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Gary:

I'm so frustrated with mirrors that I'm ready to switch to mercury.
But how expensive is it, how much do I need, and where do I get it?

David C.


On Nov 27, 12:56 pm, Gary LaPook  wrote:
> Gary LaPook writes:
>
> I know that I may still be the only only person left using mercury for
> an artificial horizon but it is superior to any other substance due to
> the quality of its reflecting surface.  I know all the warnings about
> the dangerousness of this liquid ( which of course varies with the
> amount of exposure to it, read "Mad Hatter", and a navigational use of
> it is very limited in time and the number of occasions per year and it
> is used outside) so of course you must be careful, don't drink it, use
> in well ventilated area, store in an airtight bottle not in the house,
> etc. I have been using a small bottle of this stuff for over 40 years
> now and it allows me to take clear shots of Polaris, a second magnitude
> star with ease.
>
> A couple of years ago there was a show on TV here which dealt with
> celestial navigation. The illustration that they used to show the change
> of altitude and determining latitude at noon was to rent a panel truck
> with a large flat side. They parked it pointing south and leveled it
> fore and aft then put a rod sticking out from the side of the truck on
> the top so that the rod cast a shadow of the sun on the broad side of
> the truck. Starting in Minneapolis they marked on the side of the truck
> the shadow of the rod cast by the sun at noon. They then got in the
> truck and drove south and the next day they were in Louisiana where they
> repeated the experiment and this showed the  very obvious difference in
> the height of sun due to the change in latitude of the truck. I was
> pretty impressed by this method of illustration.
>
> gl
>
>
>
> Isonomia wrote:
> >Alex,
>
> >whilst in theory a reflected artificial horizon isn't difficult to
> >use, in practice the two suns appearing and disappearing in the view
> >finding and moving in opposite directions take quite a bit of patience
> >to work out and to begin to get results.
>
> >Whilst I would have no problem instructing an adult, my experience
> >with trying to instruct children is that whilst they were
> >concentrating they were incapable of accurately expressing what they
> >saw in the viewfinder and as I can't see what they are seeing and so
> >don't know what they are doing wrong (or even right) I can't help
> >them! So the whole thing was frustrating both for me and for them.
>
> >In contrast it will be easy to tell children how to adjust a "sextant"
> >using a shadow and set to measure an angle like a theodolite.
>
> >If I do use a sextant, at the very least, I've got to find alternative
> >solar filters so that the two images of the sun are different colours.
> >That way there is at least a simple way to refer to them: "can you see
> >a red sun then ..." - "can you now see a blue sun then ..", "is the
> >blue sun above or below the red sun ... turn the knob left/right...",
> >etc.
>
> >A few child friendly instructions:-
>
> >Turn left,
> >Turn right
> >Look down
> >Look up
> >Tilt to the left
> >Tilt to the right
> >Turn the knob clockwise
> >Turn the knob anti-clockwise
>
> >When you tilt the sextant from side to side, do they cross so that
> >both suns are in exactly the same place?
>
> >Don't you dare drop it on the mirrors!
>
> >Mike
>
> >On Nov 27, 4:01 pm, Alexandre E Eremenko 
> >wrote:
>
> >>Mike,
>
> >>>I'm camping next summer with a load of 11year old kids
>
> >>And you want the kids to participate in your celestial
> >>observations?
>
> >>>In particular I would like to build a form of "sextant" based on
> >>>measuring the angle above a horizontal plane of the sun using the
> >>>sun's shadow.
>
> >>As I understand from your message you DO have some sextant,
> >>and your problem is with artificial horizon only.
>
> >>>1. How to create a horizontal plane to within
> >>>a few minutes accuracy?
>
> >>I know three ways of doing this. I list them in the order
> >>of decreasing accuracy.
>
> >>a) Usual liquid artificial horizon.
> >>It is NOT HARD to catch the Sun
> >>with ordinary sextant and artificial horizon. Not much harder
> >>than with natural horizon.
> >>I can give simple
> >>step-by-step instruction
> >>based on my experience. I never had difficulty catching the Sun.
> >>But at night it is much harder, and I found it almost impossible
> >>with the stars, even if you pre-set your sextant. Accuracy
> >>1' is easily achieved with Sun if there is no wind and there is
> >>a stable platform.
> >>b) Air sextant. Can be bought on e-bay for under $100.
> >>If you are lucky and get a working one, it gives you about 5'-10'
> >>accuracy. Members of this list recommended MKIX, I bought one
> >>for $40 (plus shipping) and I am reasonably satisfied with it.
> >>One advise: if there is a choice, give preference to one
> >>WITHOUT clock-work averager. The thing is useless on land and sea,
> >>and takes almost 1/2 of the weight of the device.
> >>c) "practice artificial horizon" sold by Celestaire for
> >>about $25. This is much worse than an air sextant in preformance,
> >>but fits in your pocket.
> >>d) finally, if you don't have a sextant and don't want to buy a real
> >>one, and 20 miles accuracy is OK, and you are willing to
> >>use Sun only, there is another option which I did not try seriously
> >>myself but my friend Bill did, and with satisfactory results:
> >>a German cardboard make-it-yourself sextant. Bill claims that
> >>he achieved 5' accuracy which I did not verify, but it is reasonable
> >>to expect you can achieve 20'. Its artificial horizon is better
> >>than the Chinese junk horizon mentioned in c).
> >>This sextant is also sold by Celestaire.
>
> >>Alex.- Hide quoted text -
>
> - Show quoted text -
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