From https://www.apparent-wind.com/gmt-explained.html
Prior to 1925, astronomers reckoned mean solar time from noon so that when the mean sun was on the meridian, it was actually 00:00 GMT. This practice arose so that astronomers wouldn't have a change in date during a night's observing. Some in the astronomical community still use the pre-1925 definition of GMT in the analysis of old data although it is recommended that the term Greenwich Mean Astronomical Time now be used to refer to time reckoned from noon.

In reply to Re^5: Question regarding Time::Piece and timezones by jszinger
in thread Question regarding Time::Piece and timezones by atcroft

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