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.

April 13, 1998
See Explanation.  Clicking on the picture will download 
 the highest resolution version available.

The Sun Changes
Credit: Learmonth Solar Observatory, IPS, USAF, NOAO

Explanation: Our Sun changes every day. This recent picture was taken in a very specific red color called Hydrogen-Alpha. Dark spots that might appear on the image are usually sunspots, dark magnetic depressions that are slightly cooler than the rest of the Sun's surface. Bright spots that might appear are usually plages, active regions that are slightly hotter than the rest of the Sun's surface. Over the next few years the average number of sunspots and plages will increase until "Solar Maximum" occurs in 2001. The Sun usually goes through a maximum and minimum every 11 years. From 1645 to 1715, however, almost no sunspots at all were recorded, for reasons unknown. (An updated picture can be found here.)

Tomorrow's picture: Starlight Reflections

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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.