A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Steve E. Bryant
Date: 2019 Jun 11, 12:48 -0500
On Jun 11, 2019, at 12:02, John D. Howard <NoReply_Howard@fer3.com> wrote:
I cannot answer all your questions, only number 5.
a. Sea horizon is easy, as you said. It will require a Height of Eye above the water. HOE will then figure the dip.
b. Bubble is for us that use an aircraft sextant. Aircraft sextants use a bubble to determine the level - put the sun ( or star ) in the bubble. No HOE needed nor dip.
c. A mirror artificial horizon is used inland ( to practice ) with a marine sextant. The angle that the the sextant reads is twice the normal angle so the App will show twice the normal angle. No HOE or dip. The distance to the mirror does not matter.
d. True horizon is defined as 90 degrees to down. Some of us use a theodolite to measure the sun and stars. Any instrument that is leveled with a plumb bob or gravity uses the true horizon. No HOE or dip.
e. Geocentric measures the angle from the center of the earth, not the surface. The almanacs give the angles from the center of the earth. Does not matter for stars but for close-in bodies, primarly the Moon, the angle will be different measured from your position on the surface. This difference is called parallax.
Hope this helps.
John H. 41N 100W