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.

March 22, 1998
See Explanation.  Clicking on the picture will download 
 the highest resolution version available.

Sunspots: Magnetic Depressions
Credit: National Solar Observatory

Explanation: Our Sun has spots! These spots appear dark in photographs like the one above, but in fact sunspots are quite bright - they are just dark compared to the rest of the Sun. Sunspots are about the size of the Earth and frequently occur in groups, as shown above. Sunspots occur when a concentrated portion of the Solar magnetic field pokes through the surface. This field slows energy from entering the sunspot region, causing sunspots to appear cooler, darker, and lower than the surrounding surface. Sunspots typically last a few days before dissipating. The number of sunspots is always changing, generally going from a maximum to a minimum about every 5 ½ years. In fact, the Sun just passed a minimum two years ago. The Sun and sunspots should never be looked at directly.

Tomorrow's picture: Starbirth in NGC 1808

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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.