A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Steve E. Bryant
Date: 2020 Feb 12, 19:06 +0000
My question is regarding the sun’s analemma.
The only thing I can say about the picture is that it is a demonstration of the 23ᵒ tilt of the earth’s axes against the background of space as the earth orbits the sun in the course of one year.
And then there is the notion of the “equation” of time for which I haven’t any appreciation.
So, my questions are these:
- I would like to see this same analemma only with some means of indicating where the equatorial horizon is with respect to each of the images of the sun.
- I am suspecting that there is no illustration as to where the celestial horizon would be with respect to the solar images except to imagine that it would be parallel to the equatorial horizon, not superimposed upon it but separated by an amount equal to the radius of the earth.
- Some additional explanation of the what the equation of time represents might help me to understand it. I’ve posted something I found online; even it is a little difficult for me to comprehend right now. I would like to be able to stop the motion of this GIF to compare the four graphic representations. The link below is a GIF which may or may not be visible as a part of my post but I’m certain you will be able to see it if posted on you own computer. https://upload.wikimedia.org/wikipedia/commons/1/12/EquationofTimeandAnalemma.gif .
Steve, OCBC, USPS
From: NavList@fer3.com <NavList@fer3.com> On Behalf Of
Sent: February 6, 2016 11:20 AM
Subject: [NavList] Re: Time of Sun & Moon rise and set
The rate of change in the sun's declination is illustrated by the Analemma (see attached). From 20 May to 21 July & from 22 November to 21 January the the sun's declination changes by approximately 1 degree per month. From 21 January to 20 May and from 23 July to 22 November the rate of change is approximately 10 degrees per month.