The sun spins on its axis once every 27 days on average. Sunspots form when the sun's plasma interacts with its magnetic field, resulting in solar flares and various forms of solar storms. Sunspots appear to be hot, but they are really cold patches on the sun's surface, however the term "cold" is relative. They can become hot during periods of high activity. It is known that the sun's rotation influences the distribution of sunspots in time. That is, more spots tend to appear around the times of maximum heat about half way through each 22-year cycle. These two facts lead scientists to believe that something about the sun's rotation helps determine where on its surface sunspots will arise. Scientists use three different methods to estimate the age of the sun: direct measurement of how many times the moon has been destroyed (or at least made look like it has) by meteoroids; analysis of the abundance of certain minerals in meteorites; and calculation from the properties of stars similar to the sun. All these methods give us a sense of how long it has been since the sun was new. But they don't tell us exactly when that newness started. We know that the moon is always being replenished by debris from collisions with other objects (including the sun), so it cannot be used as a clock for measuring time. The Earth's geologic history can be used to estimate how long ago major changes occurred on the sun.