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Note: Distances are in kilometers.
Kilometers multiplied by 1.6093 = miles
Sunspots are relatively dark areas that sometimes appear on the surface of the Sun. They typically measure about 10,000 kilometers across, but in some cases very large ones (often in groups) can be seen with the naked eye (don't try it!). Ancient Chinese and other records show that spots have been seen when the sun's brightness is reduced by the Earth's atmosphere (near sunrise and sunset), by thin clouds, or by use of a filter known to be safe for viewing the sun. But it was only after 1610 when Galileo /1 and others observed the sun through telescopes that sunspots in large numbers were known to exist .
After 1611, with the aid of telescopes, up to 20 or 30 sunspots, some appearing in distinct groups, were seen daily for 18 years, with the exception of a few days. For many days in 1625, upwards of 50 spots were seen by observers from several countries in Europe. (Burritt) /2
Then, from about 1650 to 1670, very few sunspots were observed and from 1676 to 1684, no spots at all! Sun observers were mystified! This last period was later identified as the Maunder Sunspot Minimum that coincided with many years of extreme cold on Earth, especially in Europe. Since the Maunder Minimum, no similar absence of sunspots has occurred.
The day-to-day progression of spots made it clear that the sun was rotating from East to West, making one rotation in about 28+ days.
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