# What does the "Mean" mean in GMT?

Asked by Trillian (21141) January 6th, 2010

In math, the “mean” is the average. What is the “mean” in Greenwich Mean Time? Just curious.

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Greenwich Mean Time is a term originally referring to mean solar time ” – wiki

occupying a position about midway between extremes http://www.merriam-webster.com/dictionary/mean

Thanks @uberbatman. I’m in math class right now and we were going over mean, median and mode. i knew that mean was average, and that the “M” was mean in the abbreviation. I just wondered if it were a different type of mean, or some archaic term.

Trillian (21141)

I think what it means (no pun intended) from a very technical point of view (though this may not be an exact definition) is that “mean” time is opposed to sidereal time. For example, a sidereal day is not “exactly” 24 hours, and “sidereal” Noon would vary from “mean” Noon in the same time zone because in a sidereal timing system “Noon” would be when the Sun is directly overhead—regardless of what the clock says.

So “mean” time groups a geographic band of varying longitudes (based on geographic features of Earth and political boundaries) and groups them together in a “Mean” timing system, so that we can set clocks similarly in various places and work by this collectively agreed-upon “mean” time.

For a more extreme example, China, as large as it is, is contained in a single time zone. So “noon” (meaning 12:00 PM by the clock) may be sometime in the afternoon in Shanghai (by a westerner’s “feeling” of what time it should be), and mid-morning in western China (by the same reckoning).

If this makes any sense…

CyanoticWasp (20271)

It means the people in Greenwich feel that they are not inclined to give their money to government, who in turn promises to give it to the poor in order to get votes and enslave the poor, so therefore the people in Greenwich are “mean”.

saint (3975)

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