The CalcTool Community Forum

Hi,

I would like to see a sight reduction calculation for
sun, moon and several starts. I currently do this
with sight reduction tables (Nautical Almanac, 2008
Commercial Edition- HM Nautical Almanac Office).
But it should be possible to create a JavaScript
using spherical geometry to run these calculations.posting.php?mode=post&f=3#

Hi Colobus, and thanks for your suggestion.
Is there any more information you can give us about the calculation you are interested in? For example, what would the inputs and outputs for the calculation be? I have to confess that I don't know anything about this subject, so I will need help. To be honest, I'm not even sure if this is for astronomy, sailing, or something else! Best of all would be if you could point me to a web page that outlines the calculations in question.
I hope you can help us to help you...

Hi,

Thanks for the response.

If you do a google search on the string "sun sight reduction"
you will come across many Web pages with leads on this.
Basically, you need your appromite position the exact angle reading
from the sextant on the celestial object (the sun) from the horizen
(this is what sextants do - check it out on wikipedia) and the exact
time of the observation. As I said in my post, I use "sight reduction tables".
Other things to compensate for are the hight above the sea, angle correction
for refraction when the sun is near the horizen, etc..

Again, thanks for the reply.
Colobus

P.S. Sextants, until the recent intoduction of GPS, were the only way to find
your position; particularly longitude. One was use by Lewis and Clark on their
exploration of the western U.S.. They have been the traditional means of finding
position at sea, where there are no way marks. They are still used at sea as a
back up (no batteries or power required), by old sailors (like me) and were once
routinely installed in B-52s ( I have one of those too.)

Hi Colobus.

Thanks for the information. I've looked into it a bit, but it looks pretty dizzying to make the calculations work over a reasonable period of time, due to the complexity of planetary motion as well as the additional factors that need to be taken into account. I think it would need some input from an expert in the field, either to lay down exactly how the calculation should work, or to provide some free-to-use javascript.
If you have any leads for that (or if you can contribute yourself), then that would be great. Otherwise, it will go on my "to-do" list, but it will likely be a good while before I can get my head around it.

Hi !
I've just visited this forum. Happy to get acquainted with you. Thanks.