Sunspots

It's not surprising that sunspots were observed by ancient astronomers. The largest sunspots on the sun can be seen without a telescope. It was not until the invention of the telescope in the early 17th century, however, that systematic studies of sunspots could be undertaken, The great astronomer Galileo was among the first to make telescopic observations of sunspots.

sunspots are frequently observed in pairs or in paired groups. The members if a spot pair are identified as the leading spot and the following spot. They are identified by their position in the pair in terms of the direction in which the sun rotates.

The number of sunspots at any one time varies. Sometimes there may be as many as 10 groups and 300spots across the sun. A large spot group may consist of as many 200 spots. The number of spots changes in a fairly regular pattern called the sunspot cycle. The largest number occurs about every 11 years. At sunspot minimum, there are at most just a few small spots.

The average lifetime of an individual spot group is roughly one solar rotation, which is about 25days. The most persistent large spots, however, can survive for two to three months.