Astronomers spend their lives looking at the stars, but all too aften the nearest star is neglected, the Sun.
The Sun is the very heart of the Solar System. Its light and heat enables life to exist on our planet. The Sun itself is physically enormous, spanning some 1.39 million kilometres in diameter (over 100 times greater than the Earth). Nevertheless, compared to other stars in our galaxy the Sun is relatively small and unremarkable. It lies on average 149.6 million kilometres from Earth and spans about 0.5 degrees in angular diameter as seen from our planet. As the Sun is gaseous its rotation period varies with latitude, with the equitorial region moving faster than at the poles. The average rotation period is 27.25 days.
The Sun shows a well defined cycle of activity that is referred to as the solar cycle. It was a German farther and son team of David and Johannes Fabricius who first published observations of sunspots in June 1611, a year before Galileo's similar observations.
Continuos support records exist from 1849 onward, around the time that the pattern of the solar cycle was first noticed. The cycle is defines by the amount of active regions visible on the disc, the number of which wax and wane in a regular pattern over approximately an 11-year period. For a typical cycle, smaller spots appear at higher latitudes and, as activity increases, the spot activity migrates toward the equator and during the maximum activity of the cycle they generally concerntrate around 15 degrees north and south of the solar equator.
Magnetism is the key to all this solar activity. Active regions of spots, huge and intricate prominences, loops and streamers at the chromosphere and coronal mass ejections are all shaped and driven magnetically. The solar cycle itself results from the recycling of magnetic fields from the movement of the material in the interior of the sun.