If a mirror revolves on equatorial mount at 7.5 degrees per hour will it cast the light of the sun in the same direction all day?
This is a very low tech experiment so that I can better understand heliostats.
I do this experiment because of my lack of understanding of heliostats, because of an answer on wikipedia i did not understand and because of a big arguement about heliostats on instructables last year.
Also, there is very little information on the net about how mechanically powered heliostats work.
They were common use over a hundred years ago.
It is snowing today march 9 (usually they have a flower count here in early February!) so this gives me time to put this instructable on as requested.
Step 1: Materials and Tools
Parts of the device The device was made from a
a tightner for a a clothesline
a crocodile clip
a piece of tie wire
and a protractor picture that I downloaded from the internet
You need a bench drill to drill holes straight into wood at right angles to the surface.
A hand drill is probably not accurate enough.
Screwdriver is also needed.
Step 2: HELP! It Is Snowing. I Cannot Do the Experiment! Can You?
I cannot do the experiment. I tried it yesterday for a couple of hours and it seemed to work.
but today it is snowing and I have a backlog of work that I must attend to.
Usually we count flowers in early February to annoy the rest of Canada but this year, the weather gods decided to delay the count and my experiment too!
Do not exactly make the same thing as I did. The critical things are level foot and the angle of the hole that the rotating bit goes into. The angle must be the same AS YOUR LATITUDE. (So not 50 degrees unless you live at 50 degrees north or south) . AND if you live in the southern hemisphere, you gotta point at the south pole not the north pole. And it is geographical poles not magnetic poles!
To do the experiment, you put the foot on a flat level surface facing north south.
Then you adjust the mirror so that it shines on the spot you want. A shaded area so you can better see it. Then set up the crocodile clip at a suitable place.
Next, every hour, come back, rotate by the desired amount. 7.5 degrees per hour.
Does the reflection stay in the same place with the rotation?
Record your results and get back to us!
Step 3: Results (little Ones From 10th March)
Results can be posted as comments on this page.
My results so far seem to show that it might work!
Because I go to work early in the morning and come back late at night, I cannot get more than tiny snippets of experiments going.
One thing I noticed is that the reflection does seem to stay in the same place except it goes up and down on a vertical line.
So perhaps I am a little off on my equatorial axis or maybe (more likely) the 24 hour rotation of the sun round the axis must be alligned some way with the 48 hour rotation of the mirror.
I (or an animal) could have bumped the mirror as an alternative explanation.
Or maybe it will just not work at all!
If you want to find out, before I do, you know what to do!
This is a very cheap experiment.
I suggest mounting the mirror on a ball and socket joint right on top of the bolt going into the wood.
I tried to do this but the ball and socket I used (from an old shower attachment) was cracked.
Step 4: Links, Further Reading and "if It Works, What Next?"
Links and further reading.
http://physics.kenyon.edu/EarlyApparatus/Optics/Heliostat/Heliostat.html a bunch of pictures of heliostats from the 19th century!
And thats about it!
It seems that everybody is selling something so it is very frustrating to find detailed information on how they actually work!
Hence the experiment, I guess.
An answer from wikipedia to an earlier question by me can be found at:
If this instructable is ever any use to anyone, we can thank that answer and rimar2000 who gave me a similar answer.
If this form of heliostat actually does work, I think it is likely one clock based dripper tracker could control 5 or 6 mirrors at one time. That would mean that all you need in the form of electronics is a fairly sturdy clock mechanism to drop the dripper pipe down at a constant speed and a little pump to return the water to the top containers at the end of each day. I imagine, say, 5 mirrors with their top and bottom containers with floats in them. All the top containers are connected so all have the same water level. All the top containers are also connected so they too are at one height. One drip pipe that is slowly descending drops the top water level while raising the bottom water level thus turning all the mirrors at once.
A combination of the first and 3rd diagrams at the following link:
(Another guy did the graphics for the first diagram so imagine his graphics on the 3rd diagram (and a second container with a float in it too) and you have the picture!
They have some of my awful video further down the page, if you want to test your endurance.
Step 5: Why the 48 Hour Rotation? Theory (making It Up As We Go Along)
As you know the earth rotates in relation to the sun in 24 hours.
So why is this heliostat thing set for 48 hour rotation?
REASON 1. is fairly easy. When the mirror is set up, it is at right angles to a point that bisects the angle sun-mirror-reflection. The reflection must not move (hopefully) so if the sun moves 2 degrees round the equatorial axis , the mirror must move 1 degree round that axis to keep agreeing with the bisect rule.
REASON 2. came to me on the bus. My reflector is to one side of the axis. But imagine a big virtual mirror. It is going to be at both sides of the axis. Now, imagine it rotating. What happens? One part of that rotating mirror is going to move TOWARDS the sun at the same time as the other part of it is moving AWAY from the sun. But it is the same mirror! One 24 hour applys to one half of the mirror and the other 24 hr applies to the other half.
(I know, it sounds like bs and maybe it is!)
Step 6: Experiments Magnetic North and Ideas for Further Progress.
I have started experiments on several days now with this and they were pretty brainless ones.
I guesstimated north and thought I could fine tune it later. But i did not get enough results to establish anything. EXCEPT, time to make the experiments better.
Here are a couple of ideas. I put my device on a concrete cap of a wall which is very flat, but the wood is a bit warped. So I use a bubble level to keep it level. Also, I looked the deinclination. for victoria it is about 20 degrees east of true north. And I found my compass and used it to aim the heliostat better.
My idea of north was way off!
Before I realized that, I started to tabulated time and degrees for shining the mirror reflection of the sun in various directions in my back yard. Just turning on the axis with no change to mirror tilt.
That would keep my busy
I also drew a curve across a wall with chalk so that i could see how the curve changes as the sun moves across the sky. Just moving the heliostat in its axis without changing the mirror tilt.
Step 7: Heliostat Model on Celistial Sphere Indoors!
The celestial sphere and modeling the sun on it indoors.
Basically the earth is like a huge gyroscope in space. And just like a gyroscope, as it spins it always points in the same direction. (It has no wobble that anyone can notice in their lifetimes).
Its axis of spin is not aligned with its orbit so we get seasons.
So why not model the heliostat by using the celestial sphere idea? We need a pole as an axis, and we need something that spins around the pole (to be the sun) and another thing to spin round the pole (to be the heliostat) and something else stationary to be the target.
We also need something to measure the angles like the protractor that i downloaded.
Thats as far as I got