Author Topic: Meridian Sun line  (Read 1057 times)

Raymond Locke

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Meridian Sun line
« on: April 01, 2021, 05:21:56 PM »
The latest issue of Sky & Telescope had an article on Cassini.  I especially like his meridian sun line a cathedral  floor in Bologna, Italy. The movement of the sun marked Easter and the seasons.   I am trying to replicate that thru my lanai, unto my driveway.  It's a slow summer!

It seems to be easy, ( just drill a hole in my roof )  except that my aluminum  roof over my covered driveway is 4" thick! So to accomodate a sun angle of 86 degrees ( for summer sun) and 40 degrees ( for the winter sun), I have calculated that the hole would have to be about 8" in diameter.

That is too big.    One solution is to cut a slot in my roof ( still 8" long), oriented due south, of course.

But I am looking for a simpler way.  Is there a way to bring down to the floor a circle of light that transmits whatever angle it sees of the sun..to the floor.
   That is, sending the noon sun along a meridian ( south-north )  line .  Must go thru a 4" thick roof.

I wonder how Cassini did it thru very thick stone walls??

Anyone have any ideas?

Sean McDonald

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Re: Meridian Sun line
« Reply #1 on: April 01, 2021, 06:07:50 PM »
Raymond, you are a wild man.   I applaud your enthusiasm
 It seems to me you would need a small hole on the roof itself, and maybe a 6 inch hole on the ceiling creating a cone affect towards the small hole.  The light coming through the small hole on top would not be blocked by the surface below it, thatís probably how they worked around it in thick stone as well
  Tom Hanks did it in that movie ??? Castaway??  So you can do it too.
 Keep us posted please 👌

Raymond Locke

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Re: Meridian Sun line
« Reply #2 on: April 04, 2021, 09:42:39 AM »
Thanks.  That looks like a better answer than lenses or a solid rod.  I may use a cone shape, or just an upside down bowl with the bottom cut out and a 1-2" hole in the lanai.  Now I need to mark the floor!
Thanks  for the tip.

Raymond Locke

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Re: Meridian Sun line
« Reply #3 on: June 07, 2021, 01:11:15 PM »
Project is 1/2 complete.  I did the math for the Summer and Winter Solstices and laid out where I want the Meridian Line ( 166" long ) to run along solar noon on a true N/S line.

 After some laser positioning, I put a large (10"x 8") hole on the upper side of my 4" thick aluminum lanai roof, glassed and waterproofed it, and put a smaller hole ( 2") underneath.............which I disguised as a SUNflower.  It looks great.

Now I'm marking solar noon (using the SunCalc App), and checking to get one end of the meriridan line on the driveway perfect.  June 20th should do it.
Although I can lay out the rest of the line with a laser, I think I'll wait six months to get the Winter Solstice!

The other half of the project is the design of the meridian line.......inlay a brass strip, paint it, inlay tiles, glass baubles??  And what notations to put on it.  I could overlay a 1" x 1/8" brass strip which gives me the option of stamping dates into it...........or?  I'm open to ideas.

It would be a chore to route out a groove to make the strip flush.   I have several months think about it.  No use rushing.