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Giant Sunspot Group

This image has been digitally enhanced to increase circularity, to sharpen and colourise.

Astronomers have been surprised by the emergence on the Sun of one of the largest sunspot groups of modern times. At this stage of the 11-year sunspot cycle the number of sunspots is expected to be quite small, but instead the Sun has burst into a renewed flurry of magnetic activity, the current giant sunspot being large enough to swallow the Earth many times over.

A sunspot's area is measured in millionths of the area of the Sun's disc. The largest sunspot group observed in the twentieth century was that of April 1947 which covered over 6,000 millionths of the solar disc. The current sunspot group is one of the largest seen since 1947, rivalling a group seen in 2001.

Sunspots, at temperatures of about 4000 degrees Celsius, are some 2000 degrees cooler than the general surface of the Sun (photosphere). While appearing black on the Sun, they are in reality reddish if they could be viewed against a dark sky. A sunspot consists of a dark central area (umbra), surrounded by a somewhat hotter annulus (penumbra).

The spots are caused by the interaction of a strong magnetic field with the surrounding solar photosphere. The vertical magnetic field lines, deep below the sunspot, inhibit the transfer of heat from the general body of the Sun to the central region of a spot, resulting in the lower temperature of the umbra. Ultimately, however, some heat is transmitted to the outer parts of the umbra causing the components of the magnetic field to expand and rise to the Sun's surface where they become nearly horizontal and where the heat can be dissipated quickly, resulting in the formation of the penumbra.

The safest way to view the Sun is to focus its image onto a white card placed behind the eyepiece of a telescope or binoculars taking care not to look directly at the Sun through the instrument or even with the naked eye.

More images from Armagh here
Images from NASA

For further information contact: John McFarland at the Armagh Observatory, College Hill, Armagh, BT61 9DG. Tel.: 028-3752-2928; FAX: 028-3752-7174; jmfarm.ac.uk;


Last Revised: 2004 July 26th
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