Are antique sextants any good?

[stormalong]

Originally Posted by Wotname

Well, here is one way; no need for measuring height or time!

https://en.wikipedia.org/wiki/We,_the_Navigators

Marvin Cramer used the word sight. I am aware of "the navigators".

Observations and sights are two different things.

Look, we can go back and forth on this forever if you are obstinate enough but you can't change what Marvin Cramer said in his interview.

[IslandHopper]

Originally Posted by stormalong

Marvin Cramer used the word sight. I am aware of "the navigators".

Observations and sights are two different things.

Look, we can go back and forth on this forever if you are obstinate enough but you can't change what Marvin Cramer said in his interview.

I know exactly what terminology Creamer used and i also know and understand the context of it, the only issue here is, you don't.....

https://www.naturalnavigator.com/new...amer-monument/

https://en.wikipedia.org/wiki/Marvin_Creamer

[SeanPatrick]

One can observe the Sun or Moon as they just touch the horizon and compute a line of position or time sight without a sextant. The "sextant altitude" (Hs) is simply 0°0.0'. Of course, refraction right at the horizon can be tricky.

Originally Posted by roverhi

[Lunars] took so much time and math to compute that they were finally dropped when accurate chronometers became generally available and affordable.

Lunars actually didn't take very long, even using tables - and the math wasn't any more arduous than what was required for standard sight reduction. Still, "longitude by chronometer" is arguably easier and therefore became the standard practice.

[Epikur]

If you are looking for a cheap sextant look up Bris Sextant. A genius invention by (as far as I know) Bjarne Bris.
It‘s virtually for free (you have to build it yourself or buy it from Bjarne for small money)
It’s inherently accurate. Actually the most accurate sextant possible.
Problem is you have to calibrate it yourself, but you are learning what a sextant is.

I put it in front of my old binoculars and got a perfect sight.
NEVER look into the sun by binoculars without strong filters. I used green welding filters (the small round type, actually for soldering) for one of the glas sheets of the Bris Sextant.

[SeanPatrick]

The Bris is a real, usable instrument. However, it is very limited in its use, not the easiest thing to make and needs to be calibrated by someone with at least a cursory knowledge of celestial navigation.


I would not recommend it for someone just starting out. I really wouldn't even recommend it to anyone as a primary CN tool. As a backup/novelty ... sure.

[Franziska]

Here is a video about it. It's really a clever simple device from a very clever an unusual man.

https://youtu.be/pm79kH2BBMY

Getting one as backup or for the grab bag seems really a good thing to do.

[Lake-Effect]

Originally Posted by Epikur

If you are looking for a cheap sextant look up Bris Sextant. A genius invention by (as far as I know) Bjarne Bris.
It‘s virtually for free (you have to build it yourself or buy it from Bjarne for small money)
It’s inherently accurate. Actually the most accurate sextant possible.
Problem is you have to calibrate it yourself, but you are learning what a sextant is.

I put it in front of my old binoculars and got a perfect sight.
NEVER look into the sun by binoculars without strong filters. I used green welding filters (the small round type, actually for soldering) for one of the glas sheets of the Bris Sextant.

This is so cool. Thanks.

Here's a link to the inventor's site. It looks like he sells them for 200 Euro, which isn't that cheap.

I've looked at some drawings, but none yet show the angles, or more construction details. I'd be grateful if anyone had a link to detailed drawings.


{edit - just found this}

[Franziska]

https://en.wikipedia.org/wiki/Bris_sextant?wprov=sfla1

&

https://web.archive.org/web/20131013...read_more.html

[GrowleyMonster]

Originally Posted by Lake-Effect

This is so cool. Thanks.

Here's a link to the inventor's site. It looks like he sells them for 200 Euro, which isn't that cheap.

I've looked at some drawings, but none yet show the angles, or more construction details. I'd be grateful if anyone had a link to detailed drawings.


{edit - just found this}

Angles and dimensions are not critical and have zero effect on accuracy because you are not trying to build to a predetermined scale or angle. And that is a good thing, because you would be very unlikely with common shop tools to be able to create an instrument accurate at a particular given angle or scale. Just a slight variation in clamping pressure or glue viscosity would be devastating if you took that approach. The approach of the Bris device is just to make the unit, and then figure out what the angle is when you have the body on the horizon. I say "the" body but there are actually multiple reflections so you have multiple angles that you can shoot. That is the calibration. Just observe and then calculate from a known position what the Ho must have been. Actual use involves waiting for the body to meet the horizon in the instrument, rather than adjust the instrument to bring the body down to the horizon. When the body and horizon meet, you know the Ho because it is what you found it to be in calibration and testing. The only variable is the time of the observation. So you get the GHA and dec from the almanac for that day, interpolate for observation time, and enter your sight reduction tables or formula, whichever you use, for the solved intercept and azimuth.


It is because it is not adjustable and not built specifically for a particular angle or set of angles that it can be so simple and so small. And cheap and easy to build. The original form factor is convenient because you can hang it from your eyeglasses and use it hands free, and still be able to see around you. It would still work if you used old sextant shades or welding goggle glasses or random bits of glass as long as one was at least about a #9 welding shade with good UV blocking to protect your retina. If you wanna do it, just do it. It will work. Tweak the dimensions to suit you.


<EDIT> for your safety, consult the eclipse watching community about which number shade to use.</EDIT>

[Franziska]

Actually thinking about the 200€.

If you do not have the money for it, fair enough, I guess Sven Lundin would be one of the last persons to be crossed with you if you built your own.

If you have money, it would be a kind gesture to buy of him and this way thank him for coming up with this, support his adventures and pay for the manufacturing.
I'd think the ones he sells might even come with a calibration (not sure).

Seems a fair trade to me.

[charliehows]

arguments about navigating without instruments are specious - where do you draw the line? Humans were forced to navigate without reliable instruments/maps/whatever for 3000 years, the rate of loss was - astronomical. I reckon you could circumnavigate now just by getting a position by radio from any sighted ship. Your odds of survival would be - reduced...and what would be proved?

[Franziska]

Not sure if that's the point of this thread.
Sextants and derivitates are instruments and have successfully be used for navigation for a very long time.

To have one and use it as backup for a GPS seems a good thing to me. Alternatively the other way around with Sextant and a GPS as backup.

The Bris Sextant is a Sextant and a very clever one indeed. Not even moving parts which could get misaligned or be damaged.

Who was suggesting not to use any instruments here?

Originally Posted by charliehows

arguments about navigating without instruments are specious - where do you draw the line? Humans were forced to navigate without reliable instruments/maps/whatever for 3000 years, the rate of loss was - astronomical. I reckon you could circumnavigate now just by getting a position by radio from any sighted ship. Your odds of survival would be - reduced...and what would be proved?

[Franziska]

One more source on the Bris:

http://www.fer3.com/arc/sort2.aspx?s...y=1996&y2=2019

[charliehows]

well - the point of this thread - if there is one - is whether antique sextants are any good - without specifying 'what for'; i was mainly responding to the arguments about the guy (Cramer?) who travelled 'without instruments'; good for him but ... why? But I'll admit its a digression.

to return to the point; my argument about whether you would seriously navigate with an antique sextant - the history of navigation is largely a history of serious collective effort to avoid disaster. In general everything that could help was used. Its only in the modern era that we have individuals setting out to travel and experiment with various theories about to what extent one uses the collective knowledge of navigation in their endeavours.

I kind of doubt whether someone asking about buying an antique sextant for $100 is actually ever going to be in a situation where the use of the instrument for a position fix is either necessary or possible; but even if it were so, the level of reliability and accuracy of a $100 handheld GPS is, at least for the present, about 1000 times better than any position derived by sextant (antique or no), chronometer and almanac.

[IslandHopper]

Originally Posted by charliehows

well - the point of this thread - if there is one - is whether antique sextants are any good - without specifying 'what for'; i was mainly responding to the arguments about the guy (Cramer?) who travelled 'without instruments'; good for him but ... why? But I'll admit its a digression.

to return to the point; my argument about whether you would seriously navigate with an antique sextant - the history of navigation is largely a history of serious collective effort to avoid disaster. In general everything that could help was used. Its only in the modern era that we have individuals setting out to travel and experiment with various theories about to what extent one uses the collective knowledge of navigation in their endeavours.

I kind of doubt whether someone asking about buying an antique sextant for $100 is actually ever going to be in a situation where the use of the instrument for a position fix is either necessary or possible; but even if it were so, the level of reliability and accuracy of a $100 handheld GPS is, at least for the present, about 1000 times better than any position derived by sextant (antique or no), chronometer and almanac.

The OP specified for "to practice celestial navigation".... try reading the OP!