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Bruce,

Likewise, welcome aboard!  As long as Robert has decided to holler at
you from the cheap seats, I thought I would too, although I must
comment that my seats are much cheaper than his!

No, I have never seen tables for Jupiter's moons that are timed to
better than a minute.  This is probably about as good as you could
get with a lunar, or perhaps 20-30 seconds for the latter.  I've
never tried any Jupiter timings, so can't comment further.

Robert may have had a slightly prejudiced view about manufacturers of
new sextants as he failed to mention the Freiberger, from the former
East Germany (or maybe they've gone out of business?).  These are
excellent pieces of equipment and not too expensive.  I suspect they
have better construction all around than Cassens & Plath.  The
Russians copied them and produced an excellent product, but that is
no longer manufactured, to my knowledge.

The following is about metal sextants.  For the best bang for the
buck, and overall minimal contact with the instrument, by all means
buy an Astra new.  But if you're really cheap, you might wish to
venture into the used sextant game.

FRED's USED MARINE SEXTANT COMMENTS, ranked by estimated EBay cost of
2-4 years ago:

$200-400.  Here, probably the most inexpensive sextant of high
quality is the Russian SNO-T; the problem is not getting ripped off.
There are some Russian-speaking members of the list who might help
you here.  From Alex Estremko's tests, the SNO-T is probably as
accurate and precise as any sextant on the market.

$250-500.  The next most inexpensive metal sextant widely available
is probably the Husun Mate.  These are mostly suitable for position
sights, not lunars, as they usually only came with one 2.5x
telescope.  The later ones, from 1942 on, have quite a bit of
eccentricity in the arc; they may have let quality slip to increase
production for the war, not to mention the Blitz.

$300-500.  Then there are old U.S. Navy sextants.  These also have
considerable eccentricity.  They also are not as common as the first
two and often are in need of serious repair when available.  You will
see the ones needing serious repair go for prices lower than $300.

$300-600.  Friebergers.  Discussed above.

$200-500.  Then you might find various Japanese sextants predating
the Tamaya Jupiter and Spica.  These will be in various condition,
from pretty good to awful.  The frames are always(?) aluminum in
Japanese sextants, and once the salt gets in, they can get chewed up
pretty quickly.  There usually is a fair amount of eccentricity.

$600-900.  In this price range are the so-called top-of-the-line
sextants, Tamaya, Cassens+Plath, and C. Plath.  As I said already,
the C+Ps are not too hot.  The best thing about them is you can find
them fairly new, so in very good condition.  The Tamaya Jupiter is in
the same class.  Then, for really top-of-the-line, there's the C.
Plath and Tamaya Spica.  The Spica was only produced since 1972 or
so, so tends to go high because it's newer.  The Plaths were
discontinued around 1980 or so.  Tamaya has redesigned the Spica; I
don't know whether the new ones have the same quality.

Personally, I prefer my Husun Mate as it's more compact, but still a
6" arc, the light can illuminate your notes, and it's easier to
handle with an artificial horizon because the handle isn't tilted.
It's also solidly built: no glue.  I wish it were possible to
calibrate it without tremendous effort; but it'll put me within a
mile of my location.  I wish I also had a more powerful, usable
telescope.

If you haven't used a sextant before, it will take you 3 months to a
year to become proficient in handling them.  The largest source of
error with an artificial horizon is timing the shot.  A tripod to
hold the sextant also would help immensely.

Good luck!

Fred Hebard

On May 3, 2008, at 11:15 AM, Robert Eno wrote:

>
> Welcome aboard Bruce. I will weigh in on a few things even  though
> the bar
> is likely closed for the evening.
>
> Just a few observations from the cheap seats.
>
> Robert
>
>
> ----- Original Message -----
> From: "Bruce" 
> To: 
> Sent: Wednesday, April 30, 2008 10:27 PM
> Subject: [NavList 4956] Introduction
>
>
>
>>
>> Anyway, that is my rambling introduction, but I have a few
>> questions for
>> the list.
>>
>> 1)Sextants are expensive precise instruments, but they are still
>> made of
>> brass and aluminum. Why does no one use invar to make them more
>> resistant to thermal expansion?
>>
>> 2) It is supposed to be possible to get exact GMT by observing the
>> moons
>> of Jupiter, but I have yet to find any tables that have more than a
>> minute accuracy.  Has anyone else tried and had better luck?
>>
>> 3) I have looked, and bid on, several a-12 air sextants on e-bay. Has
>> anyone ever had a good result with an e-bay A-12?  Are they fairly
>> rugged? I hate buying a pig in a poke, but celestaire is not cheap
>> (like
>> me).
>>
>> 4)I have heard that it is possible to modify am A-12 to see the
>> horizon
>> by inserting a prism somewhere. Has anyone done it, and can it be
>> done
>> so that the bubble can still be used.
>>
>> Here is a very old Norie's online.
>> http://books.google.com/books?
>> id=OzwEAAAAQAAJ&printsec=frontcover&dq=norie%27s
>> +nautical&lr=&as_brr=1
>>
>> Thank You
>>
>> Bruce Hamilton
>> Vancouver, BC, Canada
>>
>> bruce.hamilton    (antispam you know what goes here) shaw.ca
>>
>>
>>
>>>
>>
>
>
>
> >



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