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Education and Outreach

UNDER STUDY

What is a solar flare? Solar flares are sudden releases of energy on the solar surface lasting several minutes to a few hours. Most of them cannot be seen by changes in their optical light, but only by light produced by specific elements such as hydrogen or calcium. Flares occur when magnetic fields on the Sun's surface get tangled and 'reconnect'. This is like rubber bands stretched taught being broken. This causes plasma near by to be heated to very high temperatures, sometimes exceeding 50 million degrees C. Solar flares can release more energy than thousands of hydrogen bombs. Although the most powerful 'X-class' flares are rare, the sun produces hundreds of micro-flares every day.

What is a plasma? A plasma is a type of gas in which many or most of the atoms are no longer electrically neutral and have been stripped of one or more of their electrons to become what are called 'ions'. This usually requires very high temperatures of several thousand degrees. The electrons and ions then become a gas which is capable of emitting many different types of electromagnetic radiation depending on its density and temperature, and whether a magnetic field is also present. All of the universe you see in the sky at night (stars) is dominated by plasmas. Plasma is the most common state of ordinary matter in the universe, out numbering the cool matter ( solid, liquid, gas) that you are familiar with by nearly 100 to 1. Most of the matter in the universe exists at temperature over 2000 K.

If the solar corona is so hot, why can't we see it? Because its density is so low. In fact, by a few million kilometers from the solar surface, the density of the corona is in the same as the vacuum inside a television picture tube. Even though the atoms have an temperature of 2 million degrees C, there are only a few hundred of them per cubic centimeter. Only in the inner corona closest to the solar surface are the conditions favorable for us to view the corona during an eclipse, even so, its brightness is overwhelmed by the light coming from the disk of the Sun itself where temperatures are far lower, but densities are millions of times higher.

Do solar flares affect computers? Not much, unless you are in space. We are pretty well shielded on the surface of Earth from solar flare effects. But in space, computer and electronic circuitry has to be carefully designed and shielded from solar flares, and there is much data...mostly classified...that describes in detail what the actual effects from solar flares are.

Can I hear solar activity on my short-wave radio? Historically, this was actually the way that solar flares were first discovered. The best way is to listen for short-wave drop outs caused by solar flares affecting the ionosphere. When solar flares erupt, the D-layer just below the daytime ionosphere becomes highly ionized and acts to absorb short-wave transmissions on long- path bounces. You can listen to distant stations, and when a flare happens, within 10 minutes the distant station 'drops-out' and becomes inaudible for several hours until the excess photoionization in the D-layer wanes to its normal level. This is a chemical process that takes time to proceed because of the very low densities of the gases at these altitudes. These drop-outs affect all short-wave bands in much the same way from 1 megahertz upwards to the ionosphere cutoff near 10 megahertz where it starts to become transparent to high frequency radio waves. Solar flares also produce several different classes of bursts of radio emission, but you need a radio telescope set-up with a very sensitive receiver and a 'dish' to detect them.

Why doesn't the Sun blow up? In fact, the Sun is doing a slow-motion explosion. It is shedding about 600 million tons every second in light energy, and it is loosing about one 100 trillionth of its mass every year in the so-called solar wind. But the sun will never blow up the way we think of a genuine explosion. It is the wrong kind of star to be either a nova or a supernova. The energy of the Sun, the thermonuclear fusion which produces all the heat and light, is occurring in the core of the Sun. The weight of all the mass in the Sun in the overlying layers is so enormous that the Sun is in an equilibrium state where the internal thermal pressure is balanced by the gravitational pressure directed inwards.

Could a massive solar flare destroy Earth? If the flare happened on the side of the Sun directly facing the Earth, the ozone layer would be destroyed completely and a huge amount of energy would be added to the upper atmosphere causing it to expand into space. Many satellites in Low Earth Orbit would re-enter the atmosphere, and most of the other satellites would be damaged by the huge increase in radiation exposure. Astronauts working in space would be instantly killed. Airline passengers might receive as much radiation exposure in a few hours as the normally would on the surface of earth for one or more years. But as for any impact to the biosphere, there wouldn't be much to worry about. During the last few million years, lunar rock samples show that there has not been a solar 'superflare' for at least this time, even though Earth has experienced literally millions of smaller flares during the same time. Superflares are not very common on G-type stars like the sun, but on M-type dwarfs called 'flare stars' they can outshine the star by over 1000 times!

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