At 10:44 the GHA of Aries is erroneously indicated as the angle to the star ... somewhat confusing. However, nice presentation ... very thorough ... very organized. As an old, rusty navigator (gone soft by GPS), I'm enjoying your seminars very much ... it's the way we were. Thanks!
Andy, thank you for this excellent resource. Thanks to your excellent instruction I am starting to get the hang of celestial navigation. Do you take questions? I have a situation where no matter what I do the LHA comes out to 113. This is for Dubhe, a circumpolar star. Of course I can't use an LHA of 113 in the sight reduction tables. Here are the particulars. I am on Cape Cod on a beach looking north at a longitude of approximately 70 degrees. I can see Dubhe for sure. The date is 9/15/24 and the time is 23:37:00 GMT. I get a GHA of Aries of 349 40.1. When I add the 193 41.9 SHA of Dubhe I get a GHA of Dubhe of 183 22.2 (543 22.0 - 360). If I use an assumed longitude of 70 22.0 I get an LHA of 113. I can't see a math error? I was able to plot Alkaid, Alioth, Schedar, and Kochab with no trouble and they are all in the same general area? Can you help me understand where I've made my mistake? Is there some sort of problem with circumpolar stars? Many thanks.
Andy, I figured it out. I'll keep it brief here, but I did prepare a document for myself to document my findings and I'd be happy to share it with you. While I could see Duhbe, it was "underneath" Polaris and therefore in a SHA whose GP would be on the "other side of the planet". So to help me know what range of SHAs I should look for in the star table when preparing to start a session, and particularly if I was looking north, I came up with the following formula. 360 - GHA Aries + Assumed Longitude = Middle of SHA ranges that will result in GPs that have LHAs that can be plotted. Middle of Range -/+ 90 gives easternmost and westernmost SHA that will result in GPs that have LHAs that can be plotted Example: GHA Aries = 350 Assumed Longitude = 70 360 - 350 + 70 = 80 80 - 90 = 350 SHA 80 + 90 = 170 SHA SHA range is 350 to 170
Hi Andy, great videos on celestial navigation - many thanks! One quick question: When shooting stars, I have pre-calculated the height and Zn for the star sights, normally for the time corresponding to the start of the respective twilight. When I shoot 3-5 stars, the actual time of shooting will differ by a few seconds or minutes (both from the pre-calculation time as well as between the stars individually). I would then calculate everything using the Nautical Almanac and the Sight Reduction Tables (similar to a sun sight). My question: would I have to calculate the LHA of the star for each star sight separately for its exact time? Or do I use the GHA of Aries for the pre-calculated time of twilight and just add the individual SHAs and transform to LHA - disregarding that each sight has its individual time stamp (which is a few seconds or minutes later than my pre-calculated time). Not sure I have to worry about this inaccuracy? Many thanks! Christian
Christian, Best practice is to always treat each sight as its own calculation. Precalculations are really just best guesses. It might not seem like a few seconds will make a difference, but in many cases they do.....there are no shortcuts!
Hello First of all thanks for your good job You are very good teacher. I have a question problem to you, I try to pre calculate the times of nautical and civil twilight, but I failed in some step, could you resolved this for me? My DR 39.09.00N, 009.25.00 W, I tried to prepare the sky with star finder 2102-D. Could you send me the results for the 12 of August 2023,thanks
First, apologies for my delayed response! Here is what I come up with. I'd be happy to show more details, but didn't want to take up the space in this message block. If you need to see the work, pass along your email and I'll send to you. Morning Nautical Twilight: 04:43 GMT Evening Civil Twilight: 20:06 GMT
At 10:44 the GHA of Aries is erroneously indicated as the angle to the star ... somewhat confusing. However, nice presentation ... very thorough ... very organized. As an old, rusty navigator (gone soft by GPS), I'm enjoying your seminars very much ... it's the way we were. Thanks!
Yeah, I noticed that too.
