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Re: An azimuth nomogram: what's under the hood?
From: Bruce J. Pennino
Date: 2018 Mar 13, 10:09 -0400
Hello:

This nomograph is very interesting.  I’ve done this calculation before never recognizing that it was a parabola .Here in New England (where we are having our third Nor’easter  in 11 days) many of us buy “Eldridge”.  Eldridge has a handy – dandy table in the back where for a specific date and latitude the  azimuth of sunrise and sunset is quickly obtained. I recollect that Mixter also has a similar table.  When it really matters, check you compass everyday.

Why is the declination of sun go to ninety degrees?  What have I missed?

The good news, this snow is light and fluffy, the last storm was shoveling 16 inches of wet mashed potatoes.

Regards,

Bruce

From: Tony Oz
Sent: Tuesday, March 13, 2018 8:45 AM
Subject: [NavList] Re: An azimuth nomogram: what's under the hood?

Dear Sean and Gary,

Thank you for the feedback.

I should have made the translation myself. The nomogram is called "A celestial body's rise and set semi-circular true azimuth".

The left wing of the parabola has the "Latitude of observer" label, the vertical scale has the "Declination of celestial body", the right parabola's wind has the "Rise (set) azimuth if same-name φ and δ" label on the inner side and the "Rise (set) azimuth if contrary-name φ and δ" label on the outer side.

The comment below the nomogram is "When observing from the sea level - the center of the celestial body is on the plane of horizon if: - Sun's lower limb is over the horizon at 0,7 of its diameter; - Moon's upper limb is at altitude ~0°; a star or a planet is at 0,5° altitude (a Sun's diameter)".

The rest of the text is translated correctly.

So, back to my initial questions.

I wonder why the nomogram is based on the parabola?

I wonder how could I re-calculate positions of each and every angular mark along each scale?

Regards,

Tony

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