Next APOD: 2009 December 31 - Dust and the Helix Nebula

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APOD: 2009 December 31 - Dust and the Helix Nebula

Dust and the Helix Nebula
NASA, JPL-Caltech, Kate Su (Steward Obs, U. Arizona) et al.

Explanation: Dust makes this cosmic eye look red. The eerie Spitzer Space Telescope image shows infrared radiation from the well-studied Helix Nebula (NGC 7293) a mere 700 light-years away in the constellation Aquarius. The two light-year diameter shroud of dust and gas around a central white dwarf has long been considered an excellent example of a planetary nebula, representing the final stages in the evolution of a sun-like star. But the Spitzer data show the nebula's central star itself is immersed in a surprisingly bright infrared glow. Models suggest the glow is produced by a dust debris disk. Even though the nebular material was ejected from the star many thousands of years ago, the close-in dust could be generated by collisions in a reservoir of objects analogous to our own solar system's Kuiper Belt or cometary Oort cloud. Formed in the distant planetary system, the comet-like bodies would have otherwise survived even the dramatic late stages of the star's evolution.

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Next APOD: 2009 December 29 - Rigel and the Witch Head Nebula

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APOD: 2009 December 29 - Rigel and the Witch Head Nebula

Rigel and the Witch Head Nebula
Credit & Copyright: Rogelio Bernal Andreo (Deep Sky Colors)

Explanation: Double, double toil and trouble; Fire burn, and cauldron bubble -- maybe Macbeth should have consulted the Witch Head Nebula. This suggestively shaped reflection nebula on the lower left is associated with the bright star Rigel, to its right, in the constellation Orion. More formally known as IC 2118, the Witch Head Nebula glows primarily by light reflected from Rigel. Fine dust in the nebula reflects the light. Pictured above, the blue color of the Witch Head Nebula and of the dust surrounding Rigel is caused not only by Rigel's blue color but because the dust grains reflect blue light more efficiently than red. The same physical process causes Earth's daytime sky to appear blue, although the scatterers in Earth's atmosphere are molecules of nitrogen and oxygen. Rigel, the Witch Head Nebula, and gas and dust that surrounds them lie about 800 light-years away.

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Next APOD: 2009 December 1 - NGC 6992: Filaments of the Veil Nebula

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APOD: 2009 December 1 - NGC 6992: Filaments of the Veil Nebula

NGC 6992: Filaments of the Veil Nebula
Credit & Copyright: Daniel Lopez (Observatorio del Teide)

Explanation: Wisps like this are all that remain visible of a Milky Way star. About 7,500 years ago that star exploded in a supernova leaving the Veil Nebula, also known as the Cygnus Loop. At the time, the expanding cloud was likely as bright as a crescent Moon, remaining visible for weeks to people living at the dawn of recorded history. Today, the resulting supernova remnant has faded and is now visible only through a small telescope directed toward the constellation of the Swan (Cygnus). The remaining Veil Nebula is physically huge, however, and even though it lies about 1,400 light-years distant, it covers over five times the size of the full Moon. In images of the complete Veil Nebula, studious readers should be able to identify the above filaments on the lower left. The above image is a mosaic from the 2.5-meter Isaac Newton Telescope at Roque de los Muchachos Observatory in the Canary Islands.

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Next APOD: 2009 November 15 - M57: The Ring Nebula

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APOD: 2009 November 15 - M57: The Ring Nebula

M57: The Ring Nebula
Credit: H. Bond et al., Hubble Heritage Team (STScI/AURA), NASA

Explanation: It looks like a ring on the sky. Hundreds of years ago astronomers noticed a nebula with a most unusual shape. Now known as M57 or NGC 6720, the gas cloud became popularly known as the Ring Nebula. It is now known to be a planetary nebula, a gas cloud emitted at the end of a Sun-like star's existence. As one of the brightest planetary nebula on the sky, the Ring Nebula can be seen with a small telescope in the constellation of Lyra. The Ring Nebula lies about 4,000 light years away, and is roughly 500 times the diameter of our Solar System. In this picture by the Hubble Space Telescope in 1998, dust filaments and globules are visible far from the central star. This helps indicate that the Ring Nebula is not spherical, but cylindrical.

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