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COUNTING SUNSPOTS WITH A $10 OPTICAL TUBE ASSEMBLY
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COUNTING SUNSPOTS
WITH A $10 OPTICAL TUBE ASSEMBLY
Copyright 2022, Boris Starosta
The seed for this project was sown by an article in the March 2021 Reflector (p.24 by John Briggs, "A Funny Thing Happened in Solar Physics"), which led me to Solar Observing Project: Re-calibrating Historical Sunspot Observations in the Journal of the American Association of Variable Star Observers, here: <https://www.aavso.org/solar-observing-project>.
Because of my interest in "real science" accomplished by way of amateur astronomy, I was keenly attracted to this sunspot observing program. But with various other projects of mine in an unfinished state (and many continue on that way;-), it took me over a year to get around to building the needed "vintage" solar telescope. But finally I got going on it, and this is just the beginning of the story.
Executive Summary: With a minimal outlay of expenditure, you can do "real science" solar astronomy. All it takes is building a very simple telescope, and thereafter an occasional 15 minute observing session in sunny weather. The work is relaxing and makes for a nice break in the middle of a busy day (or the morning, or the afternoon, whenever the sun shows itself!).
Background: The work is coordinated by Leif Svalgaard of Stanford University. You can see a nice resume of his ongoing projects on this page <https://svalgaard.leif.org/research/>, where several of the links/URLs relate to the sunspot counting research. The aim of this particular project, is to improve the utility of sunspot counts that were done in the 17th and 18th centuries by various astronomers.
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Typical Staudach drawing of sunspots. The red circles are modern - highlighting the difficulty of not knowing how Staudach defined sunspot groups. |
The largest database was created by Staudach, who observed and counted sunspots for some 50 years in the second half of the 18th century. To make this old data useful, one has to calibrate it, so that it can be compared to present day sunspot counts. Here's a nice review article on research that relies on such historical data. https://oxfordre.com/physics/view/10.1093/acrefore/9780190871994.001.0001/acrefore-9780190871994-e-9.
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The red lines are ancient counts, with most-recent calibrations to the modern data by Svalgaard. |
Today's telescopes enable the detection of many more sunspots than was possible three hundred years ago. So if you want to compare that ancient data with modern results, you need modern data acquired with ancient telescopes and methods. This is the point of the Svalgaard sunspot counting project, which he has "crowdsourced" out to the amateur community. And by "crowd" we're talking about less than a dozen observers worldwide, most of whom cannot observe every sunny day. (As it happens, presently there is only one member on the team, who is observing on a "daily" basis, and they are in the not so often sunny Netherlands. With my own efforts, I hope to make that two "daily" observers.) Thus, I am sure Svalgaard would be happy to find a few more participants - as amateurs into astro-imaging know, more data means less noise in the final results.
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This chart shows recent modern telescope sunspot counts (smaller, closed symbols) compared to Svalgaard's concurrent ancient telescope sunspot counts (open symbols). |
BUILDING THE TELESCOPE
My total out of pocket expense in this project is about $10, spent on a 50mm diameter bi-convex lens of 100cm focal length that I ordered off eBay. This was the most expensive component in the project. To approximate a typical 17th century scope, I actually want only 3/4" aperture with the 100cm focal length, so the lens from some reading glasses of 1-diopter strength would have worked, but likely would have cost more! (...and wasted half an eyeglass, which goes against my philosophy).
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My first (and only) purchase: an "Optically True" double convex lens. Cost: £7 postpaid from England. |
As it happened, this lens was the perfect size for a press-fit into a 2" shipping tube, of which I have several. While the press fit was probably good enough, I wanted to secure the lens against possible bumps and impacts in use, so I put glue inside the upper edge of this tube, then pushed the lens back in, up against the glue. I'm building this scope solid, for the ages!
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To ensure good collimation, I rested the tube on my workbench, lens side down, while the glue cured. If the lens was going to settle in position, this way it would settle flush with the end of the tube, presumably normal the the axis of the tube.
Anyway, as part of this effort to simulate the performance of a 17th Century telescope, I figured if the collimation was off a bit, it could only enhance the intended functionality.
