These pictures show the Sun's atmosphere (corona). The pictures were taken during two different solar eclipses. The picture at the top was taken in 1994 when there weren't many sunspots. The bottom picture was taken in 1980 when there were lots of sunspots. Can you see which picture has streamers near the Sun's poles?
Click on image for full size
Images courtesy of UCAR's High Altitude Observatory and Rhodes College.

The Solar Polar Atmosphere

Some of the time the Sun's atmosphere is very different over the Sun's poles from its atmosphere over its equator. The speed of the solar wind is also different at the poles.

Every 11 years or so the Sun has very few sunspots for a while. Scientists call these times "solar min" because the number of sunspots is at a minimum. During solar min, the Sun's atmosphere looks different from other times. The corona is the Sun's upper atmosphere. We can see the corona during a solar eclipse or by using a special instrument called a coronagraph. Pictures of the corona at solar min usually have streamers flowing away from the Sun's equator... but not from the poles!

The solar wind is a flow of particles (mostly electrons and protons) outward from the Sun. At solar min, the solar wind coming from the Sun's poles flows very fast. It zooms away from the Sun at speeds of 700 km/sec (435 miles/second) or faster. The solar wind coming from the Sun's equator is slower. It only goes about half as fast as the polar solar wind.

Sometimes there are lots of sunspots. Those times are called "solar max". Sunspots have very strong magnetic fields. When there are lots of sunspots, the Sun's magnetic field becomes a tangled mess. Eclipse photos and coronagraphs show streamers shooting out from all parts of the Sun... not just from the equator the way it is at solar min. Also, the solar wind is different at solar max. Both fast and slow solar winds can "blow" outward from all parts of the Sun.

A lot of our information about the Sun's poles came from one space mission. The Ulysses spacecraft "flew" over both of the Sun's poles. It is the only spacecraft so far that has "flown" over the poles of the Sun.

Last modified June 11, 2009 by Randy Russell.

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