NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: stange results from AM and PM sun shots
From: Bill B
Date: 2012 Sep 27, 19:54 -0400
From: Bill B
Date: 2012 Sep 27, 19:54 -0400
On 9/27/2012 12:47 PM, Alan S wrote: > I wonder is the above mentioned in just a peculiarity of late Sept. when > Sun's declination is so small, in some instances, less than 1D South. > Any ideas or light to be shed. Alan Keep in mind that what you see is not what you get. We are told with 0d declination the sun will rise and set due east and due west,and night and day will be equal lengths. This is not true for three reasons. 1. If the declination was 0d at LAN in September, the declination would be N at sunrise and S at sunset. 2.Even if declination was 0d at rise and set, that would be for the center of the sun, not the upper limb which we use to define rise and set. 3. Due to refraction, we are seeing a limb that is not there in a vacuum. The refraction correction would be -0d 33!8 for the center of the sun or upper limb on the horizon. Therefore it is quite possible to have an Hc north of 90d or 270d near the autumnal equinox. If memory serves there is about an 8 day lag past the equinox before light and dark are equal. To make matters more confusing, 0d declination does not exactly define the equinox as I recall. Somewhere in my archives there is an explanation and diagram posted by a list member perhaps 7 years ago. I'll try to locate locate that. In memory of George I'll mention that when I learned the above I was as disillusioned as a kid finding out his "sea monkeys" were nothing but brine shrimp. This caused George to rebuff me as he asserted younger and foreign list members had no idea what I was talking about. To get those not in the know up to speed: http://en.wikipedia.org/wiki/Sea-Monkeys Bill B