55 (number) - Definition and Overview

55 is the natural number following 54 and preceding 56.

In mathematics

Fifty-five is a heptagonal number, a centered nonagonal number, and a triangular number, made up of the numbers 1 to 10 added up, and it is also the sum of the squares of the integers 1 to 5. It is also a Fibonacci number (the largest Fibonacci number to also be a triangular number) and a Kaprekar number.

In science

• The atomic number of caesium

In astronomy,

Messier object M55, a magnitude 7.0 globular cluster in the constellation Sagittarius

The New General Catalogue object (http://www.ngcic.org/) NGC 55, a magnitude 7.9 barred spiral galaxy in the constellation Sculptor

The Saros number (http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros1-175.html) of the solar eclipse series which began on -1255 July 6 and ended on 43 August 23. The duration of Saros series 55 was 1298.1 years, and it contained 73 solar eclipses.

The Saros number (http://sunearth.gsfc.nasa.gov/eclipse/LEsaros/LEsaros1-175.html) of the lunar eclipse series which began on -935 April 25 and ended on 345 June 1. The duration of Saros series 55 was 1280.1 years, and it contained 72 lunar eclipses.

In other fields

Fifty-five is also:

• The number of delegates who attended the Constitutional Convention.
• In gallons, a common size of drum containing liquids.
• In miles per hour in many states of the United States, a common speed limit; it was the national speed limit for a time during the energy crisis of the late 1970s.
• In years of marriage, the emerald wedding anniversary.
• The code for international direct dial phone calls to Brazil.
• The designation of United States Interstate 55, a freeway that runs from Louisiana to Illinois.
• The year AD 55, 55 BC, or 1955.