The sun's influence on earth
Besides the fact that the sun heats up the Earth, there are a few other clear influences.
As we saw on the photosphere-page, the number of solar spots isn't constant in time. In fact, between 1640 and 1700 there were virtually no sunspots at all. That period coincides with the `little ice age': It was much colder in that era. This might be coincidence, but it might also be causally related. This is yet unknown.
The Skylab satellite has measured how much energy the Sun radiates in total. That too appeared not to be constant, but variable with a few tenths of percentage points. This can have an influence on earth's climate.
The picture on the left was taken from the space shuttle, and shows
the northern lights as seen from space.
This shows that the Sun has a number of influences on earth. This, however, is nothing compared to what will happen in a few billion years...