103 is the natural number following 102 and preceding 104.

In mathematics

One hundred three is the 27th prime number. The previous prime is 101, making them both twin primes. 103 is a strictly non-palindromic number, it is not palindromic in any base from base 2 to base 103.

In science

• The atomic number of lawrencium, an actinide.

In astronomy,

Messier object M103, a magnitude 7.0 open cluster in the constellation Cassiopeia

The New General Catalogue object NGC103 , an open cluster in the constellation Cassiopeia

Asteroid 103 Hera

The Saros number of the solar eclipse series which began on 387 April 4 and ended on 1667 May 22. The duration of Saros series 103 was 1280.1 years, and it contained 72 solar eclipses.

The Saros number of the lunar eclipse series which began on 454 August 24 and ended on 1951 February 21. The duration of Saros series 103 was 1496.5 years, and it contained 84 lunar eclipses.

In other fields

One hundred three is also:

• The flight number of Pan Am Flight 103, which crashed over Lockerbie, Scottland and was at one time called "the air-disaster of the century".
• The year AD 103 or 103 BC.