SunspotIn 1947, the largest sunspot group recorded was observed on the sun's southern hemisphere. Its size was estimated at 7 billion square miles, or an area of 6100 millionths of the Sun's visible hemisphere. Sunspots are areas of somewhat cooler surface than the surrounding solar gases, and appear as dark spots on the solar surface. Astronomers measure the sizes of sunspots as millionth fractions of the Sun's visible area. Typically, a big sunspot measures 300 to 500 millionths, whereas the entire surface area of the Earth is only 169 millionths of the solar disk. |