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The sun and Space Weather

Solar Activity | Solar Flares | Coronal Mass Ejections | Solar Wind

Solar Activity

When we see the sun using a normal (white light) telescope it seems quiet. We see a bright yellow disk marked by dark patches called sunspots. Sunspots are regions where intense portions of the Sun's interior field break through the surface. They appear dark when contrasted against the sun's surface as they are cooler than their surroundings.

Warning: Never look directly at the sun. It can seriously damage your vision. Try some of the safer observing techniques listed on this site instead!!

This image shows Active Region 9169. This was the host of the largest sunspot group observed so far during the current solar cycle. On 23 September 2000, the sunspot area within the group spanned 2,140 millionths of the visible solar surface, an area a dozen times larger than the entire surface of the Earth! Image courtesy of SOHO/MDI team.

In reality, the Sun is very active on all length- and time-scales. The movie below illustrates the difference in the Sun's appearance when seen through different filters. The movie is made up of three different images and provides a journey through the Sun's atmosphere. The first is a white light image similar to the one on the left. This image shows the photosphere: the Sun's visible surface. Note the location of dark sunspots on the solar disk.

The second image was taken using a H-alpha filter. Solar flares are often observed using filters to isolate the light emitted by hydrogen atoms in the red region of the solar spectrum (the H-alpha spectral line).In this image we see dark filaments which represent material suspended above the photosphere by the action of magnetic fields. This region of the solar atmpshere is termed the chromosphere.

The third image shows the million degree solar corona. The image was taken using the soft X-ray telescope onboard the Japanese Yohkoh mission. This illustrates bright loops clustered in areas that correspond to the sunspot regions.This bright clusters of loops are called Active Regions. These are the source of much solar activity ultimately leading to space weather effects. The bright loops you can see are emitting radiation at a temperature of more than 2 million degrees. They appear bright in X-rays because the coronal plasma is trapped by the magnetic field which takes on loop strucutres as it emerges from the solar interior. These bright loops interact in the atmosphere, often leading to the release of huge amounts of energy (about 1025Watts) and/or the ejection of large clouds of plasma and magnetic field structures into space.

Download mpeg version of this movie (courtesy of Yohkoh Public Outreach Project)

In this way, solar activity can be divided up into certain phenomena. These are:

The ejected particles, magnetic fields and radiation from these events travel though space and lead to space weather effects at the Earth.

Solar Flares 

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