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.
Only those located in the path of the Moon's full shadow, its umbra, can see a total solar eclipse. The Moon's umbra travels eastward at about 1,700 km/h (1,056 mph). A total solar eclipse can last for several hours. Totality can range from a few seconds to 7.5 minutes. The longest total solar eclipse of the 21st century took place on July 22, 2009 when the totality lasted 6 minutes and 39 seconds. Total solar eclipses typically happen a little less than once a year when: