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Solar flares and explosions on earth both release energy.
Solar flares release a lot of energy - an awful lot of energy! How
much energy? To get an idea of how much energy is released in a
solar flare we need to compare them to some really big
explosions.
The biggest man-made explosions come from exploding thermonuclear bombs, so these are the best comparisons we have. Click on the movie symbol on the right handside. This is film of the US Army testing three different nuclear weapons near British owned Christmas Island in The Pacific Ocean. The first test, codenamed ADOBE, blew up a thermonuclear device on April 25, 1962, had a yield of 190 kilotons. That's quite a powerful explosion. The second test, codenamed FRIGATE BIRD, involved a warhead (yield not given) launched on May 6, 1962, from a submarine and carried to its target by a Polaris missile. The third tested an atomtic depth charge (20 kilotons), codenamed SWORDFISH, and was successfully detonated on May 11th 1962. |
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| Nature too as some pretty big explosions. Volcanoes release incredible amounts of energy. Here is a volcanic eruption in Iceland, under the Vatnajokull ice cap. On the right hand side is a picture of an eruption in 1996, which melted 800m of ice. On the right hand side is the crater which is left (by courtesy of Prof Bob White, Cambridge University). |
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This what the ice cap looked like afer the explosion. Imagine all the enrgy it took to get melt all that ice. But even a volcanic explosion is only about one 10 millionth the energy of a solar flare! |
| Most flares are quite short really, less than hour. Although we did see a flare once with the Japanese Yohkoh satellite which lasted 12 hours. | As powerful as the Sun's flares are, it's a bit of wimp when compared to flares on other stars - some of those flares are a thousand times more powerful than solar flares and can last as long as 10 days! |
This is what a flare looks like when we look at it in X-rays with the Yohkoh satellite. The image of the whole Sun on the left is a `soft' X-ray image taken with the Soft X-ray Telescope (SXT) on Yohkoh.
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The number of flares that we see depends on how active the Sun is.
The Sun is sometimes quiet while other times it's very active. There
is a rhythm to this activity, an eleven year cycle. At the moment the
Sun is just waking up and there are a lot of active regions around, so lots of flares as well.
The plot shows the variation of the Sun's X-ray radiation during Sep 1996. Can you see any flares? |
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This plot shows the same thing, except in Sep 1998. How many flares can you see?
It is clear that the numbers of flares which occur depends on the activity cycle of the Sun. This cycle can be seen clearly in the figure below. This shows images starting from the left (1991) and ending in 1995 (on the right). The number of bright regions dramatically changes with time. |
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