These images show two Jupiter-sized sunspot groups on the face of the Sun (left) and an extreme close-up of a different, smaller sunspot group (right). The lefthand image was taken on Oct. 24, 2003 by the SOHO (Solar & Heliospheric Observatory) spacecraft. The righthand image was taken on July 15, 2002 by the Swedish 1-m Solar Telescope on the island of La Palma off the western coast of Africa. The central dark part of the large sunspot in the middle of the righthand image is about 14,000 km (8,700 miles) across... slightly larger than Earth!
Click on image for full size
Images courtesy SOHO (NASA & ESA) and the Royal Swedish Academy of Sciences.
Sunspots are dark, planet-sized regions
that appear on the "surface" of the Sun. Sunspots are "dark" because
they are cooler than their surroundings. A large sunspot might have a central
temperature of 4,000 K (about 3,700° C or 6,700° F), much lower than
the 5,800 K (about 5,500° C or 10,000° F) temperature of the adjacent photosphere.
Sunspots are only dark in contrast to the bright face of the Sun. If you could
cut an average sunspot out of the Sun and place
it elsewhere in the night sky, it would be about as bright as a full moon.
Sunspots have a lighter outer section called the penumbra, and a darker central
region named the umbra.
Sunspots are caused by disturbances in the Sun's
magnetic field welling up to the photosphere, the Sun's visible "surface".
The powerful magnetic fields
in the vicinity of sunspots produce active
regions on the Sun, which in turn frequently spawn disturbances such
as solar flares and Coronal
Mass Ejections (CMEs). Because sunspots are associated with solar
activity, space weather forecasters track these features in order to
help predict outbursts of "solar
Sunspots form over periods lasting from days to weeks, and can persist for
weeks or even months before dissipating. The average number of spots visible
on the face of the Sun is not constant, but varies in a multi-year cycle. Historical
records of sunspot counts, which go back hundreds of years, verify that
this sunspot cycle has an average
period of roughly eleven years.
Our Sun isn't the only star with spots. In recent years, astronomers have
been able to detect "starspots" - "sunspots" on other stars.
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