Episode 3 of 3

Greenwich meridian as longitude reference

When: 1767
Where: Royal Observatory, Greenwich
Part of: Publication of the First Nautical Almanac

Because almanac observations were made at the Royal Observatory, Greenwich, the Greenwich meridian became the longitude reference for the Royal Navy and Admiralty charts.

Since the observations that fed into the Nautical Almanac were made at the Royal Observatory, Greenwich, the Greenwich meridian became the reference for measurements of longitude in the Royal Navy and on British Admiralty charts. The issues for 1767 to 1833 gave their ephemeris tabulations in terms of Greenwich apparent, rather than mean, time, anchoring the almanac's data to the Greenwich meridian from its first volume.

Sources

Nevil Maskelyne Wikipedia, revision of 2026-08-29
The Nautical Almanac Wikipedia, revision of 2026-06-18

Machine-drafted from the cited Wikipedia passages and checked by a reviewing model, not by a human editor. Every passage cites the revision it was written from; dates and places follow those passages.