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After a day, the lens looked lovely and secured. You can see the glue overlapped the edge a little bit behind the lens, and also seeped through to the front edge in a few places. Perfect. |
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The shipping tube was known to be too short (only about 70cm). A second tube would be added, and to keep the two tubes stable after joining, I figured a piece of wood would do the trick. I did not buy a piece of wood, I found a scrap piece about the right size lying about in the basement, and secured the first tube (with the lens) to the wood with tape. Admittedly, I also had a nice Orion EQ3 mount just lying about in the basement, having recently been retired from holding my maksutov. |
To get the plank into the mount, I modified a smaller piece of wood (2x2?), making it into a "dovetail" to fit into my Orion-type mount clamp. This 2x2 piece wood is permanently screwed onto the "spine" 1x4 plank of wood. On the side where the clamping screw comes in, I put a metal plate to take/distribute the force of the clamping screw. Otherwise this would end up splitting the wood. |
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On the opposite (passive) side of the clamp, I put two screws to take the forces into the wood.
The screws absorb and distribute the clamping force. On this side, the clamp "bites" into the dovetail with just two wedge-shaped teeth. This wood is too soft, so needs the screws to take the force. |
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Next I needed to know how long to make the second tube, so that an eyepiece held at the end of the joined tubes would produce an in-focus solar image. This length was going to be a little farther than the focal length of the lens, but I needed to know how much. My intent was to avoid the ost of a focusser, and make the tube a length suitable for one particular old eyepiece I had found in my junk box. I envisioned some minimal focussing capability by sliding the eyepiece back and forth within a simple holder.
Prototype scope out on the deck with only the objective tube attached, to measure focus distance. |
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I figured that counts as first light through this telescope, though the scope was only about half finished. After taking my measurements, I cut the second shipping tube to just the right length, so that the eyepiece would be held at best focus, when this tube was simply joined to the tube with the objective lens.
Just like my luck with the objective lens, I discovered that a 2" to 1.25" eyepiece adapter similarly perfectly press-fit into the shipping tube (I have yet to glue it). Admittedly, now this might be the most expensive part of the scope (they cost about $20), but this component is not absolutely necessary. It was just very convenient, obviating the need to kludge together an eyepiece holder. |
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After joining the two tubes, I took everything outside again to check on focus. This is the full aperture prototype. The only thing still needed is the camera obscura box at the back, and some kind of cap that will limit the aperture to 3/4 inch. |
This is the camera obscura box I made using an Amazon shipping box of approximately the right dimensions: big enough to hold a 1/3 letter size sheet, but not too big or heavy. Using wood screws I attached this box to the 1x4 wooden "spine" of the scope. Note the cutout on the end of box, to allow the tube and spine into the box a ways. |  |
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My shipping tubes had come with plugs, and I decided that cutting a 3/4 inch hole into one of these caps was the easiest way to stop down the objective aperture. After cutting the hole with a box cutter - and not too neatly, either - I used silver HVAC tape to make the cap opaque. I was afraid that a translucent bright white cap might reduce contrast too much in the final image. Maybe I worried too much? No way to tell, but I knew that even in the 17th century, anyone making a telescope was not going to have a bright white ambient light source surrounding the objective lens (as seen from the eyepiece)! |
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After making the cap opaque with the tape, I spray painted the inside of the cap with black paint, to reduce possible internal reflections. That probably was going too far!
Stop cap added in front of objective lens, the scope is basically finished! The aperture looks off-center? Nothing gets in my way to reproduce the subtle flaws of ancient technology. |
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MAKING OBSERVATIONS
Soon after everything was put together, I got my first sunspot counting image sketched. Now, notice how uneven and mottled the solar disk appears? That's because of dirt inside the old eyepiece. When we got the first-light solar images using the full 50mm aperture of the objective lens, those smudges and blobs were not visible. But with the narrower ¾-inch aperture, now the dirt inside the eyepiece is casting very noticeable shadows, which interfere with identifying sunspots.
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In this photo of my first sketch, you can see I penciled in the location of a few sunspots, onto some recycled paper I brought out. This was a prototype - actual routine observations are going on clean paper!
