As the sun sinks below the horizon at the South Pole, NOAA researchers stationed at the bottom of the world settle in for six months of darkness. Throughout the Antarctic winter, the researchers will collect air samples to help maintain long-term records of trace gases, aerosols, and solar radiation.
The Sun is the main source of power for the Earth's climate machine. Space-based measurements, begun in 1978, indicate Earth receives an average of 1,361 W/m<sup>2</sup> of incoming sunlight, and the amount varies by about one-tenth of a percent over the course of the 11-year solar cycle.
This is the first of nine lessons in the "Visualizing and Understanding the Science of Climate Change" website. This lesson is an introduction to Earth's climate and covers key principles regarding Earth's unique climate, atmosphere, and regional and temporal climate differences.