[tz] Old London Meridian

Tim Jacobs tz at mitxela.com
Fri Jan 29 15:19:10 UTC 2021

Lines 106 to 125 of tz/europe mention the old meridian before Greenwich. 
The estimated position is 51° 28' 30" N, 0° 18' 45" W, which would put 
it north of the river in the grounds of Syon House.

The meridian markers are in fact all south of the river, and can be seen 
by walking the Thames Path on the south bank. The meridian passes 
through the King's Observatory, with obelisks to the north and south. 
The map on the information boards shows a total of four obelisks marking 
the meridian.

The website for the King's Observatory quotes the following: "This task 
was later transferred to Greenwich Observatory but not before three 
obelisks had been erected in the Old Deer Park in June 1778 to assist in 
the exact alignment of instruments in the Observatory. The northern one 
and the western one of the southern pair are on the true north-south 
meridian line passing through the west room of the Observatory which 
housed a tracking telescope. The southern obelisk is due south from the 
east room that at the time housed its great mural quadrant."

The position of the King's Observatory is given on Wikipedia as 
51°28′08″N 0°18′53″W, which would give STDOFF = -0:01:15.53

I don't suppose anyone is particularly concerned about this, but I 
thought I would point it out.

More information about the tz mailing list