The World's First Reflecting Telescope
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- čas přidán 2. 06. 2024
- This video presents a discussion between Robert and mirror-maker Terry Kubecki-Pearce. The subject under discussion is a replica of Isaac Newton's telescope that was presented to leading members of the Royal Society in 1671. Terry and Robert both collaborated on the manufacturing of the replicas in 2009, and one of the aims of the project was to explore the technologies and methods Newton would have used to make his world-changing instrument. As mirror-maker for the project, the discussion with Terry centres on the difficulties he had forming an accurate optical surface on the small metal blanks and the light this throws on Newton's efforts to produce the world's first reflecting telescope three hundred and fifty years ago.
Along with his life-long experience as a telescope mirror-maker, Terry is one of the brains behind Vacuum Coatings, a London-based company specialising in the deposition of evaporated metals on glass (for telescope mirrors) and other surfaces using a vacuum chamber.
Diary date: Terry will be appearing on the BBC's Sky at Night on Sun 12 Jan 2020 (at 22:00 GMT) where Maggie Aderin-Pocock goes back to her childhood telescope-making class, where she was one of Terry's pupils, to talk basic telescope essentials. One of the replica telescopes featured in this video may - if they haven't cut it - make a brief appearance in the programme.
Below is an index that will take you to specific parts of this video.
00:00 Introduction to the replica of Isaac Newton's telescope
03:42 Meeting Terry and chatting about personal history and our first meeting
11:52 The telescope discussion begins with a brief instrument overview
15:18 Looking in Terry's lunch box
17:13 Newton's polishing journey
24:56 The hand mechanics of the polishing method
29:38 If it's good enough for NASA
38:47 The provisional nature of Newton's specula and the 1671 telescope 'laboratory'
43:30 Concluding observations
46:25 Further reading and closing remarks
The monograph referred to at the end of the video:
Newton's Telescope An Examination of the Reflecting Telescope Attributed to Sir Isaac Newton in the possession of the Royal Society. By A.A. Mills and P.J. Turvey Vol. 33 No. 2 March 1979
The 'How to grind a mirror for a telescope' video that Terry refers to in the video can be seen by clicking the link below.
• How to grind a mirror ...
Presented by Robert J Dalby FRAS
Produced by DB Video Services for Astronomy and Nature TV - Věda a technologie
Newton's genius has been my obssesion since high school. Your impresive video just adds up to this obssesion.
Wow what a video ,A standing Ovation my friend
Awesome video guys, liked and shared!!
I haven't seen a ball joint like that before, pretty smart.
It was used before. Here is Tycho Brahe's instrument using the same idea. media-cdn.tripadvisor.com/media/photo-s/17/0a/57/60/tycho-brahe-museum-pa.jpg
They are pretty popular for off roading motorcycles. Ram mounts, they are used for accessory mounts and even for rear mirrors.
They handle abuse very well, because when you hit something, the ball allows the thing to rotate, instead of breaking and being lost on the roadside.
I just stumbled onto this channel by accident. I've always had a thing for astronomy and I don't know why it took me so long to find it.
This was a fascinating and wonderful video! LOVED It!! Could have watched another hour!!
Absolutely great video! Priceless stuff indeed!
Thank you very much, gentlemen!
Brilliant video, so interesting! Thanks Guys.
Great video guys and happy new year
What a delightful video. With a lovely British uniqueness to it, makes med proud of my fellow Brits. Thanks so much for uploading these videos, please keep them coming.
Thanks both for a very informative and entertaining video. Are you going to do a report of the view from this scope? Cheers
John and Terry Pearce - the memories come flooding back! I am another ex-mirror-maker (Brian Crabb).
Absolutely fascinating, thanks ever so much.
What a pleasure watching this.
Interesting video 🔭
Great channel.
Due to this channel I actually bought a Sky Watcher 127/1500 AZ GTI today.
Hey guys! I’m just wondering if you are planning on uploading any more V-2 content or maybe some V-1 or even Redstone missile vids? Love the channel!
Thank you. Very educational. 👍
Als wir in unsere Sternwarte Spiegelschleifkurse abhielten, wurde die Brennweite mit der "Lichtmesstrecke" (ein schwarzangestrichener Flur im Keller, von etwa 7m länge) überprüft, bevor sie zum bedampfen gingen. Nach dieser Messung wurde dann die Tubuslänge festgelegt und der Punkt wo der Seitenspiegel montiert wurde.
