Donald Goldsmith is a frequent contributor to Natural History. Trained both as a research astronomer and as an attorney, he devoted himself to popularizing astronomy more thirty years ago. In the ensuing years he has watched the dark-matter hypothesis develop from speculation to confirmation. Goldsmith has written or co-written more than twenty books, including Connecting with the Cosmos (Sourcebooks, 2002) and, with Neil deGrasse Tyson, Origins: Fourteen Billion Years of Cosmic Evolution (Norton, 2004), which was the companion book to the PBS NOVA series. Among his recent contributions to Natural History are “Turn, Turn, Turn” (December 2006/January 2007) and “Ice Cycles” (March 2007), both of which explain how the slow but periodic wobbles in Earth’s journey through space may influence climate change. He lives in Berkeley, California.