The above compares a more recent of my sketches to that of another team member in the Netherlands, both made on May 15. He is using a larger aperture, and the scope is on a very stable permanent mount, in a dome (It's the middle scope in the photo - a galilean optical design, 30mm aperture, beautifully built of machined tube and other custom parts)... ideal for careful sketching/drawing of features. He observes many more spots than I do. But compared to what I could find of ancient sunspot drawings (easy: google "staudach sunspots"), mine look about right in terms of level of detail. Although, the dirt in my eyepiece is getting in the way (literally!), and I will soon clean it (I'm waiting on a tool for taking it apart).
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In the meantime, I've found that using a stereoscopic technique and digital contrast enhancement, facilitates seeing the sunspots and gets me an amazing amount of detail - but I'm not using these techniques to do my actual counts. After an observing session, on any given day, I take a picture of my sketch and email it to Svalgaard. That's all there is to it. For my own future reference purposes, I also take a stereo photo of the solar image. That way, if ever there's a need for more data, it can be extracted from the photography, as shown here. |
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I encourage anyone with a minimum of technical facility to build their own vintage solar telescope, and join with me on the sunspot counting journey. Next to the study of Earth-grazing asteroids, I can think of no more important branch of astronomy. Aside its obvious ties to climate change science, solar astronomy is extremely important to our understanding of, and ability to predict flares and coronal mass ejections, which have the potential to devastate modern society (google "Carrington Event"). |
A technical illustrator and 3d photographer by trade, Boris Starosta shares his passion for astronomy with family and friends in Charlottesville, Virginia.
- Ford Prefect, highfnum, Jaimo! and 20 others like this
20 Comments
Sir, this is a familiar topic. I have just recently been looking at lenses for building a very similar scope. Can you provide a source or part number for the lens?
This is very cool. I have an old refractor, which has a lens cover with a two inch diameter stop down aperture. I have a mylar sun filter I can put over the lens cover and I could take a photo of the solar surface with my iPhone. If I used an eyepiece with a magnification of 25X, would that be too much for this purpose?
Thanks for posting this idea.
-Larry
This lens from Surplus Shed, for $1.50, will do it:
https://www.surpluss...tem/L1918D.html
50mm x 1000mm
I have several of these for making Galileo facsimile scopes.
I use 2" cardboard tubes also, they are just right. Galileo used cardboard tubes himself, I'll bet sunspot spotters (sunspotters?) did the same.
Maybe not needed for this project, but the inside of the tube is easily blackened by pouring diluted flat black paint through it.
I also wanted to participate in this project, so I bought some lenses on ebay, identical to the one shown in the article (the box is completely identical), but the optical quality turned out to be so poor, they can barely form a recognizable image. I bought four, and one of them turned out to only have 70cm focal length. The three others are so horribly poor, Jupiter is a giant smear, 1/10 the size of the Moon(!). On either side of focus, Jupiter is drawn out in a long string, almost the width of the Moon... And this is at 25mm aperture. Optically true my butt. Galileo's scope was vastly superior.
Clear skies!
Thomas, Denmark
After obtaining the 50 mm x 1000 mm objective lens from SurplusShed, I have a few questions about assembling this telescope. Can anyone help?
-For the tube, can 2” PVC pipe be used (perhaps) instead of cardboard? It’s just something I might want to consider.
-Where is the best place to start looking for 2” diameter cardboard tube?
-What is the best way to mount the objective lens? What sort of glue should be used?
-For the ocular, I am thinking of mounting one of several Huygens eyepieces I have collected. Is a simple slip tube the best way to approach focussing?
Any suggestions are most welcome!
CS,
Brian
Careysub, Love the photo of the great poet/short story writer/essayist, Jorge Luis Borges. Been reading him since1971. Still thrills me!
I got 2" cardboard tubes from FedEx stores, I also found them at OfficeMax. It is a standard size mailing tube, very common. You can also order them on Amazon, or other on-line shipping supply stores though they usually cost more since you can't buy just one and there are shipping charges.
