The number of sunspots at any one time varies.A large spot group may consist of as many as 10 groups and 300 spots across the sun.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 25 days.The most persistent large spots, however, can survive for two to three months.
31 Careful observations and systematic studies of sunspots
A were made by ancient astronomers. B started in the early 17th century.
C were made by Galileo only. D could be made without a telescope.
32 Sunspots are cooler than the rest of the suns surface because
A they produce less energy. B they are buried in the sun.
C they are far away from magnetic fields.D they are close to magnetic fields.
33 The leading spot and the following spot are the names of
A two large sunspots. B a large spot and a small spot.
C the two spots in a spot pair.D the central core and the ring around it.
34 If an intense sunspot activity had occurred in 1857, the next one would have been in
A 1858. B 1862. C 1865. D 1868.
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