Thirty is:
* The number of days in the months April, June, September and
November.
* The total number of major and minor keys in
Western tonal music, including enharmonic equivalents.
* The minimum age for United States senators.
* In years of marriage, the pearl wedding
anniversary.
* The duration in years of the Thirty Years' War - 1618 to
1648.
* The code for international direct dial phone
calls to Greece.
* The designation of Interstate 30, a freeway that runs from Texas
to Arkansas.
* The number of tracks on The Beatles'
eponymous album, usually known as The White Album.
* A stage in young adulthood.
* Judas Iscariot betrayed Jesus for 30 pieces
of silver. Matthew 26:15.
* The sum of the first four squares, which makes it a square
pyramidal number.