I mounted the lens using low profile adhesive weather stripping to make the support just inside the front of the tube, then using silicone or E6000 styrene-solvent based adhesive - but literally any household adhesive will work. I would use one though that allows you to remove the lens later in case you want to reposition or something.
Slip focusing works fine. You can make a slip focuser by cutting a small segment out of a piece of 2" tube and taping it back together.
I think cardboard is easier to work with that PVC (not that that is hard) since it takes adhesive and paint well and is easily cut. You can apply a waterproofing sealant to it if you like (paint can do that too depending on type).
I like to use him as an avatar because although he was blind most of his life he had cosmic vision.
Thanks, Careysub! Great suggestions!
Really like your reasons for using Borges’s photo.
Brian
Sorry for the delay in my reply! The lens I got from an eBay seller "Spiratronics" - <https://www.ebay.com/itm/121183854320> For this sunspot counting project, any simple lens, bi-convex or planar-convex, with a focal length of approximately 100cm, will do. So if the above item is not available, do not despair.
Thanks for that tip! I probably should have blackened the interior of my tube, but did not think of it. Now I am several months into my time-series of data with this scope, and will not change (i.e. improve) it. But what I might do is make a second one, blacken the interior, and see if the results are any better.
Thomas: I only ever purchased one of those "optically true" lenses, so I know nothing about the consistency or predictability in their quality. It does seem to perform as expected... Maybe I just got lucky? I'm curious about this, because maybe mine is just mediocre, and I could get a better one?? I've already placed an order for two of the $1.50 Surplusshed.com lenses that Careysub recommended. I plan to build a second "galilean" scope and compare results, just out of curiosity. Anyway, Leif Svalgaard's sunspot counting project prefers a diversity of observers, along with a diversity of optical systems in use (approximately 1 meter focal length, 1 inch aperture), because actually very little is known about the optics that the ancients used.
Is your knowledge of Galileo's telescope performance based on what you've seen of his drawings, or do you have other sources?
Sprayed two coats of Rustoleum camouflage flat black into my cardboard tube on top of a single coat of gray primer (primer is an easy precaution). Good stuff. Very flat, very black.
Did you use a 1700s eyepiece design?
Neat project and all but... If one "google(s) "Carrington Event"" they will find nothing but page after page of those who buy into the scaremongering and next to nothing on all of the failsafes and failovers in place that would mitigate much of the alleged 'sending us back to the stone age' destruction served up on the silver platter of click bait. Long wave EM, which is what we would experience, is only really an issue over long runs of wire. You know, like telegraph lines, or high tension power wires. High tension power lines that have pyrobolts to blast the line free if things get too spicy, and automatically actuated (some pneumatically) bus bar breakers, and block after block of disconnects and safeties that keep common every day things like lightning from frying your TV, where the only real issue is wild fires. And to some extent the massive transformers in city vaults. Yes, we would end up with outages, particularly when the grid completely disconnects literally everything at the slightest wobble during the event. However, no, not everything will fry. That view is entirely based on scare tactics using a few fires from the telegraph age (remember? long interconnected wires with little to no safety in place? remember that time? yeah, keep it in mind...) when we didnt have small electronics. SMALL electronics. As in far below the wavelength of EM that would happen. How good is your wifi router at picking up LW radio? Its not. Its crap at it. Wanna know why? Of course you dont, because "ERMUHGURD DA SUHN GERNNNA KEEL US!!!" sells better than being physical sciences literate. I cant count the number of times Ive driven by a 50kW radio tower and had my phone blow up in my pocket....oh wait, it hasnt. Or the videos people that film near million watt radio towers and their camera glitches out.....oh wait, it doesnt. Or when someone keys up their however-many-watt HAM rig and fries their laptop.....OH WAIT, THEY DONT!!! Our electronics are not on a size scale that will meaningfully interact with a strong, long, EM wave. Sure, some might glitch out and reset. but they will reboot just fine. Magnetic storage you think? Yeah, the thing about that is you need a rapidly oscillating (ie, short wavelength) EM field to affect that. if you bring the background magnetic field uuuuuuuup then dooooooooown most if not all of it will stay in tact. At least in tact enough for error correction to rebuild lost bits. Same thing with the traces in our small (remember? small? ESD protected? not from the telegraph age? remember?) electronics, unlike a tuned antenna perfectly matching the wavelength of an EM source, the difference between the traces will not be greater than the brakedown voltage of any piece within them. Again, at worst the power monitoring circuits will trip and just simply turn them off.
