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 in the Padovan sequence, preceded by the terms 12, 16, 21 (it is the sum of the first two of these).
Trivia: 28 is the number of a car formerly run in the NASCAR Sprint Cup Series by Yates Racing.
Historical date: January 28th is the day in 1980 that USCGC Blackthorn collides with the tanker Capricorn while leaving Tampa Florida and capsizes killing 23 Coast Guard crewmembers.