by alter-ego » Sun Nov 06, 2022 5:22 am
Chris Peterson wrote: ↑Sun Nov 06, 2022 4:22 am
alter-ego wrote: ↑Sun Nov 06, 2022 4:18 am
johnnydeep wrote: ↑Sat Nov 05, 2022 7:43 pm
I guess I was thinking that at the poles, the stars paths are circles around the poles, so why wouldn't the moon's path look similar? Plus, this pic apparently shows the moon's progress over 1.5 hours, which is 16th of the total 24 hour path, so why doesn't it show a slight curve? (Of course, the moon is also orbiting the earth at 12.5 degrees per day, but over 16th of a day that wouldn't affect the apparent path much.)
Without any disagreement wrt all the posts here, I want to comment on this composite.
FYI, for all practical purposes the correct 50° nominally parallel path (in azimuth) is displayed with maximum eclipse correctly positioned against the stars. However, there's one minor fault in the lunar path detail. Over the course of the composite image, the true lunar altitude changes by ≈ +0.7°(higher altitude,) because of the (more southerly) change in declination (~-12arcmin/hour). Interestingly, with close inspection, the composite image path shows a decrease (not increase) in altitude by close to the same factor. It could be there was a minus sign error in generating the lunar path, or just a coincidence (pretty common in my experience
)
How are you measuring that?
Yeah, good question. You just beat me to a correction edit I was going to make.
I made the assumption that the horizon is parallel to the long axis of the image, which is not necessarily correct, so I cannot claim that path error. In fact, the visible ground is sloped such that the lunar path yields a (more correct) positive altitude. However, I believe the local horizon can be deduced from the image, and I won't be surprised if there is no conclusive lunar path error. I enjoy these kinds of problems, so will pursue this to see where it goes.
[quote="Chris Peterson" post_id=326980 time=1667708570 user_id=117706]
[quote=alter-ego post_id=326979 time=1667708294 user_id=125299]
[quote=johnnydeep post_id=326968 time=1667677428 user_id=132061]
I guess I was thinking that at the poles, the stars paths are circles around the poles, so why wouldn't the moon's path look similar? Plus, this pic apparently shows the moon's progress over 1.5 hours, which is 16th of the total 24 hour path, so why doesn't it show a slight curve? (Of course, the moon is also orbiting the earth at 12.5 degrees per day, but over 16th of a day that wouldn't affect the apparent path much.)
[/quote]
Without any disagreement wrt all the posts here, I want to comment on this composite.
FYI, for all practical purposes the correct 50° nominally parallel path (in azimuth) is displayed with maximum eclipse correctly positioned against the stars. However, there's one minor fault in the lunar path detail. Over the course of the composite image, the true lunar altitude changes by ≈ +0.7°(higher altitude,) because of the (more southerly) change in declination (~-12arcmin/hour). Interestingly, with close inspection, the composite image path shows a decrease (not increase) in altitude by close to the same factor. It could be there was a minus sign error in generating the lunar path, or just a coincidence (pretty common in my experience :))
[/quote]
How are you measuring that?
[/quote]
Yeah, good question. You just beat me to a correction edit I was going to make.
I made the assumption that the horizon is parallel to the long axis of the image, which is not necessarily correct, so I cannot claim that path error. In fact, the visible ground is sloped such that the lunar path yields a (more correct) positive altitude. However, I believe the local horizon can be deduced from the image, and I won't be surprised if there is no conclusive lunar path error. I enjoy these kinds of problems, so will pursue this to see where it goes.