) red supergiant (with a temperature of about 3650 Kelvin) is a semi-regular variable that changes between magnitude 0.3 and 1.1 over multiple periods between roughly half a year and 6 years -- and possibly longer (and of course changing its rank). That may explain why Betelgeuse is the Alpha star even though it is generally fainter than Rigel. (On the other hand Bayer frequently also used position in lettering his stars.) The star's distance is a problem and a puzzle (true for all the other parameters as well). Direct parallax measures from space, using the most modern results, give 495 light years, whereas the parallax using the star's natural radio emission gives 640 light years. At a compromise distance of 570 light years, and allowing for a lot of infrared radiation and for absorption of light by circumstellar dust, the luminosity comes in at 85,000 times that of the Sun, considerably more than comes out of Antares. At the larger distance, luminosity boosts up to 105,000 Suns. From these and the temperature, we derive respective radii of 3.1 and 3.4 Astronomical Units, more than double the size of the Martian orbit. The star is so big that its angular diameter is easily measured. Indeed it was the first to have such a measure, of 0.047 seconds of arc, from which we find a true radius of between 4.1 (compromise distance) and 4.6 (larger distance) AU, considerably greater.(More recent measurements yield an angular diameter of 0.0547 arcseconds +/- 0.0003 ." However, the star is surrounded by a huge complex pattern of nested dust and gas shells, the result of eons of mass loss, that extends nearly 20,000 AU away (Betelgeuse so far having lost over a solar mass). That, an extended atmosphere, and the pulsations make it difficult to locate an actual "surface" to tell just how large the star actually is. Moreover, because of changes in gaseous transparency, the "size" of the star depends on the color of observation. Long-wave infrared measures give a vastly larger radius of up to 5 AU and greater, as big as the orbit of Jupiter, while shorter-wave infrared light gives as small as 3 AU. Moreover still, infrared measures reveal Betelgeuse to be shrinking (by some 15 percent over about 20 years), and other measures show that the star is not even round, but somewhat oval. Hubble observation also shows hot spots. It's no wonder that we find the various disagreements. It's more surprising that all agree as well as they DO. Whatever the actual numbers, Betelgeuse is clearly a highly evolved star, one whose central hydrogen fuel supply has run out. As a result, the core has contracted into a hot dense state, and the outer portions swelled outward. We do not really know the star's condition at the moment, but the odds are that it is now in the process of fusing helium into carbon and oxygen in its core. From theory, its initial mass should have fallen somewhere around 18 or 19 times that of the Sun. Starting life as hot, blue, class O star only around 10 million years ago, Betelgeuse will fuse elements through neon, magnesium, sodium, and silicon all the way to iron. The core will then collapse, causing the star to blow up as a supernova, most likely leaving a compact neutron star about the size of a small town behind. If it were to explode today, it would become as bright as a gibbous Moon, would cast strong shadows on the ground, and would be seen easily in full daylight. Birthplace was far away. The star's motion shows it to be a runaway member of the Orion OB1 association, particularly the subgroup that involves the stars up and to the right of the Belt.
The Paragraph above was Written by Jim Kaler 1998 FEB 20. Last updated 2009 JUNE 26. Return to STARS.
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THE ASTRONOMY PICTURE OF THE DAY FOR 2009 December 19
Aurora Shimmer, Meteor Flash
Credit & Copyright: Bjørnar G. Hansen,
Explanation: Northern Lights, or aurora borealis, haunted skies over the island of Kvaløya, near Tromsø Norway on December 13. This 30 second long exposure records their shimmering glow gently lighting the wintery coastal scene. A study in contrasts, it also captures the sudden flash of a fireball meteor from December's excellent Geminid meteor shower. Streaking past familiar stars in the handle of the Big Dipper, the trail points back toward the constellation Gemini, off the top of the view. Both aurora and meteors occur in Earth's upper atmosphere at altitudes of 100 kilometers or so, but aurora are caused by energetic charged particles from the magnetosphere, while meteors are trails of cosmic dust.
THE ASTRONOMY PICTURE OF THE DAY FOR 2009 December 9
HUDF 2009 Infrared: Dawn of the Galaxies
Credit: NASA, ESA, G. Illingworth (UCO/Lick & UCSC), R. Bouwens (UCO/Lick & Leiden U.), & the HUDF09 Team
Explanation: When did galaxies form? To help find out, the deepest near-infrared image of the sky ever has been taken of the same field as the optical-light Hubble Ultra Deep Field (HUDF) in 2004. The new image was taken this summer by the newly installed Wide Field Camera 3 on the refurbished Hubble Space Telescope. Faint red smudges identified on the above image likely surpass redshift 8 in distance.These galaxies therefore likely existed when the universe was only a few percent of its present age, and may well be members of the first class of galaxies. Some large modern galaxies make a colorful foreground to the distant galaxies. Analyses by the HUDF09 team indicate that at least some of these early galaxies had very little interstellar dust. This early class of low luminosity galaxies likely contained energetic stars emitting light that transformed much of the remaining normal matter in the universe from a cold gas to a hot ionized plasma.
BELOW IS A GREAT AMATEUR ASTRONOMER
PHOTO OF THE ORION NEBULA (M42) BY
MIKE DURKIN FROM LOCUST VALLEY, NY
Telescope: Stellarvue 70mm ED
Camera: Hutech modified Canon XT
Location: Locust Vally, NY on 2010 Jan 9
ISO: 400
Exposure: 10x180 seconds with dark frames subtracted.
Guiding: Shoestring adapters, PHD, and DSI Pro through a C8.
