Hello Sir, thank you for the educational videos! I'm new to celestial navigation and I have a question, if you don't mind. I did some sightings and checked the values in my nautical almanc, year 2023. For October 03, I can find a value for d = -1 at the bottom of the table of the daily pages. Now, the declination for e. g. 09:00:00 GMT lists S03°55.2'. For 10:00:00 GMT I can read S03°56.2'. So actually, the numbers are getting bigger from hour to hour. Since the trend is positiv, please correct me if I'm wrong, the correction should be added. If my understanding is correct, do you have an explanation, why in the almanc from 2022, as well as in the almanac of 2023, the d value is defined as d = -1? Is it correct to follow the trend? I'm using a free online version for exercise purpose. I would really appreciate if you could help me. Thanks in advance!
The "d" at the bottom of the page does not have a sign, so I am not sure where you are coming up with a negative sign. The sign is determined by the trend of Declination over the day and specific hours that one is concerned with (always read the trend at the time of your sight as it can change during the day). As you correctly indicate above, in this case the trend of Dec is positive since the Dec values increase hour to hour, so the sign of "d" is positive.
This seems to be a bit advanced for me at present but . . . I want to know IF it is possible to determine longitude by any other method than knowing GMT. Since the earth and stars had been charted at least since writing numbers began, I think there must be a method. Surely whoever first charted the primary star locations must have researched and calculated how much angles varied between key stars as their navigators moved east or west across the earth. I understand the sun appears to move 15° every hour so our 24 hour days equals a 360° circle. Has the technique for star navigation been lost? I think you’re explaining how to find longitude from Greenwich but with out knowing GMT is there a way to locate yourself on the earth? Your explanation may be more than I can understand but please, point me in the correct direction. Because I’m interested in History and Archeology I think the people who built the Sphinx, pyramids and ziggurats around the World must have mapped their locations carefully. Otherwise, why did they spend so much time tracking every celestial movement? Thank you.
I am not an expert in “ancient” methods used for navigation so can’t address all of your question. But, finding longitude was difficult without accurate time which has been well chronicled in such books as “Longitude.” Unsatisfying answer probably but maybe someone can weigh in with other methods?
There was an excellent documentary on how the longitude problem was solved by John Harrison, an English carpenter who invented the first reliable marine watch. Before then there was no way to calculate longitude. It was this that lead to the exploration of the globe by Europeans. Prior to that sailors only had latitude as far as we know but did extremely well for all that.
You can use transit of known celestial phenomena to work out GMT (not sure about error though) - i.e Jupiter moon transist, or asteroids obscuring stars. Not something you would like to do on moving platform. For near bodies such as Moon your position on earth do matter.
I think you are referring to the first problem (time 11:34:28 GMT)? The d correction comes from the same minute box from which you grab the increments of GHA (in this case the 34 minute box), and yields a correction of +.3 for the d value of .5 pulled from the daily pages. The addition that you mention is due to the fact that you are adding a base 60 system (60 minutes to the hour), so when you add 1+4+3 in the 10's column for minutes you get 8 (or 80 minutes) which means you must carry over 1 whole hour (60 minutes) to the next column, leaving 20 minutes remaining. Make sense?
Quick question - shouldn't you flip the sign (positive to negative) when adding the correction to the GHA value? The trend is downwards, wouldn't that mean the 13 degrees is subtracted?
I'm assuming that you are referencing the two parts of the GHA calculation? The "hours" value (for the hour of the sight) and the "increments" value (for the minutes and seconds of the sight) are always added together. You want to capture the full GHA of the body at that specific time since the body continues to move in one direction (westward) over time. Subtracting one from the other would imply that the body (the sun in the example) had moved backwards during your sight. There may be additional corrections to GHA for some planets (to account for retrograde motion), which you will see described in the video on planets. Adding together the two segments of calculating GHA is different than the correction for Declination ("little d") which is a sign based on the trend of Dec from one hour to the next on the given day and varies throughout the year. Let me know if that is not clear!
Thanks 🙏 for lesson
Seems to cover everything and is so calm and nicely paced. I found this series really helped me too.
