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== Strange Experiences with a Heliostat ==
== Old technology ==


I am posting the following true story here since it may be instructive for anyone who is contemplating building a heliostat.
The article mentions ancient Egypt. How did heliostats work in the days before clockwork and motors? --[[User:Chriswaterguy|Chriswaterguy]] 17:18, 8 July 2010 (UTC)


:Like I said on the main page, the mirrors were aimed by hand. Basically, the "machine" consisted just of something like an easel, on which the mirror could be placed. At frequent intervals, a person - a servant or slave - would shift the easel and mirror so it continued to reflect light in through the door of the building, or whatever.


--------------------------------------------------------------------------------
:At least, that's how they still do it nowadays, to show tourists. I've been to Egypt a couple of times and seen them doing it. I assume they are using the same method as was used in ancient times. Generally, the ancients documented things well with hieroglyphic descriptions, so the methods they used are still known with relative certainty.


Back in the 1980s, I designed, built and programmed a computer controlled heliostat to bring more sunlight into the living room of my house. It was a simple machine, with the mirror in an alt-azimuth mount, so the principal axis of rotation was vertical and the other horizontal. The program that ran in its computer - an ancient Commodore VIC 20 - was developed from an earlier program I had written that calculated the position of the sun in the sky from astronomical theory.
:[[User:DOwenWilliams|DOwenWilliams]] 19:08, 8 July 2010 (UTC) David Williams
 
Describing the heliostat in detail would be pointless. It was built from components that are now long out of date. Nowadays, duplicating it would be almost impossible. Anyone who wants to design a heliostat should start from scratch.
 
However, something happened when I was testing the machine that might be worth sharing...
 
I live in Canada, about mid-way between the Equator and the North Pole. Seen from here, the sun always moves clockwise in the sky, rising in the east, passing to the south around noon, and setting in the west. Since the heliostat mirror moves to keep reflecting sunlight in a constant direction, it was obvious to me that the azimuth drive of the machine would always turn clockwise. In fact, I contemplated using a motor for that drive which would turn only in the clockwise direction. I changed my mind only because it was convenient to use identical motors in the two drives. Since the elevation (altitude) drive changes direction as the sun rises and sets, I used motors, actually steppers, that could turn either way.
 
When I first set up the machine and started testing it, I encountered a couple of simple problems that I easily fixed. The next time I tried it, I was happy to see that it initialized itself and moved its mirror so as to reflect sunlight in the correct direction. It seemed to be working properly. But, as I watched it for a while, I saw to my dismay that the azimuth drive was turning anticlockwise. Obviously, that was wrong. I stopped the machine and started hunting in the hardware and software for the cause of the problem. In that, I had no success. Everything seemed to be as it should be, but the azimuth drive kept turning the wrong way.
 
Then I made another puzzling observation. Although the mirror was turning anticlockwise, it was continuing to reflect sunlight in the correct direction! The thing seemed to be working properly, but wrongly at the same time.


After some bemusement, I realized what was going on. It was about noon on a summer day, so the sun was high in the southern sky. The window through which I wanted the heliostat to reflect sunlight was roughly to the north of the mirror, and not much higher than it. The mirror had to be aimed in the direction that bisected the angle between the directions of the sun and the window, as seen from the mirror. At that time, the aim direction was high to the *north*. As the sun moved from east to west, this aim direction also moved from east to west. But since it was to the north of the zenith, this motion was anticlockwise in azimuth. My heliostat was absolutely correctly performing this anticlockwise rotation.
::Thanks - wondered if it was that but I wasn't quite clear.


