A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2021 Feb 14, 14:01 -0800
The amplitude tables assume the observer is at the center of the Earth. With the Moon at 208,000 nautical miles away and the Earth having a radius of 3440 nautical miles then there is a parallax of almost 1° . Other bodies in the solar system don't have enough parallax to worry about when taking an amplitude. This is why the Moon's upper limb is observed on the horizon vs. the Sun's lower limb 2/3 of a solar diameter above the horizon. There is also refraction and dip involved. A star amplitude is observed a bit more than one solar diameter above the horizon when taking an amplitude to allow for an approximate combined refraction and dip correction.