| MadSci Network: Astronomy |
The aurora borealis (and its southern counterpart, the aurora australis) are a classic example of a little thing making a big splash.
Although seen here on Earth, aurorae start at the center of the solar system. The Sun is constantly blowing out a stream of protons and electrons, called the Solar Wind. After about three days those particles get near the Earth and hit the Earth's magnetic field. You can think of the Earth's magnetic field as coming out of the ground at the north pole, going around the Earth from north to south, and then going back in at the south pole. The particles that hit the magnetic field want to 'slide down' the field to the poles. When they do this, they eventually hit the Earth's atmosphere. Now these particles are moving very fast, and when they hit the air they slam into air atoms that make up our atmosphere, sometimes knocking loose more electrons. After a short time these free electrons get back together with their parent atoms, and when they do, the atoms give off light. This light is usually greenish, but is sometimes red as well (it depends on what kind of atom you have). When this happens to lots of atoms, you get lots of light--the aurorae. The amount of energy involved can sometimes be more than the entire United States uses!
The power in the aurora depends mostly on the strength of the solar wind. During an intense solar storm, the wind can intensify very strongly. This disrupts the Earth's magnetic field, causing compass needles to swing and can induce currents in power lines. There have indeed been power blackouts from strong solar activity, and satellites in orbit have to be protected as well. Not only that, but any planet with a magnetic field will get aurorae- Voyager saw them on Jupiter and Saturn!