Mira variable stars are named after the red giant star Mira (omicron Ceti) in the constellation Cetus the Whale. Variable stars brighten, then dim, then brighten again. While astronomers have known of the existence of these dramatically changing stars for hundreds of years, the cause of their variability has been hard to identify. Now, two researchers at the Harvard-Smithsonian Center for Astrophysics have solved this long-standing mystery. The key, say Mark Reid and Joshua Goldston, is the formation of light-absorbing chemicals in the star’s gaseous atmosphere — the same chemicals found in sunscreen. “Long before there were professional astronomers, people looked at the heavens and noted that some stars seemed to vanish and then reappear,” says Reid. “Only now are we beginning to understand more fully why that happens.” Their findings were published in the April 1, 2002 issue of the Astrophysical Journal.