In science

The atomic number of gadolinium, a lanthanide

In astronomy,

Messier object M64, a magnitude 9.0 galaxy in the constellation Coma Berenices, also known as the Black Eye Galaxy.

The New General Catalogue object (http://www.ngcic.org/) NGC 64, a barred spiral galaxy in the constellation Cetus

The Saros number (http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros1-175.html) of the solar eclipse series which began on -832 April 11 and ended on 430 May 8. The duration of Saros series 64 was 1262.1 years, and it contained 71 solar eclipses.

The Saros number (http://sunearth.gsfc.nasa.gov/eclipse/LEsaros/LEsaros1-175.html) of the lunar eclipse series which began on -801 August 9 and ended on 714 February 4. The duration of Saros series 64 was 1514.5 years, and it contained 85 lunar eclipses.

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In other fields

Sixty-four is also:

In some computer programming languages, the size in bits of certain data types.
In China, "64 incident" refers to the Tiananmen Square protests of 1989 which happened on 4 June, 1989.
In chess or draughts, the total number of black (dark) and white (light) squares on the game board.
The code for international direct dial calls to New Zealand.
The designation of US Interstate 64, a freeway from Missouri to Virginia.
The subject of the Beatles song "When I'm Sixty-Four"
The registry of the U.S. Navy's aircraft carrier USS Constellation (CV-64)
The number of Braille characters in the old 6-dot system.
The year AD 64, 64 BC, or 1964.
In video games, the Nintendo 64 video game console and the Commodore 64. Since 1996, the number 64 is usually the abbreviation or slang for Nintendo 64.
The maximum number of strokes in any Chinese character.
Slang term referring to a 1964 Chevy Impala SS, often configured as a lowrider, a popular subject among early-90's gangsta rap.es:Sesenta y cuatro