Greenwich Observatory

Time keeping eventually advanced to the point where clocks needed to be synchronized with each other. Greenwich observatory eventually won out as that synchronization point.

Working Together

2 different astronomers working together on something happening in the skies needed to have their clocks synchronized to each other. As high noon changes continuously as the Earth rotates, the distance east/west between astronomers around the globe would upset their relative time.

Even when astronomers are using Mean Time they still have clocks that differ in indicated time based on the locations of their observatories.

To compare notes they needed to coordinate their clocks and report their scientific results in a time indicated on a reference clock.

Meridians track distance east and west around the globe. So the question of setting a reference clock is really a question of determining where meridian zero, or the Prime Meridian, should be located.

The final selected of a prime meridian was worked out at the Prime Meridian Conference held in Washington DC in October of 1884. In that conference the meridian and observatory were selected as The Royal Observatory Greenwich. The foundation stone for that observatory was laid on August 10, 1675.

You should see from this founding date was at a time of great scientific advancement in the areas of time keeping and geography.


That observatory still remains. Here is a video of a walking tour. You can see how the hill overlooks London, and you can see the various pieces of equipment in the facility.

Key Points

Picking this location was mostly a function of power politics.

That observatory sits on a hill above a naval collage. The reference to the naval collage is important. Not only did astronomers need coordinated clocks, so do did the military.

If you are going to plan a military battle to start at a given time, then you must have coordinated clocks. So the Royal Navy was important in sponsoring a centralized clock.

This location was used as the reference clock for the Royal Navy for about 200 years before it was adopted as the international standard.

Inspired Prime Meridian?

The modern Prime Meridian was set in part in 1884 because the British navy had charted most of the oceans and those charts were designed with their prime meridian at Greenwich. This was simply a practical consideration.

Does scripture have a different prime meridian? yes

Discussion of that is under the Theory tab. We will get to that problem soon enough.

If you have been following this series of articles you should note how important local noon is to setting ancient clocks.

Local noon can also be used for discovering location. Harnessing that fact demanded a clock more accurate and rugged than had ever been built before. We turn to that use of local noon next.