Will there be some destruction of utility industrial level equipment? Most likely. Will there be fires? absolutely. Will some electronics release the smoke? Sure, Ill put a dollar on that bet.
Will we be thrust into mad max times for the rest of our days because apparently our modern society can fathom living a few days or weeks without power? .....Well...... Lets just say I wont be traveling to Detroit during that time.... otherwise NO!!!! For the most part, backup generators will not be affected. Stores (with access to back up power, and I dont know if you noticed, portable generators strong enough to keep super market freezers online exist. Like they have been a thing for a long time) will still be able to keep their fridges cold. There is plenty of back stock of canned foods (no little jimmy, I dont care if you like lima beans, eat them or go to bed), dry foods, food making products (if you dont have some bread making yeasts in the cupboard....what are you doing with your life? Other than spreading scaremongering BS from ancient aliens levels of arrogant shysters....and feeling superior for it....), there are trees with fruit on them, plants with berries in them, animals to hunt..... So long as that gym rat alphabro douchenozzle neighbor you've whipped up into a frenzy over civilization ending cosmic events doesnt kick your door in, shoot you with his favorite AR-15 (short barrel, fore-grip, green laser, holo sight, you know the one, the one covered in every tacticool QuarterMaster addon he can get his hands on and calls Michelle), and take all your supplies....then for the most part we, as a species, will be fine. As long as people take the time to stop, think for a second, possibly ....GASP.... ask someone with experience with the types of systems they are afraid of being affected, and evolve the personal integrity to not prey on the ignorance and gullibility of their fellow man perhaps even act with some level of civil respect and responsibility that is.....Otherwise, yeah its the hordes of the ignorant that will usher us into the stone age, not the effects of a large CME.....
By the way, all you people already typing out replies, I have $20 that says EVERYTHING you have to say about those types of events comes from conflated opinions based on reports of the Carrinton Event fed to you over the course of decades from TV shows looking for shock value ratings. EVERY. SINGLE. WORD. I dare you to have an original thought. I DARE you..... So, go on, regurgitate that same tired garbage about electronics frying (addressed above) or transformers exploding (addressed above) or massive fires (addressed above, and agreed with no less). Put on a display your facade of intelligence which is nothing but peeling layers of echo chamber enforced lead paint. Show us how you follow like a good little lamb.
PS - yes I am aware of starfish prime. It knocked Hawaii off the grid. Notice how they didnt get thrust into the stone age? Notice how it just blew some equipment (connected to long electrical lines, by the way.... remember those?) with laughable, even flat out illegal, levels of electrical protection by todays standards? Yeah. If you only get your information from the history channel or discovery or (sadly) the science channel, you have no idea what you are talking about. A magnet past a coil, and conflating a city exploding erasing all industry and stored data across the planet because 'oh look! long power lines! EVERYBODY PANIC!!!' does not knowledge make. I would end with a satirical "change me mind" but why should I offer to be open minded to the people who already closed theirs off after it fell out?
No. Simple two element Kellner, 25mm f.l.
To participate, there is no requirement to have an exact replica vintage telescope. Just the approximation of one.
Hi Larry: I am sorry that I am late to comment on your post. I am thinking that your old refractor would most likely be a doublet - two lenses. For this project, in an attempt to get telescope performance close to that of Staudach's telescope, we should have only a singlet lens which is what all of us in the project are using. It has been suggested that the aperture for this project should be about one half inch to three quarters of an inch in diameter. You wouldn't need any mylar film - instead you should project the image of the sun on something like a piece of metal or cardboard or masonite where you clip a piece of ordinary paper, and then you draw the sunspots that you see, with a pencil. The idea is to duplicate, as much as possible the original conditions and methods. So that wouldn't include photographs at all. Just drawings.
Cool project! So, was the tube total length 1 meter?
Yes.