Astralabe,asrtralobe

[Wansworth]

In the ría de Vivero where we are looking at a yacht to buy they recently found a unique Astrralobe,probably fell out of the hands of a 15 th cent uary navigator as he was practicing taking a sight?

 

[Gary Fox]

In the ría de Vivero where we are looking at a yacht to buy they recently found a unique Astrralobe,probably fell out of the hands of a 15 th cent uary navigator as he was practicing taking a sight?

Butterfingers! I imagine he would have been flogged or reduced to the ranks for such an expensive fumble.

 

[johnalison]

If they want to find out how to work it, Chaucer wrote a treatise in the subject. I tried to read it once, in a book of his collected works, but I don't think that I got very far.

 

[Gary Fox]

If they want to find out how to work it, Chaucer wrote a treatise in the subject. I tried to read it once, in a book of his collected works, but I don't think that I got very far.

Chaucer? Incredible, I didn't know he was into navigation.

 

[AntarcticPilot]

If they want to find out how to work it, Chaucer wrote a treatise in the subject. I tried to read it once, in a book of his collected works, but I don't think that I got very far.

A Treatise on the Astrolabe - Wikipedia

You learn something every day - I'd heard of it but for some reason never associated it with Chaucer! As Chaucer wrote in Middle English, I think you did well to even try and tackle it.

 

[Spanjaard]

This is the baby....




Made of copper, 21 centimeters in circumference and 4.92 kilos in weight

 

[Gary Fox]

We did 'The Miller's Tale' at school, and I only remember the filthy bits. (Mostly involving gentlemen of the cloth..)
I don't think his Treatise on the Astrolabe would have been teachable to excited teenagers..
Was Geoffrye himself a sailor?

 

[AntarcticPilot]

We did 'The Miller's Tale' at school, and I only remember the filthy bits. (Mostly involving gentlemen of the cloth..)
I don't think his Treatise on the Astrolabe would have been teachable to excited teenagers..
Was Geoffrye himself a sailor?

No; he was basically writing a "popular science" version of a Latin treatise. The astrolabe wasn't really a practical navigational instrument - apart from anything else, its horizontal reference was achieved by simply hanging it from the top ring; I think you can imagine how that would go on a boat, except on a millpond! But knowing about the astrolabe was part of the repertoire of an educated gentleman in those days; it was used for time-keeping and keeping track of seasons etc. There wasn't the distinction between astrology and astronomy that we observe, either, so a lot of its functions - even sensible ones - were described in astrological terms that we find odd.

A navigator would probably only use an astrolabe when in port; I think it was more a status symbol than something that they used at sea. Incidentally, the one @Spanjaard shows doesn't look complete; there should be another solid plate with scales and other things inscribed on it.

 

[Gary Fox]

Thanks AP

 

[johnalison]

A Treatise on the Astrolabe - Wikipedia

You learn something every day - I'd heard of it but for some reason never associated it with Chaucer! As Chaucer wrote in Middle English, I think you did well to even try and tackle it.

I have the Oxford paperback edition of his complete works, in Middle English but modern type. I set myself the task of reading the lot. I think the astrolabe was one of my few failures. I find that if you read it fast enough and just playing it through phonetically in your head most of the meaning comes, just stopping occasionally going back and checking the glossary.

 

[zoidberg]

I think it was more a status symbol than something that they used at sea.

Like most of the sextants on board 'Solent Navy' yachts.....

 

[rotrax]

Like most of the sextants on board 'Solent Navy' yachts.....

Your jibe was uneccessary.

Why would anyone require a sextant in the Solent? Mk 1 eyeball pilotage is all that is required there.

I know many who own sextants, few who ever use them.

Technology has overtaken their regular use.

A valuable tool and skill to have when making ocean passages but not in the Solent.

I think you will find few "Solent Navy " yachts with one aboard in the real world.

 

[Topcat47]

While the one found was well past it's use-by Date, Astrolabes were precision instruments, not guessing sticks. I had the privilege of project managing a modern copy of the 1548 Hartmann Astrolabe held by the Royal Observatory in Greenwich. The astrolabe had six plates designed to be used at different lattitudes engraved with extraordinary precision. It is worth noting that it would only work in the Northern hemisphere.

 

[AntarcticPilot]

While the one found was well past it's use-by Date, Astrolabes were precision instruments, not guessing sticks. I had the privilege of project managing a modern copy of the 1548 Hartmann Astrolabe held by the Royal Observatory in Greenwich. The astrolabe had six plates designed to be used at different lattitudes engraved with extraordinary precision. It is worth noting that it would only work in the Northern hemisphere.

Yes, they were (or could be) precision instruments - I didn't mean to imply otherwise. My comments were more to do with their utility as a navigational instrument for use at sea; clearly, their use of suspension to give the vertical reference is inadequate for maritime use. But navigators would probably use them to determine the latitude of ports or anchorages.

 

[Gary Fox]

Didn't Sir Robin K-J cross the Atlantic using one, to see how it all worked in practice?

 

[AntarcticPilot]

Didn't Sir Robin K-J cross the Atlantic using one, to see how it all worked in practice?

I don't know about that, but it wouldn't be reliable for several reasons. I've already mentioned that it used hanging from the top ring as it's vertical reference, and there was no provision for using the horizon; they only had a single set of alidades. The other issues are that it was direct sighting; you had to look at the body whose elevation you were measuring. Fine for moon and stars, but not fine for the sun - no shades. Finally, although it was a precision instrument, there was no Vernier or micrometer - they hadn't been invented yet. So, given a diameter of (say) 20cm, the length of the circumference would be about 63cm, so a degree would be less than 2mm. So your very best accuracy of reading might be quarter of a degree. Land based astronomers used enormous circles to gain accuracy on the order of better than a minute of arc, but a portable instrument was more limited. Finally, the requisite astronomical tables either didn't exist or were very crude!

 

[Gary Fox]

I don't know about that, but it wouldn't be reliable for several reasons. I've already mentioned that it used hanging from the top ring as it's vertical reference, and there was no provision for using the horizon; they only had a single set of alidades. The other issues are that it was direct sighting; you had to look at the body whose elevation you were measuring. Fine for moon and stars, but not fine for the sun - no shades. Finally, although it was a precision instrument, there was no Vernier or micrometer - they hadn't been invented yet. So, given a diameter of (say) 20cm, the length of the circumference would be about 63cm, so a degree would be less than 2mm. So your very best accuracy of reading might be quarter of a degree. Land based astronomers used enormous circles to gain accuracy on the order of better than a minute of arc, but a portable instrument was more limited. Finally, the requisite astronomical tables either didn't exist or were very crude!

I am posting this not to contradict you but because I am interested.
This is a bit from when he was interviewed by Andy Schell of 59 North. He also wrote a scientific paper about it, which is a free pdf to those with academic credentials.

 

[AntarcticPilot]

I am posting this not to contradict you but because I am interested.
This is a bit from when he was interviewed by Andy Schell of 59 North. He also wrote a scientific paper about it, which is a free pdf to those with academic credentials.View attachment 124468

I'm pleased that I worked out the accuracy pretty closely! But I'd like to know how he overcame the problem of using it on an unsteady platform; that seems to me to be the main problem. I presume that he only got a latitude when conditions allowed; of course it will only give latitude.

 

[Skylark]

Slight drift…….

What does the panel think about the Nebra Sky Disc about to be exhibited at the British Museum, on loan, courtesy of Germany?

 

[Wansworth]

Didn't Sir Robin K-J cross the Atlantic using one, to see how it all worked in practice?

Yes