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Re: USNO web app cloned
From: Frank Reed
Date: 2020 Sep 15, 18:56 -0700

Eric Fernandez, you wrote:
"It looks really nice! "

Glad you like my clone.

You also wrote:
"Sometimes the Sum of corrections does not match individual correction values, I suppose this is caused by rounding, although the internal precision is higher than 1/10th of [minute]."

Right. It's just rounding. 0.1+0.1 can add up to 0.1. How? If the first number is "really" 0.06 displayed as 0.1 by rounding and the second number is 0.07 also displayed as 0.1, the sum would be 0.13 which rounds down to 0.1. And so on...

You asked:
"One question about refraction correction: close to Hc=0 I get quite different value. They match starting from 5 to 10 degrees. Which formula did you use for it please?"

What formula (or class of formula) do you think we should be using? Let me remind you and everyone else reading along that I designed this USNO clone to be a nearly exact duplicate of the features of the original USNO app, including some small flaws. I did not design it to be a better mousetrap. If I am reading your question right, you may well have noticed one of those flaws or peculiarities. But is it really a flaw? That depends on the intended purpose of those numbers. The corrections are clearly not intended for reducing actual sextant sights. You wouldn't go to this app to work up a sight. So what are they for??  By the way, you can also question the values for the Moon's parallax in altitude. Do they make sense to you? A question for you and anyone else following along: if the Moon's HP is 56.5' (as an example), and we have calculated its altitude (Hc) as 45°00' exactly, then what is its parallax in altitude? Are there two options? Do they both make sense?

Frank Reed

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