NavList:

   

Reply

I would avoid mercury like the plague. It is very dangerous stuff -- even if
you can get it -- as it volatilizes at room temperature. Mercury vapours are
not something you want to inhale, even in small amounts. I suggest a pan of
waste oil. Something black and somewhat viscous. Only drawback: you get a
lot of detritus on the fluid and it is nearly impossible to clean. Down the
road, I would invest in a glass artificial horizon. I have been using one
for years and I love it. Only drawback: it must be perfectly level.

I had a few experiences similar to Gary. Once from my boat last summer and
once from the shore of beautiful Hall Beach. In the former case, I took a
round of sights off the water, and then switch to my bubble attachment.
Unfortunately, I cannot boast about the results. Still, it was fun.

Robert

----- Original Message -----
From: "GAry LaPook" 
To: 
Sent: Monday, January 22, 2007 6:38 PM
Subject: [NavList 2125] Re: First sights


>
> Gary LaPook wrote:
>
> You can also take sights using an artificial horizon.
> To make one of these simply put water in a saucer (or,
> much better if you can get it, use murcury) and the
> surface of the liquid will be perfectly horizontal.
> Measure the altitude of the star using its reflection
> in the saucer as the reference point instead of the
> horizon. Due to the geometry of the situation (angle
> of incidence equals angle of reflection) you end up
> measuring exactly twice the altitude. Then simply
> apply the index correction and divide the remainder by
> 2, then apply refraction but not dip corrections. You
> need a still night so that the wind doesn't ripple the
> surface of the water. I have been using a small bottle
> of murcury for over forty years for this and because
> of its reflective quality I can take second magnitude
> stars such as polaris, with water you can shoot first
> magnitude stars easily. If shooting the sun make sure
> you use both sets of shades and line up the lower limb
> with its reflection in the liquid which will be the
> top of the sun's reflection.
>
> I remember one night in 1990 we were anchored in a
> long fjord on the east coast of Tahaa (an island about
> 20 nm east of Bora Bora) and it was so still that I
> could see the stars reflected in the ocean around the
> boat. I got out my Tamaya and took a round of sight
> and got a fix that crossed on our anchorage.
>



--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply