General fact: 273 is the zero of the Celsius temperature scale (to the nearest whole number) in Kelvin.
Mathematical fact: 273 is an unremarkable number.
Trivia: 273 is the death toll of the air crash of American Airlines Flight 191.
Historical date: September 29th is the day in 61 BC that Pompey the Great celebrates his third triumph for victories over the pirates and the end of the Mithridatic Wars on his 45th birthday.