Solar weather

Ken Tapping, May 29, 2013

In the sky this week…

  • Jupiter, Venus and Mercury are close together in the sunset twilight. Such occurrences are quite rare and worth seeing.
  • Saturn rises before sunset and is well up in the east by dark.
  • The Moon will reach Last Quarter on the 31st.

Over the last few months the Sun has been moderately active, which has led to various media reports of solar storms and dire consequences. Many of these were inaccurate and sensationalistic. Here is some background to provide some context to future reports of things happening on the Sun.

The Sun is a big ball of hot gas, threaded with magnetic fields and with a nuclear fusion reactor in the middle. That is what provides the energy. These magnetic fields emerge through the surface as huge loops, loaded with plasma, gas so hot (millions of degrees) that its atoms are starting to come apart, leaving them electrically charged.

This combination of magnetic field and trapped plasma acts rather like elastic, or a spring. Just as in the case of elastic bands or springs, we can store energy in them by stretching, twisting or compressing them. Anyone who has played with elastic bands knows there is a limit to how much energy can be stored in one. We reach a point where the elastic starts to tear. It then snaps, releasing its stored energy on our fingers.

Those magnetic loops on the Sun are also stretched and twisted, and might get jammed hard against other loops. An enormous amount of energy can be stored in them, millions of hydrogen bombs’ worth. This situation can develop in two ways. The energy storage can reach a point where an explosive instability starts somewhere in the structure. This rapidly expands, releasing huge amounts of energy. Electrons are accelerated to almost the speed of light, making radio waves, which we can detect, high-energy X-rays and beams of high-energy protons and electrons. A chunk of the loop may be shot off into space. These explosions, the largest in our Solar System, are known as solar flares.

There is a rather lower-key possibility. As before, the loop gets more and more stressed, but this time, instead of a huge explosion, the loop snaps off at the bottom, catapulting itself off into space at a speed of thousands of kilometres a second. This is like stretching an elastic band, but this time, instead of taking it to its snapping point, we let go of one end, so that the band shoots off at high speed. We call these solar events “coronal mass ejections”, or CME’s. Somehow these have also become known as solar storms. A CME might happen when a loop is gradually stressed to snapping point, or the snapping might be triggered by a nearby disturbance, like a solar flare. They may happen spontaneously, or they may be triggered by something, just like avalanches.

Flares and CME’s will not sterilize the Earth. They have been business as usual for the Sun ever since it formed, 4.5 billion years ago, and we know life has been here on Earth for at least 2.5 billion years. Solar activity might pose direct health hazards for people in space or at high altitudes, but not for us on the ground. It is our technology and infrastructure that are highly vulnerable, and that is something that we can do something about.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9.

Telephone: 250-497-2300
Fax: 250-497-2355
E-mailken.tapping@nrc-cnrc.gc.ca

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