General fact: 28 is the number of Chinese constellations, "Xiu" or "mansions" (a literal translation), equivalent to the 12 western zodiac constellations.
Mathematical fact: 28 is a harmonic divisor number, a happy number, a triangular number, a hexagonal number, and a centered nonagonal number.
Trivia: 28 is the number of days in the shortest month of the Gregorian calendar, February (except in leap years, when there are twenty-nine).
Historical date: January 28th is the day in 1855 that a locomotive, on the Panama Railway, runs from the Atlantic Ocean to the Pacific Ocean for the first time.