Btw. : Wernher v. Braun war Vereinsmitglied bei uns und bei uns wurde auch Mondgestein ausgestellt. Auch haben wir den Funkverkehr der Apollo gehört.
Very intresting video...Newton was a local lad and went to the same school as my two sons!
Really excellent channel. Your presenting style and knowledge are outstanding. Do you have a shop?
A query about 'figuring'. My (limited) understanding is that forming/polishing using the surface of a cannon ball will give a spherical mirror, but a parabola is required for the Newtonian telescope. Is the term 'figuring' - as frequently used in the discussion - about the difficulty of moving from a spherical to a parabolic shape AND with an optically polished surface? (If so, this could have been stated a bit more clearly for the uninitiated.)
Hi Mark, and thanks for posting. You might have been misdirected by a bit of tedious 'Ye olde internet forum lore' that tries to convince the unwary that a Newtonian telescope must have a parabolic primary, to the extent of denying the name Newtonian to any instrument possessed of a primary mirror with a spherical figure. It's twaddle of course, the ripe kind of twaddle you only find on the internet. The majority of Newtonian reflectors that exist in the world (and manufactured month-in, month-out) are of the spherical figure type. And a good job too - as it would all get a bit awkward, ruling against the eponymous original, when we reflect that every primary mirror made by old Mrs Netwon's precocious lad Isaac was of spherical figure. Our discussion deals with the difficulties that Newton had forming a useful optical surface at all, the fine distinction between parabolic and a spherical figure was quite beyond the reach his rudimentary methods. Our point was that Newton would have struggled to reliably achieve a useful optical surface, as opposed to a merely shiny reflective one, on his specula (made from an alloy of copper and tin with the addition of whitening agents) in more or less than same way that Terry did when working up our aluminium mirrors. He would we are sure have achieved an optical surface just once with the procedure he was employing. If he tried to promote the surface with additional polishing - to look more like the ordinary shiny metal mirrors of his day - he would almost certainly lose the useable optical surface and be unable to bring it back again; regardless of how long he polished it for. It would have taken considerable trial and error effort to discover this frustrating situation. He clearly did master the problem - but he would have needed to tolerate a mirror that looked quite dull by the standards of normal household metal mirrors available since Roman times. KR RJD A&NTV
@@RocketPlanet The majority of Newtonian telescopes made are also garbage department store telescopes like the "PowerSeeker" that seems to outsell every other telescope on Amazon and elsewhere. It has an f/4 spherical primary that is stretched to f/8 with a single-element plastic lens mounted in the focuser that functions as an uncorrected Barlow. The problems are that the severe spherical aberration of a 127mm f/4 spherical mirror remain uncorrected, and the permanent "Barlow" introduces chromatic aberration, spherochromatism, and possibly other aberrations. It is indeed a Newtonian telescope, but to be a decent one it really needs a paraboloidal primary mirror (which would suffers from coma toward the edges, granted, but provides much sharper images on-axis). 76mm or even 114mm f/8 spherical primary mirrors are perfectly fine for decent budget Newtonians, since their spherical aberration is limited, but larger and/or faster telescopes really should have paraboloidal mirrors to be worthwhile. Who, these days, would want to buy a large, heavy, expensive Newtonian that isn't even corrected for spherical aberration?
Of course, these are all telescopes, whether they are good or bad by modern standards, or worth or not worth the money. Galileo's and Newton's telescopes are really bad by modern standards, but that's OK for that era, not so much for the present. Trying to give good purchasing advice to beginners is not a form of "Internet twaddle". Maybe some go too far in making their point, claiming that a Newtonian *MUST* have a paraboloidal (which most people mistakenly call parabolic) mirror? Well, that is incorrect, but I haven't seen much of that. And they probably just mean that if you want a good Newtonian of a large aperture and/or fast focal ratio, then it needs to have a paraboloidal mirror (or a Schmidt corrector--something to clean up the image, at least on-axis), or else it won't be a good telescope by modern standards. That's true enough.
I just watched the original review video and jumped into this one right after...Same dude but decade later with the same telescope. Pretty trippy.
Very cool!
