# Why isn't Amplitude the same as Declination?

From the way I understand Amplitude and Declination, it seems to me that they should always be the same, yet they are not, why?

P.S. In the picture I am imagining that the declination remains constant (25 degrees N)

• What do you mean by 'amplitude' in this context? Commented Oct 8, 2022 at 12:31
• Yes, it's definitely with respect to the rational horizon cultofsea.com/navigation/amplitude Commented Oct 8, 2022 at 12:48
• @Harbard Feel free to write your own answer. This site could do with more celestial navigation content... Commented Oct 8, 2022 at 16:12
• @PM2Ring: It seems "celestial navigation content..." uses different vocabulary than standard observational astronomy, so maybe some sort of translation almanach first would be in place... Commented Mar 17, 2023 at 0:34

## 2 Answers

My original perception of the Declination was wrong, that's why I was confusing Declination with Amplitude.

Here's a correct way to imagine Declination and Amplitude. And in this picture you can also see why they're NOT the same.

An easy way to see this is to note that the "Amplitude" (the azimuth of a body when it is on the horizon) will depend on both the position of the body in the sky (the declination) and the position of the observer on the ground (the observer's latitude).

In particular $$\sin(\delta) = \cos(\lambda)\sin(A)$$ where $$\delta,\ \lambda,\ A$$ are declination, latitude and Amplitude resp.

So A isn't the same as declination.