How's the space weather today? Quiet enough for a safe trip to the moon? Quiet enough to operate your GPS navigation system accurately? So active that it would crash your power grid? Like our everyday weather, space weather can change suddenly, become violent, and interfere with our lives.

Space weather is driven by the sun. The solar wind, a plasma of protons and electrons, streams out of the sun and changes the shape of Earth's magnetic field.

Near Earth's surface, this field is like the field of a giant bar magnet, as shown.

An aurora over Australia as seen from the space shuttle, whose tail is visible at the top left. (photo courtesy of NASA)