Astronomy Picture of the Day

Discover the cosmos! Each day we feature a different image or photograph of our fascinating universe, along with a brief explanation written by a professional astronomer.

October 4, 1995

The Sun Spews X-rays
Credit: Yohkoh Soft X-ray Telescope, ISAS, Japan

Explanation: Our Sun is really very hot. The Sun's outer atmosphere is so hot that it emits much light in the X-ray band, which was unexpected. X-rays are usually emitted from objects having a temperature in the millions of degrees, not the mere thousands of degrees of the Sun's surface. The above X-ray picture shows the Sun one particularly active day in August of 1992. Evident are hot spots on the solar surface, showing that areas above the Sun's surface really do reach millions of degrees. But possibly more puzzling is the broader X-ray glow visible surrounding the Sun. This glow is now attributed to the Sun's X-ray corona, the origin of which is currently a subject of much discussion and debate. The Sun is one of the most photographed objects, with frequently updated pictures available over the WWW. In fact, an X-ray picture from Yohkoh taken earlier today is usually available over the WWW. Compare it to the above picture!

Tomorrow's picture: CG4: A Ruptured Cometary Globule

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Authors & editors: Robert Nemiroff (GMU) & Jerry Bonnell (USRA).
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