It was startling to realize that this machine, which I had designed and programmed, was apparently smarter than I was. It had correctly figured out which way to move, although my expectations were wrong.
::It's an interesting pattern, looking back in history - the very wealthy and privileged used to rely on masses of labor (servants or slaves). Even simple labor-saving devices such as wheelbarrows were not used. The Roman and Greek civilizations were surprisingly close to an industrial revolution. One major factor holding them back was that they had slaves - it was only when such labor was unavailable that there was a real impetus to develop technologies to do work. --[[User:Chriswaterguy|Chriswaterguy]] 00:34, 21 July 2010 (UTC)


Another realization was that only sheer good luck had allowed the machine to work properly. If I had used a motor in the azimuth drive that would turn only clockwise, which I had been sure would work properly, the machine would have been incapable of turning in the correct direction. I wonder how long it would have taken me to figure out what was wrong!
:::In at least a few cases, the slaves have developed the technology to put an end to their own slavery. I'm thinking of what happened in about the 18th Century, in England. Water was pumped out of mines by primitive steam engines, invented by Newcomen (?sp). Children were employed (essentially enslaved) to turn valves to send steam into and out of the cylinders. One kid, I don't know his name, managed to tie bits of string to the valves and other parts of the engine, so the engine turned its own valves and the kid could relax. However, this had the unintended effect of making the engine work a lot better. The timing was improved. The owners of the mine noticed that the pump was working better than it used to, so they investigated. Finding that the kid was now redundant, they threw him out onto the street. As a slave, he had been fed. Now he had nothing.


A few months later, as the noon-day sun sank lower in the sky as winter approached, a situation arose where the aim direction of the mirror was almost vertically upward at some time near mid-day. The angles of elevation of the sun and the window, as seen from the mirror, were equal, and their azimuths were 180 degrees apart, so the angle-bisector pointed vertically up. In that situation, a tiny movement of the bisector, as the sun moved westward, caused a large change in the bisector's azimuth. This made the azimuth drive of the heliostat turn very rapidly, about 180 degrees in just a few seconds! I hadn't expected the machine to move rapidly like that, since the sun moves very slowly in the sky. On one day, the drive spun anticlockwise, since the bisector was passing just to the north of the zenith. On the next day, the bisector passed just to the south of the zenith, and the drive spun clockwise. The reverse happened in the spring, as the sun moved northward. Of course, since the mirror was lying on its back, pointing upward, the rapid rotation about the vertical axis did not cause much change to the aim direction.
:::[[User:DOwenWilliams|DOwenWilliams]] 02:07, 21 July 2010 (UTC) David Williams


Heliostats can be very counter-intuitive machines!
:::A further thought: Western science and technology were essentially stalled until the 15th Century because of the horribly cumbersome numerical representations that were used. Can you imagine calculating the area of a circle, using Roman numerals?! Only after "Arabic" numerals were introduced into Europe in the late 1400s could calculations be done accurately and easily. This led quite rapidly to the development of science in the 16th and 17th Centuries, and to the start of the Industrial Revolution in the 18th Century. The 18th Century was also when the slave trade was at its peak, which makes me doubt whether the absence of slaves causes technology to be developed.  [[User:DOwenWilliams|DOwenWilliams]] 14:09, 21 July 2010 (UTC) David Williams


[[User:DOwenWilliams|DOwenWilliams]] 17:23, 5 July 2010 (UTC) David Williams
== AT heliostat ==


== Old technology ==
[[File:AT heliostat.png|thumb|right|200px|The AT heliostat]]
This image was put into the heliostat page today without any explanation. Honestly, I can't figure out what it is, what it does, or how it works. So I have removed it from the page. If someone wants to put it back, with an appropriate explanation, please do so!
[[User:DOwenWilliams|DOwenWilliams]] 07:25, 10 June 2011 (PDT) David Williams


The article mentions ancient Egypt. How did heliostats work in the days before clockwork and motors? --[[User:Chriswaterguy|Chriswaterguy]] 17:18, 8 July 2010 (UTC)
:I think I've now figured out that the image shows a simple heliostat (with a strange blue-green mirror) that is intended to be operated by hand. I wonder what the ancient Egyptians would have thought of it. They moved heliostat mirrors by hand, but they certainly didn't need anything as complicated as this device. It appears to have some sort of protractor for setting the angle of elevation of the aim direction of the mirror. I bet the Egyptians never calculated any angles, nor used any protractors! [[User:DOwenWilliams|DOwenWilliams]] 18:41, 17 June 2011 (PDT) David Williams
 
:Like I said on the main page, the mirrors were aimed by hand. Basically, the "machine" consisted just of something like an easel, on which the mirror could be placed. At frequent intervals, a person - a servant or slave - would shift the easel and mirror so it continued to reflect light in through the door of the building, or whatever.
 