Andy, thank you for this excellent resource. Thanks to your excellent instruction I am starting to get the hang of celestial navigation. Do you take questions? I have a situation where no matter what I do the LHA comes out to 113. This is for Dubhe, a circumpolar star. Of course I can't use an LHA of 113 in the sight reduction tables. Here are the particulars. I am on Cape Cod on a beach looking north at a longitude of approximately 70 degrees. I can see Dubhe for sure. The date is 9/15/24 and the time is 23:37:00 GMT. I get a GHA of Aries of 349 40.1. When I add the 193 41.9 SHA of Dubhe I get a GHA of Dubhe of 183 22.2 (543 22.0 - 360). If I use an assumed longitude of 70 22.0 I get an LHA of 113. I can't see a math error? I was able to plot Alkaid, Alioth, Schedar, and Kochab with no trouble and they are all in the same general area? Can you help me understand where I've made my mistake? Is there some sort of problem with circumpolar stars? Many thanks.
Andy, I figured it out. I'll keep it brief here, but I did prepare a document for myself to document my findings and I'd be happy to share it with you. While I could see Duhbe, it was "underneath" Polaris and therefore in a SHA whose GP would be on the "other side of the planet". So to help me know what range of SHAs I should look for in the star table when preparing to start a session, and particularly if I was looking north, I came up with the following formula.
360 - GHA Aries + Assumed Longitude = Middle of SHA ranges that will result in GPs that have LHAs that can be plotted.
Middle of Range -/+ 90 gives easternmost and westernmost SHA that will result in GPs that have LHAs that can be plotted
Example:
GHA Aries = 350
Assumed Longitude = 70
360 - 350 + 70 = 80
80 - 90 = 350 SHA
80 + 90 = 170 SHA
SHA range is 350 to 170
Andy, I think the Lat for the DR should be changed to N instead of S to fit your homework solution. What do you think?
Yes, I've made the correction...transcription error I guess! Thanks for keeping me honest!
Well explained. Thanks!
Hi Andy,
great videos on celestial navigation - many thanks!
One quick question: When shooting stars, I have pre-calculated the height and Zn for the star sights, normally for the time corresponding to the start of the respective twilight. When I shoot 3-5 stars, the actual time of shooting will differ by a few seconds or minutes (both from the pre-calculation time as well as between the stars individually). I would then calculate everything using the Nautical Almanac and the Sight Reduction Tables (similar to a sun sight). My question: would I have to calculate the LHA of the star for each star sight separately for its exact time? Or do I use the GHA of Aries for the pre-calculated time of twilight and just add the individual SHAs and transform to LHA - disregarding that each sight has its individual time stamp (which is a few seconds or minutes later than my pre-calculated time). Not sure I have to worry about this inaccuracy?
Many thanks!
Christian
Christian, Best practice is to always treat each sight as its own calculation. Precalculations are really just best guesses. It might not seem like a few seconds will make a difference, but in many cases they do.....there are no shortcuts!
Andy,
It seems odd to be able to add a latidued and longitude for time. Could you expand on how that is done?
Thank you
Mike
Mike, Sorry for the long delay in responding. I am not sure what you are referencing, could you point it out? Thanks.
Hello
First of all thanks for your good job
You are very good teacher.
I have a question problem to you, I try to pre calculate the times of nautical and civil twilight, but I failed in some step, could you resolved this for me?
My DR 39.09.00N, 009.25.00 W, I tried to prepare the sky with star finder 2102-D.
Could you send me the results for the 12 of August 2023,thanks
First, apologies for my delayed response! Here is what I come up with. I'd be happy to show more details, but didn't want to take up the space in this message block. If you need to see the work, pass along your email and I'll send to you.
Morning Nautical Twilight: 04:43 GMT
Evening Civil Twilight: 20:06 GMT
Andy, after the Lat correction in homework 1 the intercept should be changed to Towards, what do you think?
Yes, that is correct. I had corrected some other errors but missed typing that in. Thanks for noticing!
Better explanation than indians