Designing a reflection sundial for the southern hemisphere

[Jadaav]

Hello,

My aim is to build a small reflecting sundial as designed by Sir Isaac Newton.

I found from a website that it consists of a ceiling and a small mirror. What I want to know is how it works, the concepts behind it and how to build one. It's for an undergraduate project that I've got.

What I've learned is that it depends on the latitude, longitude and orientation of the building.
Resource : http://interiorsundials.tripod.com

Can anybody help me ?

 

[haruspex]

Hello,

My aim is to build a small reflecting sundial as designed by Sir Isaac Newton.

I found from a website that it consists of a ceiling and a small mirror. What I want to know is how it works, the concepts behind it and how to build one. It's for an undergraduate project that I've got.

What I've learned is that it depends on the latitude, longitude and orientation of the building.
Resource : http://interiorsundials.tripod.com

Can anybody help me ?

One advantage of such a dial is that it casts a spot instead of a line. This means you could mark the ceiling so as to tell you not only the hour but the time of year.
The easiest way would be just to set up the mirror and mark the ceiling where the light falls. Of course, you don't want to do that once an hour every hour for 365 days. Anyway, the sun would not always be shining. But you could collect enough samples that you could then fill in the gaps by interpolation.
There's a bit mor information here https://en.m.wikipedia.org/wiki/Sundial#Reflection_sundials

 

[frkrygow]

I'm in the northern hemisphere, but I'm nearly done constructing such a sundial on the ceiling of my study. I'm an engineer, not an astronomer, so it's been very educational.

What I did: I placed a small chip of mirror about 10 mm x 25mm horizontally on a window ledge about a meter below the ceiling of a south facing room.

I set alarms on my watch for just before the hour and just before the half hour, all day long. (I also did 15 minutes and 45 minutes but I recommend omitting those. Too much data!) At precisely those times, I put a small sticky dot on the ceiling marked with the date and time. I repeated as often as possible (given clouds, tree shadows, etc) for about two year. I recently drew in the curves in chalk connecting each (e.g.) 11:00 dot. The result is a series of analemmas drawn on the ceiling. I've also added the straight line for the equinoxes and curves for the path of the sun's dot on the solstices.

It's about time to paint the curves permanently, which promises to be tricky. The project has taken quite a while. Let me know if you have questions.

 

[frkrygow]

I almost forgot: Here's a talk on how one woman did a similar project: