I had to take a 3-week celestial course to get my license but it wasn’t until I watched your series that I fully understood what’s happening. The context and visuals you give provide a crystal clear overall picture of what is actually going on behind the calculations. Thank you
So up to minute 32:44. Following my last statement, If "d" is +60, the final Hc would be 45deg 34min, not 44deg 24min. Ho is 44deg 12min, so the intercept is 1deg 22min giving 82nm away. Am I following this correctly?
I agree with @cruepprich, these explanations are brilliant. They're enabling me to understand what I'm doing, not just trying to remember by heart. Thank you!
This was excellent. I've had a lot of fun learning to use 249 and refer back to the videos frequently for a refresher. I do have a question though and that is the tables limiting use of stars to those at low elevations. Is it accepted that many suitable stars might be beyond the scope of these marvellous tables? I have the British AP 3270 That Volume 1 "Selected Stars" and a lot of the preferred stars are higher in the sky than 20° What do practicing navigators do about this limitation or have I completely misunderstood it all Just in case I have bought a Commercial edition of 220 for my latitudes (mid 50s) and will try to learn that next. I think it won't be too hard as you have given us such a solid foundation.
249 Volume 1 tables (Selected Stars) are designed to provide stars that, when reduced and plotted, will result in the most accurate fix. That means generally no really low- or really high-altitude stars, and stars that will be found around the full horizon so a range of bearings can be used. It is a given that not all of these selected stars would necessarily be useable but it is a starting point for making a list of possible stars to shoot. A good practice would be to augment that list with several other stars (and planets) in case of clouds or other factors limit sights.
I lost track of comments so apologies for the delayed response. In case you haven't already figured it out, because the Latitude is South the formula is LHA less than 180, ZN=180+Z (formulae for S. Latitude is at the bottom left of each page). A reminder of how many ways there are for anyone (even experienced navigators) to make mistakes!
Not sure what you are referencing (hopefully I didn't misspeak in the video!). GHA and LHA are always measured to the West (from Greenwich and from your longitude, respectively). Longitude is measured E and W from Greenwich. The calculation for LHA either ads or subtracts an Assumed longitude from GHA. When you lay it out on a diagram it makes it more clear (refer to Episode 4 for that explanation).
@@thenavstation Thank you for the reply. It is really just a question about convention having to do with the direction for "positive" angles. As measured from Greenwich, the "positive" directions for GHA and Longitude are opposite (GHA west and Longitude east). Was just wondering what the reasoning for this is? Why wouldn't positive GHA and positive Longitude be measured in the same direction. Thank you for your efforts. These are marvelous lectures. Very informative.
"Hour angles" (GHA, LHA, SHA) are measured to the West through 360, so technically there is no + or - direction. Longitude is only designated E or W. The plus/minus construct is really only used in GPS or other systems where one must label coordinates to differentiate them which I assume was done for simplicity in entering arguments. That is different than the mathematical "formula" used to convert GHA and longitude to LHA which does mean either adding or subtracting your longitude from GHA. Best I can do for you!
The only modern tables that have a time limit is Vol 1 of 249 (Selected Stars) which are good for 5 years either side of a central year (the stated Epoch). The other tables (229 or 249, and many others) are just mathematical solutions with no expiration date.
Three reasons: 1) 249 is much easier and faster to use, 2) fewer volumes of 249 are required to cover all latitudes, 3) the 1-mile accuracy of 249 is sufficient for typical small boat navigation (vs. .25 mile accuracy of 229).
KOIK (known only if known). This is an academic lecture which cannot be used for any practical application. Consider a navigator's log. What from this could be put in his Excel sheet? Nothing. Could a teacher's aid test the student's learning? No. So, the only application is to pass the teacher's test, which, like most college classes, has no practical application. The next revision of this lecture should be a review of a navigator's log and the formulas in it (Excel file attached) and work back though the log. Not the other way around which, as I said, has no practical application. A redo is needed for a student to learn. Notice the lack of comments which equals the lack of watcher's interest/referral to others. This proves the lecture has no value and must be redone. The need to capture the teacher's knowledge is great, but this i NOT THE WAY to do it. Try it my way and see if it works.
Do spreadsheets work without electricity. ? Said the man to his crew mates as he leaps into his life raft "I have to go back for my laptop" Peals of laughter as the medic administers a sedative. I think every episode of this series is prefaced by the statement "Turn off your GPS ...." This course is an introduction to the practice 'ab initio' and if you have followed from the beginning you will have seen that the lecturer's stated goal is to get folk familiar with the basic processes of using the specified sight reduction and plotting system. What's more, it works!
I had to take a 3-week celestial course to get my license but it wasn’t until I watched your series that I fully understood what’s happening. The context and visuals you give provide a crystal clear overall picture of what is actually going on behind the calculations. Thank you
Such a good explanation. I like that you really make every word count. I re-watched several times to make sure I got all the details. Thanks!👍
Thank you so much. I enjoyed your lessons. Very clear instructions indeed.
So up to minute 32:44. Following my last statement, If "d" is +60, the final Hc would be 45deg 34min, not 44deg 24min. Ho is 44deg 12min, so the intercept is 1deg 22min giving 82nm away. Am I following this correctly?
Is it possible to use the sight reduction tables in the Nautical Almanac instead of HO 249?
Very helpful and a great pace. Thank u
Thanks Tony, glad you are enjoying it!
At minute 28:15 your three arrows show little d as +60. -60 is in the next row. Just thought you might like to know. And 179 is less than 180.
Yes, as noted above in the intro copy I made an error (but corrected it on the fly!)....didn't want to re-tape the episode. Apologies but it happens!
My Excel sheet agrees that 179 is less than 180. Thank you Peter for catching the errors. Note, no others noticed, cared, or even watched.
Great Instructor - Thank you much
I agree with @cruepprich, these explanations are brilliant. They're enabling me to understand what I'm doing, not just trying to remember by heart. Thank you!
Very well explained, thank you.
This was excellent. I've had a lot of fun learning to use 249 and refer back to the videos frequently for a refresher. I do have a question though and that is the tables limiting use of stars to those at low elevations. Is it accepted that many suitable stars might be beyond the scope of these marvellous tables?
I have the British AP 3270 That Volume 1 "Selected Stars" and a lot of the preferred stars are higher in the sky than 20°
What do practicing navigators do about this limitation or have I completely misunderstood it all
Just in case I have bought a Commercial edition of 220 for my latitudes (mid 50s) and will try to learn that next. I think it won't be too hard as you have given us such a solid foundation.
249 Volume 1 tables (Selected Stars) are designed to provide stars that, when reduced and plotted, will result in the most accurate fix. That means generally no really low- or really high-altitude stars, and stars that will be found around the full horizon so a range of bearings can be used. It is a given that not all of these selected stars would necessarily be useable but it is a starting point for making a list of possible stars to shoot. A good practice would be to augment that list with several other stars (and planets) in case of clouds or other factors limit sights.
Thank you so much for a really helpful response.
In Homework problem #2, I found Hc OK, but from the table Z was 94. 360-94=266°, not 274° as you have as the answer. What did I do wrong?
I lost track of comments so apologies for the delayed response. In case you haven't already figured it out, because the Latitude is South the formula is LHA less than 180, ZN=180+Z (formulae for S. Latitude is at the bottom left of each page). A reminder of how many ways there are for anyone (even experienced navigators) to make mistakes!
Why is the Greenwich (and local) hour angle measured positive to the west when longitude is measured positive to the east?
Not sure what you are referencing (hopefully I didn't misspeak in the video!). GHA and LHA are always measured to the West (from Greenwich and from your longitude, respectively). Longitude is measured E and W from Greenwich. The calculation for LHA either ads or subtracts an Assumed longitude from GHA. When you lay it out on a diagram it makes it more clear (refer to Episode 4 for that explanation).
@@thenavstation Thank you for the reply. It is really just a question about convention having to do with the direction for "positive" angles. As measured from Greenwich, the "positive" directions for GHA and Longitude are opposite (GHA west and Longitude east).
Was just wondering what the reasoning for this is? Why wouldn't positive GHA and positive Longitude be measured in the same direction.
Thank you for your efforts. These are marvelous lectures. Very informative.
"Hour angles" (GHA, LHA, SHA) are measured to the West through 360, so technically there is no + or - direction. Longitude is only designated E or W. The plus/minus construct is really only used in GPS or other systems where one must label coordinates to differentiate them which I assume was done for simplicity in entering arguments. That is different than the mathematical "formula" used to convert GHA and longitude to LHA which does mean either adding or subtracting your longitude from GHA. Best I can do for you!
@@thenavstation Thank you for the reply...I think I understand now.
Do sight reduction tables go out of date?
The only modern tables that have a time limit is Vol 1 of 249 (Selected Stars) which are good for 5 years either side of a central year (the stated Epoch). The other tables (229 or 249, and many others) are just mathematical solutions with no expiration date.
In minute 20:55 my tables reads +35 for d and not -35. Great it is correct at 25:23.
Why ho 249 rather than ho 229.?
Three reasons: 1) 249 is much easier and faster to use, 2) fewer volumes of 249 are required to cover all latitudes, 3) the 1-mile accuracy of 249 is sufficient for typical small boat navigation (vs. .25 mile accuracy of 229).
@@thenavstation Excellent. Thank you.
KOIK (known only if known). This is an academic lecture which cannot be used for any practical application. Consider a navigator's log. What from this could be put in his Excel sheet? Nothing. Could a teacher's aid test the student's learning? No. So, the only application is to pass the teacher's test, which, like most college classes, has no practical application. The next revision of this lecture should be a review of a navigator's log and the formulas in it (Excel file attached) and work back though the log. Not the other way around which, as I said, has no practical application. A redo is needed for a student to learn. Notice the lack of comments which equals the lack of watcher's interest/referral to others. This proves the lecture has no value and must be redone. The need to capture the teacher's knowledge is great, but this i NOT THE WAY to do it. Try it my way and see if it works.
Jerry, are you suggesting that the only way to effectively practice celestial at sea is by using formulae and spreadsheets? I respectfully disagree!
Do spreadsheets work without electricity. ? Said the man to his crew mates as he leaps into his life raft "I have to go back for my laptop" Peals of laughter as the medic administers a sedative.
I think every episode of this series is prefaced by the statement "Turn off your GPS ...." This course is an introduction to the practice 'ab initio' and if you have followed from the beginning you will have seen that the lecturer's stated goal is to get folk familiar with the basic processes of using the specified sight reduction and plotting system. What's more, it works!
If the Nav Station videos don't help you understand the sight reduction process you should find another hobby.