Fatto generale: 30 is the duration in years of the Thirty Years' War - 1618 to 1648.
Fatto matematico: 30 is the largest number with the property that all smaller numbers relatively prime to it are prime.
Trivia: 30 is the number of days in the months April, June, September and November (and in unusual circumstances February).
Data storica: January 30th is the day in 1971 that Carole King's Tapestry album is released, it would become the longest charting album by a female solo artist and sell 24 million copies worldwide.