A light-hour is a unit of length useful in astronomy, telecommunications, and relativistic physics. It is defined as the distance that light travels in free space in one hour (or 3600 light-seconds), and is equal to 0.79252849099999977.9252849099999979.2528490999999632.528490999999695.2849099999966712.8490999999630738.4909999996889384.9099999964237219.099999964237213×10 m. It is just over 7.1×10 miles and approximately 3.54×1012 feet.