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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.

See Explanation. Clicking on the picture will download the highest resolution version available.

Active Region 1002 on an Unusually Quiet Sun

Explanation: Why has the Sun been so quiet recently? No one is sure. Our Sun has shown few active regions -- that house even fewer associated sunspots -- for over a year now, and such a period of relative calm is quite unusual. What is well known is that our Sun is in a transitional period between solar cycles called a Solar Minimum , where solar activity has historically been reduced. The stark lack of surface tumult is unusual even during a Solar Minimum , however, and activity this low has not been seen for many decades. A few days ago, however, a bona-fide active region -- complete with sunspots --appeared and continues to rotate across the Sun's face. Visible above, this region, dubbed Active Region 1002 (AR 1002), was imaged in ultraviolet light yesterday by the SOHO spacecraft , which co-orbits the Sun near the Earth. Besides the tranquility on the Sun's surface, recent data from the Ulysses spacecraft , across the Solar System, indicate that the intensity of the solar wind blowing out from the Sun is at a fifty year low. Predictions hold, however, that our Sun will show more and more active region s containing more and more sunspots and flares until Solar Maximum occurs in about four years.

Date September 24, 2008
Credit Credit: SOHO Consortium , EIT , ESA , NASA
Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
A service of: ASD at NASA / GSFC,
NASA Science Activation & Michigan Tech. U.