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.

2002 September 28
See Explanation.  Clicking on the picture will download
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X-Ray Rainbows
Credit: J. McClintock et al. (CfA), CXC, NASA

Explanation: A drop of water or prism of glass can spread out visible sunlight into a rainbow of colours. In order of increasing energy, the well known spectrum of colours in a rainbow runs red, orange, yellow, green, blue, indigo, violet. X-ray light too can be spread out into a spectrum ordered by energy ... but not by drops of water or glass. Instead, the orbiting Chandra X-ray Observatory uses a set of 540 finely ruled, gold gratings to spread out the x-rays, recording the results with digital detectors. The resulting x-ray spectrum reveals much about the compositions, temperatures, and motions within cosmic x-ray sources. This false colour Chandra image shows the x-ray spectrum of a star system in Ursa Major catalogued as XTE J1118+480 and thought to consist of a sun-like star orbiting a black hole. Unlike the familiar appearance of a prism's visible light rainbow, the energies here are ordered along radial lines with the highest energy x-rays near the centre and lowest energies near the upper left and lower right edges of the image. The central spiky region itself is created by x-rays from the source which are not spread out by the array of gratings.

Tomorrow's picture: The Clouds of Venus

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
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& Michigan Tech. U.