Processed with MaxDSLR and Photoshop
THE ASTRONOMY PICTURE OF THE DAY FOR 2009 November 27
The Jets of NGC 1097
Credit & Copyright: Robert Gendler
Explanation: Enigmatic spiral galaxy NGC 1097 lies about 45 million light-years away in the southern constellation Fornax. The small companion galaxy, just below and left of center, that seems to be wrapped in its spiral arms, is not NGC 1097's most peculiar feature though. Instead, This very deep exposure shows hints of faint, mysterious jets, most easily seen to extend well beyond the bright arms toward the lower right. In fact, four faint jets are ultimately recognized in optical images of NGC 1097. The jets trace an X centered on the galaxy's nucleus, but could be fossil trails left over from the capture of a much smaller galaxy in the large spiral's ancient past. A Seyfert galaxy, NGC 1097's nucleus also harbors a massive black hole.
THE ASTRONOMY PICTURE OF THE DAY FOR 2009 November 26
M78 Wide Field
Credit & Copyright: Thomas V. Davis (tvdavisastropix.com)
Explanation: Interstellar dust clouds and glowing nebulae abound in the fertile constellation of Orion. One of the brightest, M78, is centered in this colorful, wide field view, covering an area north of Orion's belt. At a distance of about 1,500 light-years, the bluish reflection nebula is around 5 light-years across. Its tint is due to dust preferentially reflecting the blue light of hot, young stars. Reflection nebula NGC 2071 is just to the left of M78. To the right of M78 and much more compact in appearance, the intriguing McNeil's Nebula is a recently recognized variable nebula associated with the formation of a sun-like star. The remarkably deep exposure also brings out the region's faint but pervasive reddish glow of atomic hydrogen gas.
THE ASTRONOMY PICTURE OF THE DAY FOR 2009 November 25
All-Sky Milky Way Panorama
Credit & Copyright: Axel Mellinger (Central Mich. U)
Explanation: If you could go far away from the Earth and look around the entire sky -- what would you see? Such was the goal of the All-Sky Milky Way Panorama 2.0 project of Axel Mellinger. Presented above is the result: a digital compilation of over 3,000 images comprising the highest resolution digital panorama of the entire night sky yet created. An interactive zoom version, featuring over 500 million pixels, can be found here. Every fixed astronomical object visible to the unaided eye has been imaged, including every constellation, every nebula, and every star cluster. Moreover, millions of individual stars are also visible, all in our Milky Way Galaxy, and many a thousand times fainter than a human can see. Dark filaments of dust lace the central band of our Milky Way Galaxy, visible across the image center. The satellite galaxies Large and Small Magellanic Clouds are visible on the lower right. This was not the first time Dr. Mellinger has embarked on such a project: the results of his first All-Sky Milky Way Panorama Project, taken using photographic film, are visible here.
THE ASTRONOMY PICTURE OF THE DAY FOR 2009 November 23
Crescent Earth in Nov 2009 from the Departing Rosetta Spacecraft
Credit & Copyright: ESA (MPS for OSIRIS Team), MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA
Explanation: Goodbye Earth. Earlier this month, ESA's interplanetary Rosetta spacecraft zoomed past the Earth on its way back across the Solar System. Pictured above, Earth showed a bright crescent phase featuring the South Pole to the passing rocket ship. Launched from Earth in 2004, Rosetta used the gravity of the Earth to help propel it out past Mars and toward a 2014 rendezvous with Comet Churyumov-Gerasimenko. Last year, the robot spacecraft passed asteroid 2867 Steins, and on 2010 July 10 it is scheduled to pass enigmatic asteroid 21 Lutetia. If all goes well, Rosetta will release a probe that will land on the 15-km diameter comet in 2014.
FROM WIKIPEDIA ON 21 LUTETIA:
21 Lutetia is a large main belt asteroid. It is an unusual form of M-type asteroid about 100 kilometers in diameter. The name Lutetia derives from the Latin name for Paris. Lutetia will be the object of a flyby by the Rosetta space probe on 2010 July 10th.
Lutetia was discovered on November 15, 1852 by Hermann Goldschmidt from the balcony of his apartment in Paris.[citation needed]
There have been two reported stellar occultations by Lutetia, observed from Malta in 1997 and Australia in 2003, with only one chord each, roughly agreeing with IRAS measurements.[citation needed]
On July 10, 2010, the European Rosetta space probe will pass Lutetia at a minimum distance of 3160 km and a velocity of 15 kilometres per second on its way to the comet 67P/Churyumov-Gerasimenko.[7] Lutetia will be the first M-type asteroid to be visited by a spacecraft.
The composition of Lutetia has puzzled astronomers for some time, and investigation has picked up in recent years in anticipation of the upcoming Rosetta flyby. While classified among the M-type asteroids, most of which are metallic, Lutetia is one of the anomalous members that do not display much evidence of metal on their surface. Indeed, there are various indications of a non-metallic surface: a flat, low frequency spectrum similar to that of carbonaceous chondrites and C-type asteroids and not at all like that of metallic meteorites,[8] a low radar albedo unlike the high albedos of strongly metallic asteroids like 16 Psyche,[6] evidence of hydrated materials on its surface,[9] abundant silicates,[10] and a thicker regolith than most asteroids.[11]
Lightcurve analysis indicates that Lutetia is a rough sphere with "sharp and irregular shape features" and that its pole points toward either ecliptic coordinates (β, λ) = (3°, 40°) or (β, λ) = (3°, 220°) with a 10° uncertainty.[4] This gives an axial tilt of 85°, or 89°, respectively, meaning that Lutetia spins at an approximately right angle to the ecliptic, like the planet Uranus.
21 Lutetia
Discovery
Designations
Physical characteristics
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