73 (number) - Definition and Overview

73 is the natural number following 72 and preceding 74.

In mathematics

Seventy-three is the 21st prime number. The previous is seventy-one, with which it comprises a twin prime. It is also a permutable prime with thirty-seven. 73 is a star number.

Every positive integer is the sum of at most 73 sixth powers (see Waring's problem).

In science

• The atomic number of tantalium

In astronomy,

Messier object M73, a magnitude 9.0 apparent open cluster in the constellation Aquarius

The New General Catalogue object (http://www.ngcic.org/) NGC 73, 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 -716 July 16 and ended on 582 September 3. The duration of Saros series 73 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 -378 May 16 and ended on 902 June 23. The duration of Saros series 73 was 1280.1 years, and it contained 72 lunar eclipses.

In other fields

Seventy-three is also:

• The total number of books in the Holy Bible in the Catholic version if the Book of Lamentations is counted as a book separate from the Book of Jeremiah.
• The designation of USA Interstate 73, a freeway in North Carolina.
• The registry of the U.S. Navy's nuclear aircraft carrier USS George Washington (CVN-73), named after U.S. President George Washington.
• In baseball, the single-season home run record set by Barry Bonds in 2001.
• The year AD 73, 73 BC, or 1973.
• Ham radio operators often use the number 73 as a way of saying aloha. This is because in morse code it forms a palindrome --... ...-- which has a very distinctive sound.