The first reflecting telescope was the Gregorian (James Gregory, a contemporary of Newton) and first built up by Robert Hooke. The first practical reflector was the Newtonian, which may have been built by Hooke at the behest of the Royal Society for Newton. Hooke demonstrated many such experiments, of his own methods and those of other members, to the Royal Society. As Hooke had built the first reflecting telescope, the Gregorian, the Newtonian was the logical next step.
Hi Jeff. Thanks for posting, but I'm afraid I don't recognise the history you are presenting here. There is compelling evidence that Robert Hooke built the earliest Gregorian telescope, not the first reflecting telescope: that priority belongs to Newton. It's worth remembering that the mid 17th century was a very different time from our own, and even Newton's great solution for a telescope free of chromatic error took another 50 years to catch on. KR RJD N&NTV
@@RocketPlanet . Gregory's reflecting design was published in 1663 and pre-dates the first practical reflecting telescope, the Newtonian telescope, built by Sir Isaac Newton in 1668. The Gregorian was first built up and demonstrated in 1673 by Robert Hooke. As Newton and other such gentlemen of the time were no mechanics, it was normal for Hooke to demonstrate to the Royal Society, he was the man for that. There was some contention between Hooke and Newton, but Hooke probably had the Newtonian assembled by artisans, or not, Newton was not a Fellow at the time (demonstrated to King Charles II in 1672 and admitted same year). The Gregorian is important as it led to the Cassegrain telescope.
Ok, so I have extracted much of that from Wikipedia but as a physicist it's stuff I learnt at school and college. The annals of the RS are well kept and are available.
Neither were entirely new ideas, Galileo and others had discussed using mirrors and Newton had probably read Robert Gregory's 1663 book, but Gregory had been unsuccessful building it up, it took Hooke the artificer to do that. One might argue that Hooke's work with springs and elasticity is just as important as Newton on gravity and motion, they do in fact all work together.
Newton's objective however was not as a telescope but to prove white light consisted as a spectrum of colours, which was possibly more important to science - the chromatic aberration was a key finding (NB). The original is in the possession of the Royal Society. Also cf Royal Museum Greenwich.
@@RocketPlanet Hooke and Newton did not play well together. In 1686 Hooke claimed it was he who had given Newton the idea for gravitation. With good cause, but denied. Demonstrating the earlier reflecting Gregorian may have been a dig at Newton's claim to the first reflecting telescope.
The ball it is mounted on is such an ingenius idea.
Like your channel! 👍
There's so much that ordinary people like me don't know about instrument making. Thanks.
i hope terry is in good health, i would love to meet him one day, what a legend
Great video. Lots of work, knowledge and passion put into it.
Like it a lot, glad I found your channel.
How did you make the tube?
Thank you.
Hi Adiano, and thanks for your post. When we started the project we had no firm idea about how many of the replicas we would manufacture - somewhere between 10 and 50 was my guess pending difficulty and cost. I made a couple of tubes from paper and paste, hardening them with shellac and lubricating them with wax. But it was labor-intensive and somewhat hit and miss in terms of the final result, both in terms of look and function. In the end, to make sure we had a reliable product, we went to a specialist paper tube manufacturer in England and had a hundred of each tube made to our specifications. All that was required was to dress the final surface of the tubes inside and out. If it looks 'too new', bear in mind we were not trying to make a simulacrum of the surviving relic held by the Royal Society. Our aim was to make something that approached the look and performance of Newton's 1671 instrument as it would have been at the time. KR RJD A&NTV
@@RocketPlanet
Do you have any replica still available? Would like to know the price if it is.
I want to make a replica also for my personal challenge.
So far yours is the best I have seen.
I'm slowly collecting all the informations and tools so I can to make it one day in my free time.
Thanks for the reply.
Have a good day.
Lovely video. I suspect the issue with the Cerox not working on the aluminum is the hydroxyl group chemistry where bonds are formed with Si in the glass and then sheared off. That wouldn’t happen with the aluminum with its oxide formed.
Brilliant
Okay so I’ve just gotten a new reflector telescope and I’m a little cautious on how to acclimate it to temperature. Does any body have any tips?
