What are some historical observations of the Sun?

The Sun has been studied by humans for a long time. Eclipses were likely first recorded prior to 1948 B.C. Astronomers in China noticed sunspots several thousand years ago: the I-Ching or "Book of Changes," which dates back to the 12th century B.C., mentions a "Ri Zhong Jian Mei," which means "a obscuration was seen within the Sun". The first written record of a sunspot sighting dates to 28 B.C (by Chinese astronomers).

Telescopic observations of the Sun's surface began around 1610. It was at this time that the sunspots could be systematically observed and were, by Galileo, Fabricius, Scheiner and Harriot. For Galileo this was actually unlucky. Western religions expected the Sun to have no "blemishes" and the observations of sunspots did not further his career at all. He was forced to recant and placed under house arrest.

Nevertheless, observations of sunspots and the Sun continued. Around 1645 the sunspot count became very low until 1715. During these 70 years, there were likely less than 15 sunspots observed. These days, the minimum number observed per year is more like 15, even when the Sun is in its "inactive" phase. Interestingly, Europe had cooler than normal temperatures at this same time. So there is some indication that variations occurred in the Sun at the same time which cooled Earth's climate. This time period is referred to as the "Little Ice Age", and the sunspot absence as the Maunder Minimum.