The Antarctic Circle is an imaginary line of latitude around the earth at 66.5 degrees south of the equator. It is also commonly referred to as the Southern Polar Circle, the Antarctic Parallel or the Antarctic Polar Circle. This line marks the southernmost point on earth where the sun can be seen above the horizon for at least 24 hours during the summer solstice. The Antarctic Circle encompasses the continent of Antarctica, as well as parts of the Southern Ocean. It is an important boundary for scientists and explorers who study the effects of climate change on the polar regions.