Great video! I used to think that the Comet Hunter Newtonian was an awkward design by allowing the adjustment of the focal length by moving the secondary, but now I see that Newton did it himself. You should do more videos like these on the history of different telescope designs. Cheers
There was a lot of technology for making curved surfaces at that time to make a lens. Probably the brass like alloy was easier to machine than aluminum just like it is today for many alloys. Very fine polishing compounds can be made by collecting granite dust and floating it,
It's strange listening to this as it seems to be using classic glass lens grinding techniques. The first thing I thought of was a pendulum or plumb bob style grinder. The pendulum length would equal the focal length, the resting pendulum would be the center of the grind, a screw adjuster at the top of the pendulum could adjust grinding depth. This way it cannot round the edges, it cannot form other than a perfect arc surface shape if set correctly, the mirror stays still and you polish using a dome-shaped grinder on the end of the swinging pendulum.
I know nothing of making these things, but to me this seems a logical method from an engineering viewpoint, a very simple to make apparatus using the wood and brass of the time. It would make each subsequent mirror the same as the grind cannot escape the arc length of the swinging grinding rod as it will always move in a perfect arc.
Am I missing something? As I said, I know nothing of grinding these shapes, but hand grinding as described seems like a very troublesome way of doing it, especially for such a small mirror.
i know this is like 30 years too late but i feel like if you used a harder metal it would be easier to polish. i’ve noticed on soft metals like silver (possibly aluminum too) that a low grit gives better polish, then when you move on to the high grit it becomes cloudy again. the same doesn’t happen with hard steels
They might have given him knowledge on polishing the metal in exchange for not telling those things to others and for using them to mass-produce the telescope, if it became popular.
Why you are making less videos?
Probably because they take a lot of time and effort.
wasn't the 1st newton telescope radial in stead of parabolic, and wouldn't that make the polishing easier?
Are handmade mirrors superior to machine made?
No, the accuracy and quality of maschine made mirrors has increased so much during the last century. It is virtually impossible to match the performance of a maschine made mirror with a self made model. That said, it is still a very satisfying experience to build a telescope all by yourself. If you are interested, the dobson model should be the way to go for you: czcams.com/video/snz7JJlSZvw/video.html
Tea leaves were the secret polish. As it does not clump together as minerals do.
I wonder if Sir Newton used item deemed to dangerous to work with like Mercury. As a child my father showed me how to polish a dime with Mercury from a thermometer in my hand. This was the mid 70's I sprayed the barn with Ortho 48% nicotine sulfate and rode in the hatch back of my sisters Ford Pinto. I wasn't effected at all. I wasn't affected at all.
Is the replica to scale with the original or is it smaller?
As soon as I saw it I thought hmm, very nice half scale model
Glass has awesome properties.🔃
Right, maybe Newton tried to make the focal ratio short/fast simply because he thought he could, since chromatic aberration was not an issue with mirrors. Of course, this turned out to have challenges and aberrations (e.g. more severe coma) of its own, but frankly I would have thought and tried the same thing. The long/slow focal ratio telescopes of that time were unwieldy and had less aperture per size and weight--ridiculously so because of chromatic aberration--so given the definite nonexistence of this aberration, why not try for the most aperture possible in a handier form factor? If for no other reason, it was a proof of concept, and small telescopes are easier to handle anyway. Easier means you can have a larger aperture than you could ever dream of having in a refractor, and this principle carries over to the present day with all modern professional scientific telescopes.
Why is bringing the mirror to a polished finish make it not work?
I suspect that it is because they used aluminum. When you try to polish aluminum it oxidizes almost instantly to a specular surface. It also has a tendency to smear during machining.
It appears that the original was a brass alloy and that is much easier to machine and polish.
That telescope is 400 years old but 900 years old telescope is 900 years old above. And that was made in ancient India and Cambodia....
Did you make that??? I just watched a video of a guy who has one of these identical to yours who claims they are made in Russia and in fact several are listed on Ebay from Russia today!!!
Yes we did make it. Identical? If you mean in the sense that the cars Ford are making now are identical to their Model T of 1908 in that they have an engine, 4 wheels, seats and, steering wheel - then yes they are 'Identical'. KR RJD A&NTV
Why would Newton not use a glass mirror with silver? I know precious metals are easy to work with and polish even easier. U can polish gold down to nothing by rubbing it with a kitchen towel
It's to bad the Vatican put Galileo on house arrest the last 9 years of his life for seeing the planets going around the sun and writing books about it, I think we would be a little farther in astronomy, crazy
how about you cold press a steel die into a sheet of aluminium well a disk of then all you have to do is put a shine on it