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Re: Corrections for latitude when taking sights
From: David Pike
Date: 2019 Mar 13, 16:56 -0700

Brad you wrote:

I don't doubt for an instant that the object will be on the prime vertical, at some instant in time. That's intuitive.

The conundrum I am dealing with is the assertion that the object (sun) will be 90° in azimuth. That is the part I am having trouble with. If I am at any latitude greater than 24°, then the azimuth to the sun can never be 090 or 270. Unless I have lost my mind (* several people are typing *), you will have to look to the N from the S hemisphere and to the S in the N hemisphere. I will never look due east (90) or due west (270) from my position. What am I missing?

Brad.

It’s easy to get confused; well it is for me. Stop thinking about it for a moment, and come at it from a different angle.

Ignore the equation of time for the moment.
I live at 53N.
Where does the Sun rise? A. Roughly in the East. So what’s its azimuth? A. roughly 090.

When is the Suns azimuth to me really close to 090? A. 6.00AM. It has to be otherwise it can’t be azimuth 180 to me at noon

What’s the definition of my prime vertical? A. A great circle going through my zenith and points on my east and west horizon. Therefore the Sun has to cross my prime vertical when its azimuth to me is 090 (by definition).

At the equinoxes the Sun will cross my prime vertical at my horizon at roughly 6AM and 6PM for all sensible latitudes (check the daily pages for around 21^st March and 23^rd September). In the summer, it’ll be higher at 6AM and 6PM, but it’ll always be at azimuth 090 and 270 to me. DaveP

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