Number 75 (Story #3), April 10, 1992 by Phillip F. Schewe and Ben Stein THE MAGNETIC HISTORY OF STARS can be pieced together from measurements of calcium radiation. The magnetic field of the nearest star, the Sun, can be monitored by counting sunspots or by measuring the splitting of certain spectral lines in the Sun's spectrum; the size of this "Zeeman splitting" is related to the size of the Sun's magnetic field. These methods don't work for faraway stars. Instead, calcium emission, which goes up with magnetic activity, is used as a substitute. With more than 25 years of data, astronomers have observed that some stars are undergoing periods of low magnetic activity, periods like the "Maunder minimum" when (in the late 1600's, the time of the Little Ice Age) our Sun had fewer sunspots and, as a consequence some believe, a slightly smaller brightness. Middle-aged stars like the Sun seem to spend about one third of their time in Maunder minima, the data show. Longer-term studies of stars' magnetic activity may thus tell us more about the history of the Sun and might provide insights into possible climate change here on Earth. (Astronomy, April 1992.)