SailNet Community - View Single Post - practicing with sextant on land
View Single Post
post #4 of Old 04-25-2010
Senior Member
AdamLein's Avatar
Join Date: Nov 2007
Location: SF Bay area
Posts: 1,940
Thanks: 9
Thanked 7 Times in 6 Posts
Rep Power: 10
As you say, there is no dip correction when you're using an artificial horizon, as you are. Height of eye is only important for calculating dip correction.

You probably already know that the height of eye/dip correction comes from the fact that an ideal horizon is truly horizontal, whereas your real horizon at sea is somewhat (dipped) below an imaginary horizontal plane tangent to the Earth at your feet. So if you're measuring the angle from the apparent horizon to a star, it's the angle from the invisible true horizon to the star, plus the angle from the apparent horizon to the invisible true horizon. Hence the dip correction is always subtracted from a sight off the apparent horizon.

On the other hand, regardless of your altitude, the artificial horizon is parallel to the ideal horizon, which means that they meet at the horizon So they're really the same thing when you put it all into perspective.

Back to altitude, the difference is too small to create a parallax effect, which is the only other geometrical issue arising from changing your position on the Earth. One possible problem would be atmospheric refraction of low-altitude bodies, but only at very very low altitudes that you probably cannot get in your artificial horizon anyway.

I would not worry about your height of eye.

Your main problem is that the more you practice, the more frustrating it will be for you to be landlocked.

s/v Laelia - 1978 Pearson 365 ketch
AdamLein is offline  
Quote Share with Facebook
For the best viewing experience please update your browser to Google Chrome