Did you know that our very own Sun is a type of variable star? The energy sent out by the Sun varies over an 11-year cycle. And these tiny changes can affect Earth in a big way. For example, between 1645 and 1715, the Sun went through a low-energy period. At the same time Europe was hit by an extraordinary cold spell: the Thames River in London froze, glaciers spread in the Alps, and ice in the Northern Sea increased!