:At least, that's how they still do it nowadays, to show tourists. I've been to Egypt a couple of times and seen them doing it. I assume they are using the same method as was used in ancient times. Generally, the ancients documented things well with hieroglyphic descriptions, so the methods they used are still known with relative certainty.
 
:[[User:DOwenWilliams|DOwenWilliams]] 19:08, 8 July 2010 (UTC) David Williams

Revision as of 07:19, 26 September 2011

Old technology
Latest comment: 13 years ago5 comments2 people in discussion

The article mentions ancient Egypt. How did heliostats work in the days before clockwork and motors? --Chriswaterguy 17:18, 8 July 2010 (UTC)Reply[reply]

Like I said on the main page, the mirrors were aimed by hand. Basically, the "machine" consisted just of something like an easel, on which the mirror could be placed. At frequent intervals, a person - a servant or slave - would shift the easel and mirror so it continued to reflect light in through the door of the building, or whatever.
At least, that's how they still do it nowadays, to show tourists. I've been to Egypt a couple of times and seen them doing it. I assume they are using the same method as was used in ancient times. Generally, the ancients documented things well with hieroglyphic descriptions, so the methods they used are still known with relative certainty.
DOwenWilliams 19:08, 8 July 2010 (UTC) David WilliamsReply[reply]
Thanks - wondered if it was that but I wasn't quite clear.
It's an interesting pattern, looking back in history - the very wealthy and privileged used to rely on masses of labor (servants or slaves). Even simple labor-saving devices such as wheelbarrows were not used. The Roman and Greek civilizations were surprisingly close to an industrial revolution. One major factor holding them back was that they had slaves - it was only when such labor was unavailable that there was a real impetus to develop technologies to do work. --Chriswaterguy 00:34, 21 July 2010 (UTC)Reply[reply]
In at least a few cases, the slaves have developed the technology to put an end to their own slavery. I'm thinking of what happened in about the 18th Century, in England. Water was pumped out of mines by primitive steam engines, invented by Newcomen (?sp). Children were employed (essentially enslaved) to turn valves to send steam into and out of the cylinders. One kid, I don't know his name, managed to tie bits of string to the valves and other parts of the engine, so the engine turned its own valves and the kid could relax. However, this had the unintended effect of making the engine work a lot better. The timing was improved. The owners of the mine noticed that the pump was working better than it used to, so they investigated. Finding that the kid was now redundant, they threw him out onto the street. As a slave, he had been fed. Now he had nothing.
DOwenWilliams 02:07, 21 July 2010 (UTC) David WilliamsReply[reply]
A further thought: Western science and technology were essentially stalled until the 15th Century because of the horribly cumbersome numerical representations that were used. Can you imagine calculating the area of a circle, using Roman numerals?! Only after "Arabic" numerals were introduced into Europe in the late 1400s could calculations be done accurately and easily. This led quite rapidly to the development of science in the 16th and 17th Centuries, and to the start of the Industrial Revolution in the 18th Century. The 18th Century was also when the slave trade was at its peak, which makes me doubt whether the absence of slaves causes technology to be developed. DOwenWilliams 14:09, 21 July 2010 (UTC) David WilliamsReply[reply]

AT heliostat

The AT heliostat

This image was put into the heliostat page today without any explanation. Honestly, I can't figure out what it is, what it does, or how it works. So I have removed it from the page. If someone wants to put it back, with an appropriate explanation, please do so! DOwenWilliams 07:25, 10 June 2011 (PDT) David Williams

I think I've now figured out that the image shows a simple heliostat (with a strange blue-green mirror) that is intended to be operated by hand. I wonder what the ancient Egyptians would have thought of it. They moved heliostat mirrors by hand, but they certainly didn't need anything as complicated as this device. It appears to have some sort of protractor for setting the angle of elevation of the aim direction of the mirror. I bet the Egyptians never calculated any angles, nor used any protractors! DOwenWilliams 18:41, 17 June 2011 (PDT) David Williams
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