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Astronomy Picture Of the Day (APOD)
The Sloan Great Wall: Largest Known Structure
7.11.2007
What is the largest structure known? The answer might depend on how one defines "structure." A grouping of galaxies known as the Sloan Great Wall was discovered in the Sloan Digital Sky Survey and is a leading candidate.
An X Class Flare Region on the Sun
6.11.2007
Why does the Sun flare? Unpredictably, our Sun unleashes tremendous flares expelling hot gas into the Solar System that can affect satellites, astronauts, and power grids on Earth. This close up of an active region on the Sun that produced a powerful X-class flare was captured by the orbiting TRACE satellite.
Comet Holmes Grows a Tail
5.11.2007
Comet Holmes continues to be an impressive sight to the unaided eye. The comet has diminished in brightness only slightly, and now clearly appears to have a larger angular extent than stars and planets. Astrophotographers have also noted a distinctly green appearance to the comet's coma over the past week.
The Closest Galaxy: Canis Major Dwarf
4.11.2007
What is the closest galaxy to the Milky Way? The new answer to this old question is the Canis Major dwarf galaxy. For many years astronomers thought the Large Magellan Cloud (LMC) was closest, but its title was supplanted in 1994 by the Sagittarius dwarf galaxy.
Golden Comet Holmes
3.11.2007
Surprising Comet Holmes remains easily visible as a round, fuzzy cloud in the northern constellation Perseus. Skywatchers with telescopes, binoculars, or those that just decide to look up can enjoy the solar system's latest prodigy as it glides about 150 million kilometers from Earth, beyond the orbit of Mars.
Three Nebulae in Narrow Band
2.11.2007
Narrow band filters and a false-color palette give these three nebulae a stunning appearance against the cosmic canvas of the central Milky Way. All three are stellar nurseries about 5,000 light-years or so distant, toward the nebula rich constellation Sagittarius.
Peculiar Arp 87
1.11.2007
A cosmic bridge of stars, gas, and dust stretches for over 75,000 light-years and joins this peculiar pair of galaxies cataloged as Arp 87. The bridge is strong evidence that these two immense star systems have passed close to each other and experienced violent tides induced by mutual gravity.
Halloween and the Ghost Head Nebula
31.10.2007
Halloween's origin is ancient and astronomical. Since the fifth century BC, Halloween has been celebrated as a cross-quarter day, a day halfway between an equinox (equal day / equal night) and a solstice (minimum day / maximum night in the northern hemisphere). With our modern calendar, however, the real cross-quarter day will occur next week.
Comet Holmes Coma Expands
30.10.2007
Go outside tonight and see Comet Holmes. No binoculars or telescopes are needed -- just curiosity and a sky map. Last week, Comet 17P/Holmes underwent an unusual outburst that vaulted it unexpectedly from obscurity into one of the brightest comets in recent years.
A Telescopic View of Erupting Comet Holmes
29.10.2007
What's happened to Comet Holmes? A normally docile comet discovered over 100 years ago, Comet 17P/Holmes suddenly became nearly one million times brighter last week, possibly over just a few hours. In astronomical...
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