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.

August 27, 1999
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Chandra's First Light: Cassiopeia A
Credit Chandra X-ray Observatory, NASA

Explanation: Cosmic wreckage from the detonation of a massive star is the subject of this official first image from NASA's Chandra X-ray Observatory. The supernova remnant, known as Cassiopeia A, was produced when a star exploded around 300 years ago in this northern sky constellation. It is revealed here in unprecedented detail in the light of X-rays - photons with thousands of times the energy of visible light. Shock waves expanding at 10 million miles-per-hour are seen to have heated this 10 light-year diameter bubble of stellar debris to X-ray emitting temperatures of 50 million kelvins. The tantalizing bright speck near the bubble's center could well be the dense, hot remnant of the stellar core collapsed to form a newborn neutron star. With this and other first light images, the Chandra Observatory is still undergoing check out operations in preparation for its much anticipated exploration of the X-ray sky. Chandra was launched aboard the space shuttle Columbia in July.

Tomorrow's picture: X-Ray Pleiades

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/ GSFC
& Michigan Tech. U.