Reference photos for Eddington's Eclipse photos

[Gfamily]

i've been preparing a talk about Eddington and Crommelin's observations of the 1919 eclipse that demonstrated the deviation of star positions as predicted by Einstein's GR.
One thing that baffles me.
In the paper presented in November 1919, the details of the comparison images taken at Sobral were provided (page 12):

However, on July 10th, at 20:05 GMT, the eclipse field (which was in the constellation of Taurus) was about 50 degrees below the horizon.

Am I missing something?

[notFritzArgelander]

One needs to convert from GMT to local sidereal time to see "what's up"?

[Gfamily]

One needs to convert from GMT to local sideial time to see "what's up"?

Sort of; local sidereal time was just before 16h, and the target area is about 4h30 - so well below the horizon
I think it's easier to work on the basis that Sobral is only 3 hours behind GMT, which makes 20:05 GMT round about Sunset time, and the target area (around kappa Tauri) had set 2 1/2 hours beforehand.

I'd miscalculated the altitude in my OP; in fact, the target area was only 33 degrees below the horizon - but imaging the comparison plates would still be a problem.

It's possible that the comparison images were taken 12 hours earlier, at 08:05 GMT, (5am local time) but it seems surprising that such a basic error would have made it through.

[notFritzArgelander]

One needs to convert from GMT to local sideial time to see "what's up"?

Sort of; local sidereal time was just before 16h, and the target area is about 4h30 - so well below the horizon
I think it's easier to work on the basis that Sobral is only 3 hours behind GMT, which makes 20:05 GMT round about Sunset time, and the target area (around kappa Tauri) had set 2 1/2 hours beforehand.

I'd miscalculated the altitude in my OP; in fact, the target area was only 33 degrees below the horizon - but imaging the comparison plates would still be a problem.

It's possible that the comparison images were taken 12 hours earlier, at 08:05 GMT, (5am local time) but it seems surprising that such a basic error would have made it through.

Stranger things have happened. I do frequent teleconferencing with folks in NZ and even with the use of a scheduling app that should automatically account for time zone changes chaos frequently ensues.

[Gfamily]

One needs to convert from GMT to local sideial time to see "what's up"?

Sort of; local sidereal time was just before 16h, and the target area is about 4h30 - so well below the horizon
I think it's easier to work on the basis that Sobral is only 3 hours behind GMT, which makes 20:05 GMT round about Sunset time, and the target area (around kappa Tauri) had set 2 1/2 hours beforehand.

I'd miscalculated the altitude in my OP; in fact, the target area was only 33 degrees below the horizon - but imaging the comparison plates would still be a problem.

It's possible that the comparison images were taken 12 hours earlier, at 08:05 GMT, (5am local time) but it seems surprising that such a basic error would have made it through.

Aha! I see that the zero point for GMT changed in 1925 from Midday to Midnight - so the 1919 paper would have been based on the old definition


Who knew?

[notFritzArgelander]

One needs to convert from GMT to local sideial time to see "what's up"?

Sort of; local sidereal time was just before 16h, and the target area is about 4h30 - so well below the horizon
I think it's easier to work on the basis that Sobral is only 3 hours behind GMT, which makes 20:05 GMT round about Sunset time, and the target area (around kappa Tauri) had set 2 1/2 hours beforehand.

I'd miscalculated the altitude in my OP; in fact, the target area was only 33 degrees below the horizon - but imaging the comparison plates would still be a problem.

It's possible that the comparison images were taken 12 hours earlier, at 08:05 GMT, (5am local time) but it seems surprising that such a basic error would have made it through.

Aha! I see that the zero point for GMT changed in 1925 from Midday to Midnight - so the 1919 paper would have been based on the old definition


Who knew?

Well... I didn't for one. Nice catch.