I was experimenting with this concept of using a 24 hour clock in conjunction with a parabolic mirror (inverted) to determine astronomic north. It was my attempt to better understand the use and function of the solar compass, which has to take into account the latitude, declination, and hour angles, in order to determine astronomical north. My though was that by rotating the frame of the clock until the image of the sun falls on the hour hand (see small image of sun on hour hand in pic) then true north could be determined by the orientation of the cardinal directions of the clock face. I did end up making a wooden tray which could be adjusted by tilting the whole clock to match the latitude.
This is more along the line of .....
the old Boy Scout trick of pointing the hour hand of your watch at the sun. Half way between the hour hand and 12 is South. Now don't get too picky about local apparent time and DST, but it will get you in the general direction.
The idea behind the solar compass (or any other solar instrument) is to mechanically solve the PZS triangle. Perhaps one of the earliest analog computers.
This is more along the line of .....
The idea of the solar compass is very appealing, and with miniaturization along with computation should be possible to incorporate on the top of a total station.
see article about a solar compass chip.
http://www.isa.org/journals/intech/solarcompass.pdf
To put the shadow on the hour hand you need a 24 hour clock with noon at the top, i.e. upside down in the Northern hemisphere. That is the only thing that works properly upside up down under. There is no need to turn a 12 hour clock face upside down, but you need to split the difference between 12 and the hour hand.
That is one of several Boy Scout shadow methods used to determine north. The second requires 3 sticks, put the biggest in the ground plumb and place a second one where the end of the shadow is in the morning. Use the third stick to scratch out an arc on the shadow side from the stick. The shadow will get shorter in the morning. In the afternoon as the shadow gets longer you want to place the third stick in the ground as the shadow tip crosses the circle. Half way between the 2 smaller sticks is North. Yes, you are there all day, but remember you are lost and the first day you should not move and let the rescuers come to you.
Paul in PA
The clock in the pic was one a took from my office and swapped out the motion for a 24 hour motion I got from KlocKit.
Finding North with a watch (Boy Scout Manual)
There's really a wealth of info in there. It's within arms reach of my keyboard.
(You know....Be Prepared)
