Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 26-09-2016, 17:17   #1
Registered User

Join Date: Aug 2010
Location: sydney, australia
Boat: 38 roberts ketch
Posts: 975
Images: 3
Is There A Math Formula For Deriving Sun's GHA @ UT?

i"ve worked out how to use a common spreadsheet to convert degree inputs to radians and then apply the spherical trigonometric equations in order to derive computed altitude and azimuth. This means i dont need the huge sight reduction tables.
My question is; is there a mathematical formula for the sun's GHA @ UT or is this necessarily based on observation?
__________________

__________________
charliehows is online now   Reply With Quote
Old 26-09-2016, 17:37   #2
Registered User
 
El Pinguino's Avatar

Join Date: Aug 2013
Location: el campo
Boat: 39' Westerly Sealord
Posts: 3,321
Re: Is There A Math Formula For Deriving Sun's GHA @ UT?

Yes there is and it a shame you didn't ask this question before I left the campo last week... I'm away from my books now.

However... they can be found in this book and elsewhere.... Astro Navigation by Pocket Computer | Trade Me

Very simple they are to...
__________________

El Pinguino is online now   Reply With Quote
Old 26-09-2016, 17:47   #3
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 15,563
Re: Is There A Math Formula For Deriving Sun's GHA @ UT?

Yes. There is a formula from a number of factors. Google your friend.

Otherwise how do you think they make printed almanacs?

b.
__________________
barnakiel is online now   Reply With Quote
Old 26-09-2016, 18:36   #4
Registered User

Join Date: Aug 2010
Location: sydney, australia
Boat: 38 roberts ketch
Posts: 975
Images: 3
Re: Is There A Math Formula For Deriving Sun's GHA @ UT?

thx, I'll go see mr magoo(gle)
__________________
charliehows is online now   Reply With Quote
Old 26-09-2016, 19:06   #5
Registered User

Join Date: Oct 2010
Location: The boat - New Bern, NC, USA; Us - Kingsport, TN, USA
Boat: 1988 Pacific Seacraft 34
Posts: 327
Re: Is There A Math Formula For Deriving Sun's GHA @ UT?

Try Cruising World Magazine, March 1996, page 48. https://books.google.com/books?id=yJ...urdoch&f=false
__________________
wsmurdoch is offline   Reply With Quote
Old 26-09-2016, 20:26   #6
Registered User

Join Date: Apr 2007
Location: New England
Boat: lagoon 380 s2
Posts: 327
Re: Is There A Math Formula For Deriving Sun's GHA @ UT?

Quote:
Originally Posted by charliehows View Post
i"ve worked out how to use a common spreadsheet to convert degree inputs to radians and then apply the spherical trigonometric equations in order to derive computed altitude and azimuth. This means i dont need the huge sight reduction tables.
My question is; is there a mathematical formula for the sun's GHA @ UT or is this necessarily based on observation?
Would you be willing to post the formula, or upload the sheet?

Sent from my SM-G900V using Cruisers Sailing Forum mobile app
__________________
jbinbi is offline   Reply With Quote
Old 27-09-2016, 06:51   #7
Registered User

Join Date: Oct 2010
Location: The boat - New Bern, NC, USA; Us - Kingsport, TN, USA
Boat: 1988 Pacific Seacraft 34
Posts: 327
Re: Is There A Math Formula For Deriving Sun's GHA @ UT?

I put this together years and years ago. It has been a long while since I have used it. I am not sure that it makes the date to time calculation correctly after the year 2000, but you can try it. It is what is behind the Cruising World article I mentioned earlier.
Attached Files
File Type: xls SunSight.xls (31.0 KB, 53 views)
__________________
wsmurdoch is offline   Reply With Quote
Old 27-09-2016, 07:56   #8
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 15,563
Re: Is There A Math Formula For Deriving Sun's GHA @ UT?

The formulas are multifactor but for quick and dirty solutions (e.g. in survival navigation) you can consider declination as a sine function with period equal to a year and extremes at tropics. Easy with any calculator BUT you do have to memorise some sine values if you want to calculate ad hoc in the field, with ball pen and paper.

https://en.wikipedia.org/wiki/Position_of_the_Sun


GHA can similarly be calculated from a linear approximation. Your main corrective factor comes from equation of time:

https://en.wikipedia.org/wiki/Equation_of_time

I think this place explains things in a neat and not too complicated way:

Part 3: Calculating Solar Angles | ITACA

etc.

b.
__________________
barnakiel is online now   Reply With Quote
Old 27-09-2016, 13:15   #9
Registered User

Join Date: Aug 2009
Boat: Tayana 37
Posts: 40
Re: Is There A Math Formula For Deriving Sun's GHA @ UT?

