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Meridian line

Jack Martin

By Jack Martin
in Imaging - Solar

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furrysocks2

furrysocks2

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I reckon between 12:50 and 12:55 in the afternoon, assuming the paving slabs are square.

I can show my working, but don't want to spoil it for anyone else giving it a go, or mislead them.

 

Edit: fuelled by coffee, I've revised my estimate to between 12:50:20 and 12:54:27, perhaps even between 12:52:19 and 12:53:05 but maybe I'm pushing it because you appear to me to be wearing fairly loose fitting trousers. ;)

meridian time estimate.jpg

 

Edit 2: Using a slightly different final stage, I get 12:52:08... I'm going to stop now.

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furrysocks2

furrysocks2

Posted
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No maths in here as I got it wrong twice, but here's two ways of how not to do it...

First attempt:

  • assumed paving slabs were square, so drew up a grid of 1x0.5 slabs and two lines for meridian and shadow:

original traced.jpg

  • then by ignoring the non-linear pixel scale across a half slab width due to perspective, took measurements to effectively draw the meridian and shadow line as cartesian coordinates wrt the slab grid:

cartesian plot.jpg

  • then measured the angle between these lines
  • into Stellarium, set location, get sun to corresponding position in azimuth and note time.

 

Second way was using two-point perspective:

meridian working.jpg

  • find the two vanishing points for the paving slab grid
  • project the shadow line and meridian line up to a horizon line between the two vanishing points
  • draw a right-angled triangle and rotate/translate until intersecting both vanishing points and the shadow line
  • draw line from the right-angle triangle/shadow crossing point to meridian/horizon crossing point
  • measure angles and refer to Stellarium as before.

 

Both guesswork and both incorrect - very interested to know how it can be done.

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Floater

Floater

Posted
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4 minutes ago, furrysocks2 said:

How is it done, then?

Exactly.

Come on, Jack. Enough of this teasing and tantalising. 

I'm so out of my depth here but I have been following with intrigue. You wrote of 'a few days' but it's into double figures now!

So I repeat, Jack, come on ... ?

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Paul M

Paul M

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Just now, furrysocks2 said:

I didn't know that - I assume Stellarium did, though.

I don't know if Stellarium is the  best source of info but I do have a fascination for the marvellous analemma.

It can be a thing of beauty, a marvellous educational tool  or both.

A general fascination for orbital mechanics helps too :)

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Jack Martin

Jack Martin

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I have been in La Palma visiting the observatories specifically the 10.4 m Gran Telescopio Canarias.

I don't know the maths steps  I just took the photo and asked the question.

What do you get the satisfaction of solving a problem my respect and the respect of others.

Thanks to all who tackled this question.

Jack

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