|I decided to revisit an idea that I had proposed last
January of using a liquid that would level itself and then turn into a
solid and I suggested using water for our northern brethren, see:|
I was just trying to think of what liquid I could use and I considered
glue or floor leveling compound but both are viscous so might not achieve
a perfectly level surface. Then yesterday suddenly it came to me, wax!
I went to a crafts store today and bought a pound and a half of candle
wax for $7.00 and a 7 inch round mirror for $3.00, total, ten bucks. I
filled a large pan with water, put the wax in a disposable foil pan and
floated it in the pan of water, Then I boiled the water which melted the
wax which melts at 148° F. I placed an eight inch plastic plate on my patio
and poured the wax into it and covered the whole thing with a large lid
to keep any breeze from ruffling the surface before it had a chance to
harden. I gave it a half hour, removed the lid and carefully placed the
mirror onto the wax surface.
Then for the test. I observed Rasalhague with my Tamaya........
drum roll please!
Intercept 1.2 nm T.
--- On Thu, 9/29/11, Gary LaPook <firstname.lastname@example.org>
From: Gary LaPook <email@example.com>
Subject: [NavList] Re: Home made artificial horizon
Date: Thursday, September 29, 2011, 11:11 AM
|We spent a lot of time on this in January, go to:|
--- On Thu, 9/29/11, Randall.F.Morrow@kp.org <Randall.F.Morrow@kp.org>
From: Randall.F.Morrow@kp.org <Randall.F.Morrow@kp.org>
Subject: [NavList] Re: Home made artificial horizon
Date: Thursday, September 29, 2011, 9:18 AM
I am recently self taught at celestial navigation, using
the Dutton's and Hobbs texts over the summer so please forgive my questions
being very basic. Finding a forum like this one is a great
'land-fall' for me and I sincerely appreciate the opportunity to discuss
navigation. First, being land locked in Bakersfield California an
artificial horizon is all that's available to me and the results often
disappointing. My sextant is a Davis Mark 15 and I now use a metal
plate based, screw adjusted mirror horizon. I have just changed
to a first surface mirror but though the sights are free of ghost images,
the accuracy does not seem to have improved.
What steps can I take to improve my accuracy? Can
you give me the date of a post on this subject so I may read in your archives?
I level my horizon mirror carefully but the digital level is only accurate
to 1/10 degree. Is a more accurate level available?
I have tried colored water as a reflector but only the sun or very bright
moon is reflected enough to use. Does another liquid such as oil
reflect star light?
Will changing to a metal instrument such as an Astra markedly improve results?
Do direct calculations using the law of cosines give better results than
Pub. 229 tables?
Again, thank you for the opportunity to be a part of this
forum and for your patience with my entry-level questions. I find
this to be a fascinating hobby I was introduced to by my Dad some 30 years
ago when he let me tag along at the USPS Seamanship and Advanced Piloting
classes he attended. He had done some celestial navigation in B-17's
in the pacific theater during WWII.
Randall F Morrow PT
Senior Physical Therapist
Ergonomics Safety Consultant
Chronic Pain Program
Department of Physical Medicine
Kaiser Permanente - Kern County - Bakersfield
Phone: 661-852-3677 (Tieline - 378)
Fax: 661-852-3516 (Tieline - 378)
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|Patrick Goold <firstname.lastname@example.org>
Sent by: email@example.com
09/29/2011 05:59 AM
Please respond to
|[NavList] Re: Home made artificial horizon|
Well, I built a set-up much like this, as followers of a previous thread
on artificial horizons will recall. Results were not pretty. With
the help of others on this list, who supplied me with precision leveling
legs and a very very accurate level, who put me on to a good source
of front surface optical quality mirrors and who directed me away from
plastic as a base, I got somewhat better results. Still not great.
It has been weeks since I have seen a decent night sky. If
they appear again, I will take some systematic sights using this a.h. and
share the statistics. Do the same for sights using the river and
correcting for dip short and compare.
On Thu, Sep 29, 2011 at 6:58 AM, Randall Morrow <firstname.lastname@example.org>
If you are fortunate enough to live near the ocean you will have a natural
horizon to use to take your sextant sights. If you are land-locked as I
am an artificial horizon is a necessity. Davis Instruments sells a liquid-based
artificial horizon with its own sun shades. But any shallow tray or dish
with water or oil can also be used as an artificial horizon.
The problem with both of these lies in the nature of liquids. First they
take time to settle before the reflected image can be used. Second, even
the slightest breath of wind will disturb the surface making sights impossible.
The Davis unit does have walls and a cover making the wind less of an issue,
however, the angled walls of this device could restrict you to a narrow
angle of view of bodies you can observe without moving the unit. Neither
of these will allow you to make sights of faint light sources like stars.
Any liquid, whether water or oil, will absorb much more light than it reflects.
The sun, moon and very bright planets might appear as a reflection but
most stars will not. Early explorers such as Lewis and Clark would use
a tin of mercury as a reflector but as mercury it is highly toxic and difficult
to manage it is neither practical nor recommended.
The solution is to use a leveled mirror as a reflecting surface. A mirror
horizon can only work properly if the reflecting surface is absolutely
level. Since a liquid seeks its own level no device is needed for perfect
level to be achieved. For a mirror though, a leveling system is needed.
I have found that a satisfactory level can be achieved with a 3 screw leveling
system in a 6 to 10 inch diameter plastic or metal plate. The accuracy
of leveling can be checked by eye with a quality torpedo level and careful
inspection. Select a level with the lines being close to the edges of the
bubble. Wider gaps in the lines on a spirit level make judging accurate
alignment more difficult.
A better solution is to use a digital level. I found a Craftsman digital
torpedo level that sells for under $40.00 and measures to within 1 tenth
of a degree. You don’t need the flashlight it takes to see a bubble level
since the digital display is lighted. To set up and level the mirror before
a run of sights takes about 5 minutes. The display numbers bounce around
for a few seconds but with a gentle touch, a few turns of the leveling
screws can bring you to 0.00 quickly.
The plate and leveling system can be made at home in 30 minutes and for
about $20.00. A ¼ 20 drill bit and tap set can be purchased for about $7.
A plastic cutting board ¼ inch and about 9 x 12 inches is less than $3.00.
The screws and nuts will be under $5.00. A 6 in square or round hand mirror
is around $5.00. The tools are a saw, hand drill and a cheap T-handle for
the tap. A protractor is used to mark the angles between the holes 120
degrees apart but if it’s not exact it won’t matter.
First mark off the cutting board to change it from a rectangle to a square.
Saw the excess off with a jigsaw or hand saw. The plastic is very easy
to cut. Next use the protractor to mark the holes locations at 120 degree
angles. Drill the three holes and clean off any plastic scrap with a pocket
knife or sandpaper. Use the tap in the T-handle to cut the threads into
the plastic. The mirror is attached to the base with squares of foam double
stick tape at each corner. Thread the 1&1/2 in wing bolts though the
holes and screw on the cap nuts and tighten them. The rounded heads of
the cap nuts give a centered footing so the board does not move as the
bolts are turned while leveling.
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Dr. Patrick Goold
Department of Philosophy
Virginia Wesleyan College
Norfolk, VA 23502
757 455 3357