Instructables

Low Tech HELIOSTAT. How do I attach the suntracker?

I recently made a solar accumulator which is a limited heliostat, I guess. It can only send the light to somewhere on the axis of the equatorial mount.
The new heliostat is different. It should be able to send the light just about anywhere you want and keep it on that spot as long as the sun shines.
This feature could be massively useful for solar cooking (multable heliostats shinging light on one area) water heating or solar lighting, (shining the light into dark corners or northern windows).
I want low tech ones that poor people who do not have computers can make.
I am pretty sure this works now after making a little model. I am using gimbals on the real thing having seen a problem on the model. Thanks to all who helped me choose gimbals for where it joins to the equatorial mount!
The theory follows on the next couple of pages.
Brian
 
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Step 1: Basic optics

When sunlight hits a mirror, it bounces off at the same angle as it hit the mirror.
The plane of the mirror is exactly at right angles to a line bisecting the bouncing lightrays. I think we should focus on the bisecting line!
If we allow the mirror to swivel on its centre point, and tie the corners of the mirror to somewhere on that line and keep it taut, the mirror will point at the correct angle to send the light to the target!

Step 2: Like a KITE

Picture of Like a KITE
If we get 2 similar elastic bands and tie them together, and tie ones end to the sun pointer and the other ones end to the target pointer, where the bands are tied to each other will define a point on the bisecting line.
Furthermore, the kite mirror will now be pointed in the right direction as long as the sunpointer follows the sun.
Nice effort! For anyone looking for a turn-key solution, see the H1 heliostat over at http://www.lightmanufacturingsystems.com/heliostats . It uses a metalized PET mirror, which is unusual.
Gentlemen:
I have been working on this for  about 7 months now.  An equatorial mount does work at equinox as you say with a 48 hour rotation or any day with a 24 hour rotation if the target is in line with the polar axis (principle of coleostat). At redrock heliostat website, 3 mechanical heliostats are shown: Focalt, Gamby, and Silberman.  The last two suffer from gimbal lock when the sun and target are closer than 30 degrees, there is a good article on this in Wikipedia.  I have not been able to understand the Focalt mechanism yet. It seem as if the tape, rubber band and corkscrew methods might also have mirror control problems at low sun, target angles.
gaiatechnician (author)  danie1murphy3 years ago
Daniel Murphy's latest work can be seen on this video.   (I have other easier projects where I can contribute more!)
I think if you pause the video from time to time it is easier to understand what he means. Brian
gaiatechnician (author)  danie1murphy4 years ago
Good to hear from you!  I abandoned it for a while.  I think last time I emailed with you we noticed that a reference picture of a Gamby had the equatorial axis  pointing the wrong way.  Correct? 
But really glad that you have made progress.
When we know the problems beforehand, we can make arrangements to move the target or heliostat  to get round  the problem during year!
I have made progress on tracking (turning the equatorial mount)!  I have a fuller sized image at http://solardesign.ning.com/photo/liquid-piston-tracker and I may do an animation too.

Gimpequafloatpistons.jpg
gaiatechnician (author) 5 years ago
I have been looking into a heliostat on equatorial mount with a 48 hour rotation. I have not been able to conduct experiments due to clouds. Even if the 48 hour rotation does not work perfectly, it may be part of the solution. If it is "nearly right" then all that is needed is a 24 hr rotation for the sun pointer to make fine adjustments to the angles of the mirror. This means no huge swings on the gimbal (perhaps a small ball joint is all that is needed). Like the ball joint in a tractor 3 point linkage. What do you think?
PAsolar5 years ago
A complete heliostat system is available at
http://www.eastcoastsolarsystems.com/heliostats/ .

Check it out.
rimar20005 years ago
Hello, I had a similar idea a time ago, and I never got to develop it totally. Seemed in its objective, but nothing with the rubber band. The equatorial mount by itself is sufficient. If the sun takes 24 hours a turn, we only needed a mechanism that gives a turn in 48 hours. for example, the hour axis of a clock, geared down four times. In this way, if at sunrise dawn? we put the mirror to 45 degrees on this axis, so that the reflected ray upwards vertically, at noon the mirror will have to be horizontal, and to the dusk again to 45 degrees in the opposite direction. This approach must be duplicated symmetrically to the equatorial axis, so that the following day the process can be repeated. But the sun is not easy to convince, and it is guided by its own temperament. It would be necessary to make almost daily adjustments to the approach, because there are no mechanic ways to follow the sun in the sky. Pardon my "automatic translator" English.
Sorry. The 48-hour rotation idea won't work, except in one case. That case is if the date is one of the equinoxes and the target direction is on the celestial equator. In other situations, it may seem to work at sunrise and sunset, but not at other times of day.

For example, suppose you are on the equator at an equinox, so the sun rises due east, rises straight up the eastern sky, passes overhead at noon, then goes vertically down the western sky to sunset. And suppose you want to reflect light due north, horizontally. At sunrise, the mirror must point horizontally north-east, so light from the sun on the eastern horizon will be reflected to the north. And at sunset the mirror must be aimed north-west. So, you might say,the mirror turns 90 degrees in 12 hours, so that's 48 hours per revolution, with the axis of rotation vertical.

But that would mean that at noon the mirror is pointing due north, aimed horizontally, and that won't work at all! In order to reflect light from the overhead sun toward the northern horizon, the mirror would have to be aimed upward at 45 degrees. Your 48-hour rotation won't do that.

We have discussed some heliostat designs that work. A mirror that rotates once every 48 hours won't. Sorry!

And it *is* possible to follow the sun mechanically. It doesn't have any "temperament". Its motions are highly predictable.
I don't agree.

If the assembly is equatorial, my 48 hours rotation idea functions EVER, be equinox or solstice or intermediate. Your assumption of an equatorial subject is yours, not mine. Please rethink that thing.

About the "equation of time", that is to say the movements of the sun in the sky, the mechanical complexities of a device that keep in mind them, they are larger than what a person can confront. Or, if you prefer it, the relation cost / benefit is too high so that be worth while.
Here is an example of a mechanical
"Equation of Time" heliostat.
http://www.redrok.com/neat.htm#US4368962
The gears and stuff calculate the "Equation of Time".

The heliostat head is quite close to a Silbermann
heliostat which is driven with a constant speed
clock drive which is good for a few days but needs
mechanical adjustments. See:
http://www.redrok.com/main.htm#mechanical
Hultberg fixes these errors.

Duane
Yes. I know of two designs for mechanical heliostats that allow for the Equation of Time. One uses a cam-and-lever device, with a cam that rotate once a year and is shaped so its radius is basically a graph of the Equation of Time. The other makes use of the fact that, to a fairly good approximation, the Equation of Time is the sum of two sine waves, one with a period of six months and the other with a period of a year. Two rotating cranks, one turning once a year and the other twice, can be linked so that a motion like the sum of two sine waves is produced. As far as I can see from the diagram on your website, the Hultberg machine works basically as the second of the above designs. There are probably other ways to do it, too. But, nowadays, that kind of technology is kind of archaic. Mass-producing the machines might be fairly cheap, but hand-making them one at a time would be very tedious. It's so much easier to use a computer! David
You need to look at the patent.
http://www.redrok.com/neat.htm#US4368962
Just click on the patent # and Google opens the
full patent. Hultberg shows 2 embodiments one with
1 crank and the other with 2 cranks. Presumably
the 2 crank version is a bit more precise.

Duane
Yes. I did skim through the patent. I didn't study it in detail, but as far as I can see, the design *should be* capable of great accuracy. The limitation I can see is that the gear ratios must, obviously, be ratios of integer numbers of teeth on cog-wheels, which means that they are unlikely to be exactly right to match the astronomical parameters: the number of days in a year, the tilt ("obliquity") of the earth's axis, the eccentricity of its orbit, the dates of perihelion and the vernal equinox, and so on. So the machine may be good, possibly *very* good, but not perfect.

But I am puzzled as to WHY Hultberg went to all the trouble and expense of inventing this machine and patenting it. The patent reads like something from the 19th Century, but actually it was filed in the 1980s. The cog-wheel technology shown in the diagrams was already being replaced by computers. (Actually, in one of the claims, computers are mentioned. It looks like he realized at the last minute that this new technology was about to supersede his invention, so he tried to claim it too.)

I doubt very much that any of these machines have been made except for Hultberg's own prototype.

Fun, though.

David
Thanks, Duane. I need the apparatus for a solar kitchen, therefore I don't need precision. My discussion with David was conceptual, and I interrupted it for lack of time. We could not come to an agreement.
Every inventor eventually realizes that every simple idea has already been thought of, probably many times. If your 48-hour rotating mirror worked, we would all be using it for heliostats, and wouldn't be discussing the more complicated machines that are described on this page. Unfortunately, it doesn't work, except in the very limited case I described previously. You don't have to believe me. Try it! Just take a clock mechanism, add a 4:1 gear to slow down the 12-hour rotation of the hour hand to the 48-hour rotation that you want, attach a mirror, and see if you can use it as a heliostat. Be sure to try it with the target direction well away from the equator, e.g. to the north if you are in the northern hemisphere. You won't have to spend much money, if any, which is good because you'll be disappointed. Sorry! As for the Equation of Time, sure, it is a fairly complicated function, but it would be easy to follow mechanically. Just use a cam-and-lever mechanism. Have a shaft that rotates once a year, and put a cam (a non-circular wheel) on it. The shape of the cam should be such that a lever resting against it moves according to the Equation of Time. Then use the motion of the lever to adjust the heliostat clock so that the machine follows the Equation of Time properly. This sort of thing was commonly done back in the time when intricate mechanisms were widely used. Nowadays, we tend to use computers and electronics instead, but there's no reason why the mechanical device should not still be used. However, in the old days mechanical heliostats worked by clockwork which had to be wound up every day or two. So some sort of manual maintenance had to be done frequently, which meant that the adjustments for the Equation of Time and the variation of solar declination could be conveniently done by hand. I have never seen them done automatically in a mechanical heliostat, even though it would be perfectly possible. Anyway... Try building your 48-hour thing. Let us know what happens!
Thanks for the response, David.

When you say "...Just take a clock mechanism,..." etc, lacks to add "put the array over an equatorial mount". If you omit this step, the device does not function. You think the following thing: during a single day, and especially considering only the diurnal hours, the displacement of the sun in the sky is practically circular, be in winter or in summer. Therefore, an equatorial mount is the unique thing that does you need to trace it. You can be sure that it will not be set apart of its path more than some seconds of arch.

An equatorial mount or assembly is one whose axis of turn is parallel to the terrestrial axis, that is to say that is oriented in north-south direction, and inclined with regard to the horizontal one angle equal to the latitude of the place.

I live in Argentina, south of South America. Then, I speak Spanish. Therefore my English is not good, pardon. I use http://freetranslation.com/ and then I apply corrections according to the little thing that know of the language.

Thanks also for the cam-and-lever mechanism idea. I did not think this, I only thinked combined movements, this is much simpler. But one must say that even this method is not the last word as for an exact position, because the displacements of the terrestrial axis are not contemplated in the equation of the time, due to they are erratic and unpredictable. Obviously, the differences are despicable for the almost totality of the applications.

I did something seemed to what you suggest, three or four years ago, and functioned here in the backyard of my house, approx. 32º of south latitude, in full autumn. At least, functioned between the hours 11 and 13 approximately. As soon as it have time I will try to refloat the apparatus and I will it to work several days. It does not contemplate the annual displacement of the sun, that is to say that in this epoch I would have that to adjust the north-south inclination of the mirror almost daily.
When I say "the unique thing" I must have said "the main thing"
Thanks for your e-mails. Okay, I'll visit here to correspond with you.

I managed to see the 1843 machine to which Brian referred. For some reason, the link would not work for me yesterday. Actually, the image shows a collection of machines made by Silbermann, who was a famous maker of these things at that time.However, I cannot see any reference to a mirror turning once every 48 hours. The machines have an ingenious mechanical device for bisecting the angle between the directions of the sun and the target. The basic mechanism, defining the direction of the sun, rotates once every 24 hours.

I suspect that the person who wrote the "explanation" for Brian knows even less about the thing than Brian himself does.

I am beginning to wonder if the 48-hour machine is something like Leonardo da Vinci's helicopters - imagined and maybe drawn, but never made and tested.

Back to our discussion. For simplicity, imagine that you are at the earth's South Pole. The earth's rotation axis is vertical, with the Celestial South Pole directly over your head. Suppose the date is December 22, the summer solstice, so the sun is moving horizontally 23.5 degrees above the horizon. Suppose that the target at which you want to reflect light is in a horizontal direction, as seen from your mirror.

At some time of day, the sun will appear to pass directly above the target. The bisector of the angle between the directions of the sun and the target will be pointing 11.75 degrees above the horizon, or 78.25 degrees from the vertical axis of the earth.

12 hours later, the sun will be 23.5 degrees above the horizon in the opposite direction. The target is still where it was originally. So in what direction does the bisector now point? Almost over your head, that's where! it will be only 11.75 degrees from the vertical axis of the earth, at the same azimuth as the target.

So the angle between the earth's axis and the direction of the bisector - along which the mirror must point - varies between 78.25 degrees and 11.75 degrees during the day. So it is absolutely certain that the mirror can *not* be fixed to a polar axis, rotating only about it.

The same situation occurs, but is less simple to describe, for any other location on the earth. It is not peculiar to the poles.

As I have said so many times, please DO THE EXPERIMENT. HAZ LA PRUEBA. Forget about everything that I and others have said. Learn from actual observation. That's science.

Best wishes.

David
NO, NO, NO, YOU ARE IN ERROR:

Where you say " ...it will be only 11.75 degrees from the vertical axis of the earth",
you must say "...it will be only 11.75 degrees south of the intersection of the meridian of the place with the heavenly equator"

That is, in my latitude, "it will be approx. 21.25 degrees north of the zenith." You cannot see it?

If I could send you a drawing, I believe that you would understand it. But you have said me that cannot receive it.
NO!!!

A drawing would be misleading because it is two-dimensional. We MUST think in three dimensions. Use a globe instead.

Why do planes flying between Europe and the west coast of North America go way to the north over the arctic? Because that's the shortest route. Look at a globe (NOT a map) and you will see this is true. The mid-point of the journey between Vancouver, on the west coast of Canada, and London, England, is close to the Arctic Circle, over northern Canada, even though both cities are close to the same latitude of 50 degrees north. This shortest path is called a "Great Circle".

If the earth were transparent, an observer at its centre would see the direction of the mid-point of this Great Circle route as the bisector of the angle between the directions of Vancouver and London.

The same is true of the situation I hypothesized above. In three dimensions, the angle between the target, on the horizon, and the sun, 23.5 degrees above the opposite horizon, is in a *vertical* plane, which also includes the axis of the earth. The bisector of the angle is only 11.75 degrees from the axis and the celestial South Pole.

It is essential in this problem to think in three dimensions and to consider Great Circles, rather than straight lines, as the shortest distances between points.

Yes?
The one that has to learn something very simple are you, David.

While it travelled by train to my house I fell in account of which is YOUR problem: you don't know what signifies "equatorial assembly". I will explain it you, to see if you understand of a good time: the axis is PARALLEL TO THE TERRESTRIAL AXIS, which can be expressed also (I believe to have said before but it does not matter) in the following way:

  • It is oriented in north-south direction (or south-north, is equal)
  • It is INCLINED with regard to the horizontal plane of the place an angle equal to the LATITUDE OF THE PLACE; the highest part (if there are it) is the one that aims at the most nearby pole.
Do you understand now? If don't, don't continue, we finish here.

By the previous thing, already you will have realized that your affirmation "The angle that includes the directions of the sun and of the receiver is in a VERTICAL plan, that includes also the axis of the land and the south pole" is false, and is the origin of YOUR CONFUSION.

And I believe that we can give for finished the discussion. Too much time we have dedicated him.

Un abrazo.

Osvaldo J. Schiavoni

Osvasldo, amigo: I know very well what an "equatorial mount" is. Usually, i use the alternative name "polar-axis mount" which describes the fact that the axis of rotation points to the celestial poles, so the axis is parallel with the earth's. No. The problem we have been having is because you have difficulty visualizing things in three dimensions. This is very common. I blame the educational system which concentrates on using two-dimensional diagrams and images rather than three-dimensional models. I have the advantage of having studied Chemistry at university, where I had to model and visualize many three-dimensional structures such as molecules and crystal lattices. This trained my brain to be able to "see" three-dimensional things in my imagination, to rotate them and look at them from different viewpoints, etc.. This morning, I used my "SunAlign" program (which can be found elsewhere on this page) to calculate the direction of the angle-bisector in the South Pole situation that we discussed yesterday. It exactly confirmed the prediction I made, and therefore falsified your prediction. Try using SunAlign or any other program that does this kind of calculation. You will get the same result. I agree that we should put an end to this discussion here. It is wasting space and getting nowhere. Continue to send e-mails to me if you wish. Best wishes, David
Obviously, if your program is based on erroneous concepts, it will bring erroneous results. The computer don't make magic.
As I said, "Try using SunAlign *or any other program that does this kind of calculation*. There are plenty of other programs, most of them complicated ones that astronomers use, which I had no hand in writing. SunAlign's results have been compared with those from some other programs and are in good agreement. But, if you'd prefer not to use SunAlign, use something else. The result will be the same.
Pardon, David. I don't want to continue this discussion.
If you look around this page, you'll see that I already have a machine with a mirror that rotates about a polar axis (what you call an "equatorial mount") and which reflects light in a constant direction - toward one of the celestial poles (actually, the South Pole). This is part of my two-mirror heliostat. In order to do this, the rotating mirror has to turn once every 24 hours, not 48! The machine is real, and works, which is why I am very certain I am right about this. There are two cases in which a mirror tuening about a polar axis can work as a heliostat. One is if the target is on the equator and the date is an equinox. In this case the mirror turns once every 48 hours. The other case is if the target is in the direction of one of the poles. In this case, the mirror turns once in 24 hours. For other target directions, there is no way a mirror rotating around a polar axis can work as a heliostat. Think about it! But also get your machine running again and do some experiments. I'm glad you weren't upset by my earlier posts. I had no intention of being offensive. Best wishes, David
Sorry. I made a typo, and there doesn't seem to be any way to fix it now. I typed "tuening" when I meant "turning". I hope this doesn't confuse your automatic translator too much!
David, sadly this has become a "dialogue of deaf".

If you read and analize carefully my assertion "...during a single day, and especially considering only the diurnal hours, the displacement of the sun in the sky is practically circular..." you must realize that this is true.

My mirror did not direct the sunlight toward the pole, directed it approximately up, but similarly would be able to have directed toward any side, inside the practical limits of the construction of the apparatus, and of the laws of the reflection (example, is impossible reflecting it more than 90 degrees of the mirror's surface)
We'd have to get into some heavy mathematics to consider this problem in detail. However, I think we may be close to a compromise understanding. You originally claimed that your machine worked "EVER". (You probably wrote "siempre", which can be translated as "ever" or as "always". I'm assuming you meant "always".) Now, you're saying that it worked reasonably well. And I will agree that, if the sun and target are both fairly close to the equator, and if you aren't very fussy about accuracy, then the machine may work well enough for your purposes. (By "equator", I mean the celestial equator, which at your latitude (32 deg. south) is an arc from the eastern horizon, across the northern sky, passing due north at an elevation of nearly 60 degrees, then down to the western horizon.) If you're interested only in target directions not far from that, your machine may be good enough. But it doesn't work "always", especially not if the target is anywhere near one of the celestial poles. And if you want high accuracy (some people insist on precision to within 1/100 of a degree), then it would work only if the sun and target are both very close to the equator, which means that the date must be near an equinox. Oh well... Have fun! David
Yes, you are correct about EVER ---> ALWAYS, pardon.

But I insist, my mirror function ALWAYS because the mounting is equatorial and during some few hours the north-south displacement of the sun in the sky is despicable. Its path is practically circular.

With the 48 hours arrangement, once aimed the ray of sun light in the desired direction, the mirror will remain all the time (we say some hours) aiming at the bisector (bisectriz in Spanish) of the angle formed between the sun and the object to illuminate.
"Bisector" is correct. "Despicable" is not. I am sure you meant "very small" or "negligible", but in English "despicable" does not have that meaning. I suspect you are having trouble thinking in three dimensions. Let me start with an example. Buenos Aires and Melbourne, Australia, are both at roughly latitude 35 degrees south. Suppose a plane were to fly from BA to Melbourne, travelling due westward along the 35S line of latitude. And suppose an observer at the centre of the earth could somehow see the two cities and the plane, and bisected the angle between BA and the plane. Obviously, just as the plane leaves BA, the bisector would point toward the 35S line of latitude. But as the plane flies westward, the bisector would curve southward. By the time the plane arrives in Melbourne, the bisector would point close to the South Pole! You have been saying that since the sun, during a single day, moves along a line of celestial latitude, going in a circle around the earth's axis, then the bisector of the angle between the directions of the sun and the fixed target you want to illuminate will also travel in a circle around the earth's axis, moving at half the speed of the sun. But, in three dimensions, this is simply not true! The bisector will generally move in a path that is completely different from what you have been imagining. I realized last night that there is an exception. If the latitudes of the sun and the target are equal and opposite, one north of the equator and the other south of it, then the bisector will travel around the equator. So if, for example, your target is 20 degrees south of the equator, then your machine will work properly on the two dates of the year when the sun is at latitude 20 north. But it won't work well on other dates. And it will never work if the latitude of the target is more than 23.5 degrees north or south, since the sun never moves further than that from the equator. Does this make sense to you now? As I've suggested, build your machine and try it. One experiment is worth a million Internet postings! I may not be back until Monday, so have a good weekend. Regards, David
About despicable, I got this:

Babylon English-Spanish
despicable
adj. despreciable, astroso, bajuno, desdeñable, indigno, menospreciable, ruin, vil, zurriburri
English_Spanish by Jaime Aguirre
despicable
s.- sabandijaadj.- despreciable | vil | ruin | menospreciable | desdeñable | execrable
An English -> Spanish Dictionary (G...
despicable
(adj.) = despreciable, vil, infame
Ex: Gestation, menstruation, & pregnancy were often considered shameful and despicable.

About thinking in 3D, really is difficult and sometimes conducts to serious errors. For that reason (among others) the models from buildings from the plans are manufactured.

But sorry, I think you are in error and I am in the good way.

Perhaps you know the saying: "if you think as me, we will be friends; if you don't think like me, we will be doubly friends, because together we will be able to find the truth"
Of course I would like us to agree on the truth about this matter, but I am sure I already know it! I can imagine 3-dimensions well, and I have done real experiments and observations which support my convictions. Except in a few unusual situations, your 48-hour polar-axis rotating mirror will not work as a good heliostat. I would be happy to invite you to my house to see these experiments, but since we are about 10,000 kilometres apart, that might be difficult! So I can only urge you to do experiments of your own. Construct the machine and see if you can make it work. You'll find it is especially bad if the target is far from the equator. Maybe other people here would also like to do experiments. Please let us know the results! Until we have something solid to report, I think we should stop using space on Instructables for this discussion. We're not really instructing anyone about anything! If you want to communicate with me by private e-mail, feel free to do so. My address is: david.williams@bayman.org Write in Spanish if you wish. Later, David
Since the above message was written, "rimar2000" and I have exchanged a lot of private e-mails. I think I have now persuaded him that he may be wrong! (I am sure he is.) I know he is very busy right now at work, so he can't devote much time to this. But when he gets a chance, he will do some experiments to see whether his idea works. I hope he doesn't feel too disappointed when it doesn't!
gaiatechnician (author)  david williams5 years ago
David, i do not think your post is nice or respectful.
http://www.earlytech.com/common/show_image.phtml?Id=491390987&Item_Name=Heliostat+by+Silbermann+1843 shows how the geometry works. I do not understand it at all so I asked for an explanation and here is what I got as an explanation:
"The heliostat in that link needs to rotate at half the speed of the sun because it is trying to keep the direction of reflection constant. If you are just trying to keep a telescope or camera pointing directly at the sun then you need to rotate at the same speed. So it depends what you are trying to do, if you want to redirect the sunlight to a fixed point where you can use it to do work then 15o/hr is going to be wrong" So it appears the 48 hour thing is a hundred years old! Are you still so certain?
Brian

