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Changing magnetic fields on the Sun
About every 11th year the Sunís magnetic polarity changes. This means that the magnetic North Pole within a short period of time moves to the South Pole of the Sun and vice versa.

 
The change occurs in connection with the Sunís maximum. Last time this happened was in January 2001.
 
About the change in 2001:The compass needle of the Sun has turned

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Foto: ESA/NASA
Foto: ESA/NASA
In January 2001 the Sun passed through a remarkable, and also quite a rare change Ė the magnetic field of the Sun turned. If we had had a compass on the Sun, the compass needle would have turned 180 degrees! The magnetic field of the Sun stretches past the Earth and right out to the outer layers of our planetary system.

The Sunís magnetic North Pole, which was the Sunís northern hemisphere until a few months ago, pointed after the change towards the south. That the magnetic field was turned upside down is rare, but this was expected, and it was a signal that we were then in the middle of the Sunís maximum.

The image to the right shows the Sun as observed by the instrument EIT on board the SOHO satellite 15.02.2001.
EIT observes in ultraviolet light, and can ďseeĒ higher and warmer layers of the solar atmosphere.
 
Illustration: NASA
Illustration: NASA
Such changes always take place round the Sunís maximum and the magnetic field will not return until 2012, at the next Sunís maximum. The activity on the Sun varies with an 11-year cycle. At the Sunís maximum, as in the winter 2001, there are often many and large sunspots in combination with strong activity.

The curve of the illustration to the left shows the variation of the number of sunspots in relation to the time and the presupposed development of the number of sunspots during the next few years. When there are many sunspots this means that the Sun activity is high. The whole of the solar atmosphere then becomes active.

Frequent explosions on the Sun then project gigantic clouds of hot gas at a speed of several million km/h towards the Earth. These solar storms cause magnificent northern lights, but may also damage satellites, communication and even the electricity supply.

During the Sun maximum in 1989 several million Canadians experienced a power cut for many hours. As late as the summer 2000 several satellites were damaged by violent solar storms. The solar activity was at its highest during the winter 2001 and is expected to decrease strongly during the next few years.

The magnetic field of the Earth also changes polarity, but this occurs more seldom. There are from 5 000 to 50 million years between each change, last time was 740 000 years ago.
 
More about changing magnetic fields - some difficult reading for those who are especially interested
The Sunís magnetic field resembles that of the Earth, but it is 50 times stronger. At Sun maximum more spots frequently appear on the surface of the Sun and the magnetic field begins to change. Sunspots are places where intense magnetic loops Ė several hundred times stronger than the field that compasses the entire Sun Ė push their way through the surface of the Sun, the photosphere.

Currents on the surface of the Sun transport the magnetic fields from spots on more middle latitudes in the direction of the poles. The currents transport magnetic fields pointing southwards to the northern magnetic pole and magnetic fields pointing northwards towards the southern magnetic pole. This field is pointed opposite to the large magnetic field that the Sun has, and in this way this field constantly grows weaker. Right during the Sunís maximum the magnetic poles change polarity and begin growing in a new direction.
 
Butterfly diagram. Illustration: NASA
Butterfly diagram. Illustration: NASA
The illustration to the right is a so-called butterfly diagram that shows how the magnetic field of the Sun changes over time. Blue indicates the field pointing northwards, yellow the field pointing southwards. Click on the image in order to get a larger version.

At the poles the field changed direction about 1990 and in January 2001.
Closer to the equator of the Sun alterations also take place. The magnetic fields there are related to the sunspots. The strength of the magnetic field is given in the unit gauss. The strength of the magnetic field of the Earth is 0.6 gauss.
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This theme includes:
Reasons for the activities on the Sun
Sunspots
Read more about sunspots and magnetic fields
Flares Ė the most violent explosions of the solar system
Loops and magnetic short circuits
Protuberances Ė beautiful phenomena on the Sun
Other Sun phenomena
The magnetic field of the Earth
Auroral activity
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in co-operation with the Norwegian Space Centre, www.spacecentre.no.
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