what is a magnetic field?

Why are magnetic fields so important on the Sun?

Magnets will attract any other magnetic material, but they will also affect anything with an electrical charge. Since most of the material in the Sun is ionised, the movement of material in and around the Sun is controlled by magnetic fields. That's why pictures of material in the Sun's atmosphere look so similar to our diagrams of a magnetic field.

Here is a spectacular movie from the satellite TRACE, which sees the ultraviolet light from the hot ionised gas in the solar atmosphere. Can you see how big the Earth is in comparison to the Sun?