I tried looking at your earlytech link but got a page saying it is not yet implemented. Seems weird, but still... Anyway, I can imagine what the machine is, so let me explain it to you. First, a couple of background facts: First, in the early 19th Century the technology of making telescope lenses was not very good. In order to reduce spherical and chromatic aberrations to acceptable amounts, objective lenses had much longer focal lengths than is usual nowadays. This meant that telescopes were long and cumbersome. It wasn't easy to point them at the sky and move them to compensate for the earth's rotation. So devices with mirrors, heliostats or coelostats, were used, allowing the telescope to be stationary and horizontal while it viewed the reflection of the sky in the mirror. Second, as I have explained to both of you, "Gaiatechnician" and "Rimar2000", in private e-mails, there is just one situation in which a mirror, rotating about an axis parallel with the earth's at 7.5 degrees per hour (48 hours per rotation) can work as an accurate heliostat. Imagine that lines of latitude and longitude are drawn in the sky, and that the earth is transparent so you can see the lines even down below you. If you are located at the mirror, and if you see the sun and the target at which you want to reflect light at equal but opposite latitudes, as shown by the lines in the sky, then the mirror will work as a heliostat, reflecting sunlight at the target as the earth turns. Not otherwise. What the earlytech image shows, I am sure, is a machine in which a telescope is located at the equal and opposite latitude to that of the sun on that date. So the telescope would have to be movable so its latitude can be adjusted every day or two to compensate for the sun's seasonal movements. However, this would be the only kind of movement the telescope would have to make. The 48-hour rotation of the mirror would allow the sun to be continuously viewed through it. NOTE: Just in case anyone is thinking of duplicating this, do NOT look at the sun directly through a telescope. You will be instantly and permanently blinded. Also, do not try using a piece of dark glass to dim the light. There is a good chance that the heat of the sun will shatter the glass. There are devices called "solar diagonals" which can be attached to astronomical telescopes for viewing the sun. Buy a professionally made one and use it. Nothing else. Back to heliostats... The device I described, with the 48-hour rotating mirror, can be and presumably was used for the purpose of astronomical observations. But it wouldn't be much use as a heliostat for other purposes. The target, such as a cooking oven, would have to be located at the equal and opposite latitude to that of the sun. Unless the target is movable, the machine would work only on the two dates in the year when the sun is at the right latitude. And it would never work if the target is more than 23.5 degrees from the equator since the sun never goes further north or south than that. You can believe me or not believe me. I really don't care. But you should both be prepared to be convinced by the results of experiments. Build the machine and try it. Then see if you are still convinced it works. Actually, for the first experiment,. you don't need to use a clock. Just attach a mirror to a polar axis, aim it at noon so it reflects sunlight at a target that is well away from the equator, wait a few hours and see if you can turn the axis so the mirror reflects light at the same target. Don't be too disappointed! One experiment is worth a million words, which I about the number I feel I have written...
David, now I understand that you are saying: "The target, such as a cooking oven, would have to be located at the equal and opposite latitude to that of the sun. Unless the target is movable, the machine would work only on the two dates in the year when the sun is at the right latitude. And it would never work if the target is more than 23.5 degrees from the equator since the sun never goes further north or south than that." YOU ARE WRONG ABOUT THE DEVICE, David: the device's axis is equatorial, but the mirror don't. This is movable in all directions Then, it can reflect the solar light in all directions, inside what the reflection laws permit
Brian, that is what I try to cause to David understand, but he is so absolutely convinced of what he believes, that I don't find the way to do it.
The way to convince me would be to show me an experiment demonstrating that you are right. But that's not going to happen. I have done the experiment myself, so I know what it shows.
gaiatechnician (author)  david williams5 years ago
The link to the heliostat from 1843 works just fine. Why not study that heliostat and how it worked? It did work, didn't it? Please quit emailing me. Please feel free to publish an instructable on heliostats. I do not want to convince you.
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