NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Winter solstice this weekend
From: Peter Hakel
Date: 2014 Dec 20, 01:24 +0000
From: Samuel L <NoReply_SamuelL@fer3.com>
To: pmh099@yahoo.com
Sent: Friday, December 19, 2014 12:36 PM
Subject: [NavList] Re: Winter solstice this weekend
From: Peter Hakel
Date: 2014 Dec 20, 01:24 +0000
Sam,
Depending on your level of patience, you could vary the input UT in the sun.xls spreadsheet until you reach the most negative declination. To gain extra precision you can unlock the spreadsheet and display sun’s Dec with additional decimal digits; in the attached screenshot I copied this value into the yellow cell E6 from B60. For illustration, I am showing more decimals in E6 than is reasonable but I wanted to see Dec changing with every second as a numerical experiment.
This website:
http://wwp.greenwichmeantime.com/longest-day/equinox-solstice-2010-2019.htm
says it’s 23h 03m
and my Excel says: 23h 02m 30s
which is close enough for navigation work. :-)
Finding equinoxes this way is easier, since the Dec rate of change is the fastest and all you need to watch for is the change in sign.
Peter Hakel
Depending on your level of patience, you could vary the input UT in the sun.xls spreadsheet until you reach the most negative declination. To gain extra precision you can unlock the spreadsheet and display sun’s Dec with additional decimal digits; in the attached screenshot I copied this value into the yellow cell E6 from B60. For illustration, I am showing more decimals in E6 than is reasonable but I wanted to see Dec changing with every second as a numerical experiment.
This website:
http://wwp.greenwichmeantime.com/longest-day/equinox-solstice-2010-2019.htm
says it’s 23h 03m
and my Excel says: 23h 02m 30s
which is close enough for navigation work. :-)
Finding equinoxes this way is easier, since the Dec rate of change is the fastest and all you need to watch for is the change in sign.
Peter Hakel
From: Samuel L <NoReply_SamuelL@fer3.com>
To: pmh099@yahoo.com
Sent: Friday, December 19, 2014 12:36 PM
Subject: [NavList] Re: Winter solstice this weekend
I'm curious to know how the time of the Solstice is determined.
I found which hour the Sun dropped to S 23d 26.1min Declination- 12/21/14 at 16hrs GMT and then began the rise back North- 12/22/14 at 6hrs GMT.
The number of hours between those hours (14 hours) was divided by 2 and added (or subtracted) to one of the hours to obtain a time of 23:00:00 on 12/21/2014.
Using Peter Hakel's, sun.xls spreadsheet I also established GHA at 180d on the same date thinking that might be reference point and got GMT 23:58:16.5
Any ideas what to do?
Thanks,
Sam L.
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