Hour, a unit for measuring time, defined as either 1/24 of a day or 3600 seconds (60 minutes). Used alone, the word hour refers to clock time, a composite of mean solar time and atomic time. There are other types of hours, such as sidereal hours (9.83 seconds shorter than clock-time hours), but these are primarily of theoretical interest. Scientists, who are most concerned with precise time intervals, tend to use decimal fractions of the various types of days and multiples of seconds instead of hours. (Seconds and days are based on measurable physical phenomena; the hour is derived from seconds and days.)
You Might Also Like
So much about galaxies remains a mystery. We know what they're made of and that we live in one (the Milky Way), but we're not sure how they form and evolve.
You've heard of the big bang, of course, but do you have any idea as to what was happening during that massive flurry of activity billions of years ago?