How can I make a rudimentary sunspotter?

Question

This is similar to my Physics.SE question Microtops sunphotometer sun target optics - there I was asking about the optics principles (the answer is no good for my understanding, but I have been able to figure it out myself).

The purpose behind a sunspotter is to show when a device is lined up in direct view of the sun - vital for fields such as sunphotometry etc.

This question is given that I now understand the optics principles involved (similar to a magnifying glass, but smaller and does not burn when focused) - what method can be used to make a rudimentary sunspotter?

In particular, I am interested in:

• a suitable material that would be used for the sun target (as per the Microtops picture on the linked page).
• the same orientation of the sun target being perpendicular to the incident light.

What I am not interested in:

• any device how to make a device that allows viewing of things like eclipses.

Answer 1

I you look up sunspotter on the internet you get many things that look like this.

While this appears to do precisely what you say you don't want, i.e. imaging the sun whith a bit of calibration it could also be used to determine alignment. Effectively this is just a folded up telescope. You could align it by firing a light source perpendicular to the lens, a laser pointer would probably work well here, and marking a cross where it forms an image. If the sun image is centred on the same point then it is also aligned.

You could achieve the same thing with a standard telescope or one side of a pair of binoculars and some rig to hold the viewing screen in the correct position as you rotate.

To answer your other question the sun target in the microtops picture is just a lens to collect the light.

You could also do it something like this. Just use a long stick or pole and find where the shadow disappears. Then use a plumb line and protractor to get the angle.

Answer 2

Two points make a line, so a long tube with a photodiode on the bottom should be able to find the sun... (assuming no clouds.) In regards to Solar Photometry I think Forrest Mims is making photometers from the wavelength response of different LEDS.. using LEDs as detectors.

Answer 3

You have two options: pass light through a circular aperture or (inversely) block light with a circular mask. Either way, you create edge shadows without focusing the light. Light sensors centered the edge of the shadow (on both axes) will balance when the device is properly aligned. If the distance from the aperture to the sensors is less than the aperture diameter, the device will tell you which way to rotate to achieve alignment (balance) even for very large error angles. You may need diffusers over the aperture or sensors to soften the transition from light to dark.

Answer 4

Try this experiment:

Setup:

Carefully stab a cocktail stick into a grape at one end (longways so that the grape looks round when you look at it end-on and the cocktail stick is central). Stab the other end of the stick into a cube of cheese (slightly bigger than the grape). Now balance the stick on the cheese so that the grape is vertically above the cheese.

Procedure:

Wait until night or otherwise darken the room. Grab an LED torch and turn off the lights, hold the torch high above the grape pointing downwards. Look at the circular shadow of the grape on the cheese, when it is central around the stick it means the light is directly overhead (or at least aligned with the stick - if the stick isn't completely vertical).

Now, imagine where light sensors would need to be placed on the surface of the cheese and around the outside (beyond the shadowed area) in order to know when the equipment is lined up with the light source. Once you get it, reward yourself by eating the grape and cheese.