Solar Activity

Magnetism is the main force at work when it comes to the interaction between the Sun and the Earth.  The magnetic field of the Sun is the origin of solar activity.  The magnetosphere of the Earth helps protect it from the solar wind.  Now we will go into a little bit more detail as to how the Sun's activity works within the interplanetary magnetic field.

The coronal mass ejections and solar flares that come from the sun often hit the Earth's magnetopause.  This creates changes within the Earth's magnetic field.  The normal configuration of the field is disrupted, causing the particles within it to flow differently. This can be harmful to Earth, and cause damage to equipment and even humans.  (There will be more about this in the following pages.)

Solar flares are areas around sunspots that appear to brighten sharply through a telescope because of an enormous energy release.  They are distinguished from other solar activity in that they happen so suddenly.  They can last between a few minutes to a day and are extremely hot.  They have three phases:

Preflare phase--A prominence in the active region of a sunspot rises slowly

Onset--The Sun's magnetic field lines start to break and reconnect, releasing energy and causing the prominence to erupt more rapidly

Main--The field lines continue to reconnect and the field closes down
 

There are two ways that a solar flare can be observed, on the disk and on the limb.

When seen on the disk, a darkening appears and then a rising in an active region.  Then two bright areas appear as ribbons.  They expand rapidly and get extremely bright, and the ejection occurs at this point.

When seen on the limb, a bright point appears and develops into a beaming mass of emission.  During the onset, surges and sprays are often seen.

Here is an image of a solar flare on the limb...

                                    ...and here is an animation of one on the disk.  (It's the bright spot near the top of the Sun.)
 

Coronal mass ejections are large bubbles of gas that cause particles to be ejected into the solar wind.  They are often associated with erupting prominences, and are thought to be caused by an energy release that takes place in the Sun's magnetic field, but is observed in the corona.  They are sometimes associated with solar flares, and can then be thought of as the expansion of the flare into space.  It is likely that coronal mass ejections cause the Earth more damage than solar flares.  During an ejection, a bright loop appears to emit from the corona, followed by a darker cavity.  These move outward as an erupting prominence slowly moves through as a second loop.

Here is an image of a coronal mass ejection sequence:

This sequence was taken with a coronagraph which creates an artificial solar eclipse by blocking out the Sun with a black disk so that the corona is visible.  (To see an animation of some recent coronal mass ejections, check out the Recent Solar Events page!)