A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2016 Jul 26, 14:47 -0400
The direct answer to your question is that you should eliminate the dip correction when using a bubble "horizon".
When you use a natural sea horizon, the angle you measure is larger than the angular altitude of the object. What you want is the angle from a horizontal line to the line from your eye to the celestial object. When using the natural horizon, you also add in the angle between the horizontal line and the line from your eye to the natural horizon. That is the dip and what the dip correction does is eliminate that portion of the measurement.
When using a bubble "horizon", the angle downwards to the horizon from your eye is eliminated. There is no dip, and therefore, no dip correction.
BTW If the question was asked before, you didn't ask it! So no need to apologize!
Quick question regarding use of Celestaire practice bubble. Purchased one of these to practice with due to the lack of a readily available shoreline. In the Nautical Almanac, in the table for moon altitude corrections, noticed a small paragraph in the lower right, stating that if you use a bubble horizon, you should neglect the dip correction and subtract 15' for your reading. My queston is,would this apply to this particular practice bubble horizon, or is this for a more sophisticated bubble type horizon. Apologies if this question has been asked before. thanks!