Time is always changing. Time never stands still. Time is continuous, and not stationary. Time changes our perceptions, and our perceptions of time change continuously. Time is infinite; change is essential to time.

A day is the duration of time it takes for the earth to rotate all the way around. The sun does not really move across the sky; it appears that way because the earth is spinning. A year is the time it takes the earth to orbit the sun.

Standard time is measured from the meridian of longitude that passes through the Greenwich Observatory in England. A meridian is an imaginary circle around the earth passing through the poles and any given point on the earth's surface. Longitude is a measurement of location east or west of the prime meridian.(the meridian that passes through both poles and Greenwich, England). Longitude is measured in degrees, minutes, and seconds. Greenwich Mean Time (GMT) is the mean solar time at the zero meridian of longitude.

There are 24 time zones. Each time zone is about 15 degrees of longitude in width (15 x 24 = 360). Within each zone, the local time is standardized. The time in each time zone differs from the time in the neighboring time zone by one hour. As you travel east, the time is one hour later in the next time zone. As you travel west, the time is one hour earlier in the next time zone.