A substance is anhydrous if it contains no water, for example, salts lacking their water of crystallisation. The way of achieving the anhydrous form differs from one substance to another.
A partial solar eclipse at its peak at 3:37 p.m. in Mesa on Oct. 23, 2014. The eclipse was visible over most of North America and covered 44 percent of the Arizona sun. Michael Chow/The Republic.
By the time the Great American Eclipse arrives next August, it will have been 38 years since the last total solar eclipse on the U.S. mainland, but Americans won't have to wait as long for a followup. A total solar eclipse will travel north through Mexico and across the eastern United States in April 2024. The next one to visit the West, however, will not arrive until August 2045. So for some, the Great American Eclipse may well be the experience of a lifetime.