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S ol ar B i noc ul ars
SUNSPOTS
Sunspots are dark spots that appear on the photosphere, or visible "surface" of the
Sun. They usually have a dark core, called the umbra, surrounded by a lighter border,
called the penumbra. They form when large disturbances in the Sun's magnetic field
cool portions of the photosphere. Sunspots are relatively cool, being only 6000°F
(3300°C) compared to the normal 10,000°F (5500°C) of the rest of the photosphere.
Although these spots appear to be almost black, they are actually quite bright. If it were
possible to remove a sunspot from the Sun and put it in the night sky, it would shine
brighter than the full moon. They only appears to be "dark" when compared to the rest
of the photosphere.
Sunspots can be big. Very big. They can range in size from 10 to 100,000 miles (16
to 160,000 km) in diameter. To put that into perspective, the Earth is only 8,000 miles
(12,800 km) in diameter!
Sunspots usually appear in pairs but can also appear in very large groups. They can last
from a few days to several weeks and can change their shape, size and number as they
slowly rotate across the face of the Sun. It will take about two weeks for a sunspot group
to cross the Sun. Try looking at the Sun every day and draw a picture of what you see. At
the end of the week, compare your drawings and you'll see how sunspots evolve.
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