A coronal mass ejection and prominence eruption observed in
white light from the SMM (Solar Maximum Mission) spacecraft. The time of each
panel increases from left to right.
The dashed inner circle in each panel is the solar radius, the occulting
radius is at 1.6 solar radii.
Click on image for full size
Image courtesy of the High Altitude Observatory, National Center for Atmospheric Research (NCAR), Boulder, Colorado.
The Sun is not a quiet place, but one that exhibits sudden
releases of energy.
One of the most frequently observed events are solar flares:
sudden, localized, transient increases in brightness
that occur in active regions near
sunspots. They are usually
most easily seen in H-alpha and X-rays, but may have effects
in the entire elecromagnetic spectrum. The X-ray brightness
from a large flare often exceeds the X-ray output from the rest of
the Sun. Another type of event, the coronal mass ejection,
typically disrupt helmet streamers
in the solar corona.
As much as 1e13 (10,000,000,000,000) kilograms of material can be
ejected into the solar wind. Coronal mass ejections propagate
out in the solar wind, where they may encounter the Earth
and influence geomagnetic activity. Coronal mass ejections are often
(but not always) accompanied by prominence eruptions, where
the cool, dense prominence material also erupts outward.
All of these forms of solar activity are believed to be driven by
energy release from the solar magnetic field. How this energy release
occurs, and the relationship between different types of solar activity,
is one of the many puzzles facing solar physicists today.
The amount of solar activity on the Sun is not constant, and is closely
related to the typical number of sunspots that are visible.
The number of sunspots and the levels of solar
activity vary with an 11 year period known as the
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