Circles of latitude are imaginary lines that run parallel to the equator, which is at 0 degrees latitude. These lines help to measure how far north or south a location is from the equator. Each circle of latitude is designated by degrees, with the North Pole at 90 degrees north and the South Pole at 90 degrees south. The most well-known circles of latitude include the Tropic of Cancer at 23.5 degrees north and the Tropic of Capricorn at 23.5 degrees south. These lines are important for understanding climate zones and navigation, as they help to define regions of the Earth.