how to use artificial horizon with sextant?

[shamblin]

I can do the noon sun sight with my mk3 plastic sextant and would like to continue developing skills inland.  Would someone please explain just what one does with an artificial horizon as compared to using the ocean horizon?  Aparently there is the bubble horizon and a more horizontal dish variety? Or should I just order the Davis model and follow the book?  Thanks much.  Bill in NC 

[HenryC]

I've never used the "bubble" attachment, but I guess the instructions come with it when you buy it.  This is a type that attaches to your sextant, as opposed to a "bubble sextant" which is used in aircraft navigation and not suitable for a boat which is always in motion.

An "artificial horizon" is nothing but a pan filled with a dark, reflecting liquid (like motor oil, although in the old days they used mercury) protected from rippling in the wind by a hood. You set it on the ground and the surface of the liquid becomes a perfectly flat horizontal plane.  Instead of aiming the horizon glass of the sextant at the horizon, you aim it at the reflection of the sun on the liquid, and then you shoot your sight as usual.  Because of the multiple reflections, you have to multiply your readings by 2 or by 1/2, I forget which.

I would suggest you save your money and just practice by using a flat object, like a rooftop, gable, or telephone line as your horizon to learn how to manipulate the sextant and take readings.  The readings will be meaningless, of course, but you'll get your practice that way and become familiar with handling your instrument and getting consistent readings..  When you're ready for a real sight, drive to the ocean or to a big lake with an opposite shore over the horizon.

For more about bubble sextants, read this:

http://www.qmss.com/seastories/seastory05.html

There are several other "sea stories" and "articles" about celestial on that website you might be interested in.  Also, check out my other posts on Celnav elsewhere on this site.

[shamblin]

OK, thanks. Maybe I get it.  Instead of seeing 1.the sun and 2.the horizon in the sextant and adjusting the sextant until those 2 images come together,  I see 1. the sun and 2. the reflected sun in the sextant and adjust until those images come together? 

[HenryC]

Correct.  Although I must confess I've never actually used an artificial horizon myself, because I've always lived just a few minutes drive drom the beach.