Hello Sir, thank you for the educational videos! I'm new to celestial navigation and I have a question, if you don't mind. I did some sightings and checked the values in my nautical almanc, year 2023. For October 03, I can find a value for d = -1 at the bottom of the table of the daily pages. Now, the declination for e. g. 09:00:00 GMT lists S03°55.2'. For 10:00:00 GMT I can read S03°56.2'. So actually, the numbers are getting bigger from hour to hour. Since the trend is positiv, please correct me if I'm wrong, the correction should be added. If my understanding is correct, do you have an explanation, why in the almanc from 2022, as well as in the almanac of 2023, the d value is defined as d = -1? Is it correct to follow the trend? I'm using a free online version for exercise purpose. I would really appreciate if you could help me. Thanks in advance!
The "d" at the bottom of the page does not have a sign, so I am not sure where you are coming up with a negative sign. The sign is determined by the trend of Declination over the day and specific hours that one is concerned with (always read the trend at the time of your sight as it can change during the day). As you correctly indicate above, in this case the trend of Dec is positive since the Dec values increase hour to hour, so the sign of "d" is positive.
This seems to be a bit advanced for me at present but . . . I want to know IF it is possible to determine longitude by any other method than knowing GMT. Since the earth and stars had been charted at least since writing numbers began, I think there must be a method. Surely whoever first charted the primary star locations must have researched and calculated how much angles varied between key stars as their navigators moved east or west across the earth.
I understand the sun appears to move 15° every hour so our 24 hour days equals a 360° circle. Has the technique for star navigation been lost? I think you’re explaining how to find longitude from Greenwich but with out knowing GMT is there a way to locate yourself on the earth? Your explanation may be more than I can understand but please, point me in the correct direction.
Because I’m interested in History and Archeology I think the people who built the Sphinx, pyramids and ziggurats around the World must have mapped their locations carefully. Otherwise, why did they spend so much time tracking every celestial movement?
Thank you.
I am not an expert in “ancient” methods used for navigation so can’t address all of your question. But, finding longitude was difficult without accurate time which has been well chronicled in such books as “Longitude.” Unsatisfying answer probably but maybe someone can weigh in with other methods?
There was an excellent documentary on how the longitude problem was solved by John Harrison, an English carpenter who invented the first reliable marine watch. Before then there was no way to calculate longitude. It was this that lead to the exploration of the globe by Europeans. Prior to that sailors only had latitude as far as we know but did extremely well for all that.
You can use transit of known celestial phenomena to work out GMT (not sure about error though) - i.e Jupiter moon transist, or asteroids obscuring stars. Not something you would like to do on moving platform. For near bodies such as Moon your position on earth do matter.
Did you actually find the "d" on the 35 minute (3) instead of 34 (2.9)? Also, lost you adding 1+4+3 to get 2? carry the 1 over 1+5+8 etc.
at time 16:08
I think you are referring to the first problem (time 11:34:28 GMT)? The d correction comes from the same minute box from which you grab the increments of GHA (in this case the 34 minute box), and yields a correction of +.3 for the d value of .5 pulled from the daily pages. The addition that you mention is due to the fact that you are adding a base 60 system (60 minutes to the hour), so when you add 1+4+3 in the 10's column for minutes you get 8 (or 80 minutes) which means you must carry over 1 whole hour (60 minutes) to the next column, leaving 20 minutes remaining. Make sense?
Quick question - shouldn't you flip the sign (positive to negative) when adding the correction to the GHA value? The trend is downwards, wouldn't that mean the 13 degrees is subtracted?
I'm assuming that you are referencing the two parts of the GHA calculation? The "hours" value (for the hour of the sight) and the "increments" value (for the minutes and seconds of the sight) are always added together. You want to capture the full GHA of the body at that specific time since the body continues to move in one direction (westward) over time. Subtracting one from the other would imply that the body (the sun in the example) had moved backwards during your sight. There may be additional corrections to GHA for some planets (to account for retrograde motion), which you will see described in the video on planets. Adding together the two segments of calculating GHA is different than the correction for Declination ("little d") which is a sign based on the trend of Dec from one hour to the next on the given day and varies throughout the year. Let me know if that is not clear!