Mountain time and Pacific time refer to two time zones located in the United States and Canada. Time zones are ranges of longitudes where a common standard time zone is used to account for the differing amounts of sunlight the regions receive over the course of a day.
The Mountain time zone is one hour ahead of the Pacific time zone, so when it is 8 a.m. in the Mountain time zone, it is 7 a.m. in the Pacific time zone.
The Mountain time zone starts in the western portion of the Great Plains states and includes all of Colorado, New Mexico, Wyoming, Montana, Arizona and Utah, and parts of Idaho. The Pacific time zone starts at the western boundary of the Mountain time zone and runs to the western coast of the United States and Canada. All of these states, except most of Arizona, observe daylight-saving time from mid-March into early November.
Times zones were created in 1884 at the Meridian Conference held in Washington, D.C. Each time zone is about 15 degrees of longitude wide, so there are 24 time zones around the world.
The amount of sunlight varies as the earth rotates, so different parts of the world face the sun, experiencing day, while others face away and experience night. Time zones take the rotation into account, so each region experiences daylight during approximately the same clock time each day.
Time zones are based off Greenwich Mean Time, which is the time in Greenwich, England, where the Prime Meridian passes through. Mountain Standard Time is seven hours earlier than Greenwich Mean Time and Pacific Standard Time is eight hours earlier.