Fatto generale: 90 is the latitude of the North Pole and the South Pole.
Fatto matematico: 90 is divisible by the sum of its base 10 digits, thus it is a Harshad number.
Trivia: 90 is the number of minutes in a football (soccer) match.
Data storica: March 30th is the day in 1885 that the Battle for Kushka triggers the Panjdeh Incident which nearly gives rise to war between the British Empire and Russian Empire.