Americansolar astronomer. In 1889 he invented the spectroheliograph, which he used to study the Sun's prominences and surface features. In 1905 he found that sunspots were cooler than the surrounding photosphere, and in 1908 he showed from the Zeeman effect in their spectra that they had strong magnetic fields. In 1925 he found that the Sun's magnetic field reversed polarity in each successive sunspot cycle. Hale planned and organized funding for three telescopes, each of which was in turn the world's largest. The 40-inch (1-metre) refractor at Yerkes Observatory (still the largest refractor) was completed in 1897; the 100-inch (2.5-metre) Hooker Telescope at Mount Wilson Observatory in 1917; and the 200-inch (5-metre) reflector (later named the Hale Telescope) at Palomar Observatory in 1948.
Subjects: Science and Mathematics.