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 total solar eclipse visible from the continental United States was in 1979, and it was only over a corner of the Pacific Northwest. Something like this summerâs event, where so many people on land can see a total solar eclipse, is exceptionally rare â although the United States actually will experience another one, crossing an opposite diagonal swath of the country, in 2024.