Quote:
Originally Posted by charliehows View Post
i"
My question is; is there a mathematical formula for the sun's GHA @ UT or is this necessarily based on observation?
Do not reinvent the wheel!

You can buy the official Nautical Almanac, Nautical Publication Number: NP 314 The Nautical Almanac, which tabulates all material needed for astro.

You can download a free Nautical Almanac look alike from:

"The Online Nautical Almanac" which tabulates GHA and other essential data.

The site Navigator Software is a very useful and reliable source for astro navigation information.
__________________
kish is offline   Reply With Quote
Old 27-09-2016, 13:42   #10
Registered User
 
Adelie's Avatar

Join Date: Feb 2010
Location: El Ciudad del Mission San Diego de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 2,580
Re: Is There A Math Formula For Deriving Sun's GHA @ UT?

Post the question to the NavList folks: http://www.fer3.com/arc/


A house is but a boat so poorly built and so firmly run aground you would never try to refloat it.
__________________
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
SailboatData
Adelie is offline   Reply With Quote
Old 27-09-2016, 14:42   #11
Registered User

Join Date: Jun 2015
Location: New Zealand
Boat: Custom sailing catamaran
Posts: 80
Re: Is There A Math Formula For Deriving Sun's GHA @ UT?

All you need is the number called "the equation of time" for the day. Calculate Gha from the difference between the equation of time and your clock time.
Declination is almost the same at the same times of the year.
However Nories tables and the current nautical almanack gives everything you need to reduce sights. Including trig tables for when your calculator blows up.
__________________
KJThomas is offline   Reply With Quote
Old 27-09-2016, 16:57   #12
Registered User

Join Date: Aug 2010
Location: sydney, australia
Boat: 38 roberts ketch
Posts: 975
Images: 3
Re: Is There A Math Formula For Deriving Sun's GHA @ UT?

My main reason for poking at this is the online sunsight reduction tool that I've been playing with doesnt have a downloadable version - bit annoying having to connect up just to do a bit of quick and dirty math, my version does pretty much the same, but the next obvious step is deriving GHA, LHA dec. etc. I think i've found a reasonable formula that doesnt require delving into VSOP tables, which will be accurate enough. As for putting up a downloadable version - if i can make it effective and presentable i'll have a go but unfortunately i dont have a website i can park it at so may not happen. As for the almanac - of course i have them on my laptop also but a spreadsheet shifts the whole process into time overdrive - the business of crawling through the huge ho229 tables can be replaced by half a dozen cells of formulae and executed in no time.
__________________
charliehows is online now   Reply With Quote
Old 27-09-2016, 17:11   #13
Senior Cruiser
 
StuM's Avatar

Cruisers Forum Supporter

Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43
Posts: 5,024
Re: Is There A Math Formula For Deriving Sun's GHA @ UT?

You may find some useful information here:
Computing planetary positions
__________________
StuM is online now   Reply With Quote
Old 27-09-2016, 17:43   #14
Senior Cruiser
 
StuM's Avatar

Cruisers Forum Supporter

Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43
Posts: 5,024
Re: Is There A Math Formula For Deriving Sun's GHA @ UT?

I think you may find the Excel formulas you need in this NOAA spreadsheet:

http://www.esrl.noaa.gov/gmd/grad/so...ations_day.xls

Details here: ESRL Global Monitoring Division - Global Radiation Group
__________________
StuM is online now   Reply With Quote
Old 27-09-2016, 17:52   #15
Registered User

Join Date: Apr 2007
Location: New England
Boat: lagoon 380 s2
Posts: 327
Re: Is There A Math Formula For Deriving Sun's GHA @ UT?

Quote:
Originally Posted by charliehows View Post
but a spreadsheet shifts the whole process into time overdrive - the business of crawling through the huge ho229 tables can be replaced by half a dozen cells of formulae and executed in no time.
+ Million!!!! couldn't have said it better than this.
__________________

__________________
jbinbi is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
"v" corrections GHA Mike1956 Navigation 19 15-01-2016 06:50
GHA Aries long term Table? PDA1 Navigation 11 18-12-2014 08:20
Is There a Formula for Determining Wetted Surface Area ? fstbttms General Sailing Forum 6 11-03-2012 13:38
Length Lost to Splicing - Is there a Formula ? SailFastTri Construction, Maintenance & Refit 1 02-01-2011 23:38
Is there a formula for Converting Compression Ratios Chief Engineer Engines and Propulsion Systems 8 01-06-2008 05:38


Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 16:32.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.