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.
The last time most Americans experienced a total solar eclipse was 1991. In 2017, over 500 million people will be able to observe the August 21, 2017 total solar eclipse, in partial or total form: 391 million in the U.S., 35 million in Canada, and 119 million in Mexico (plus Central America and parts of South America and northwestern Europe) .