GNOMONICS - sundials & shadows etc,etc,

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GNOMONICS - sundials & shadows etc,etc,

Postby newgroundrodney » June 21st, 2018, 7:32 am

Other than football, one of the things I enjoy is gnomonics, making sundials and studying shadows.
As it says in The Quran, in Section 81 : "when the sun is overthrown".... well this year, out my garden it's my sunDIAL that's overthrown. Fallen over on it's side. My son stood it back up but he's positioned it in completely the wrong alignment. As luck would have it, I never had long to wait 'til 21st June, which is today, and which is the best day for positioning a sundial.
The pointy part of a sundial is called the gnomon, and the angle at which it's set, should be the same as the number of degrees of latitude.
Solar mid day occurs when the sun's shadow in relation to the object height appears at its shortest. Indeed, there's a rule I frequently quote that goes: "wherever you are in the world, be careful if you sunbathe when your shadow is shorter than you"... a rule I've always observed. People can very easily misjudge how damaging the sun's rays can be. This warning is often seen in the tiny small print on a holiday's T&Cs under advice to travellers.
Twice a day, we have the situation wherein the sun's shadow is exactly equal to the object height. (Interestingly, the Islamic religion uses this, in part, to calculate the time of their afternoon prayers, what they call "Asr"... but I digress... ) This is what I refer to as "parity".... when travelling abroad, like Tenerife for example, I like to know the times between which parity occurs. When holidaying, usually first day I will visit the beach to determine the length of the shadow, the times of parity, and the time of solar mid-day, which can differ from the time on one's watch. It's my assertion that the clocks in Tenerife (although following UK time) are often 2-and-a-half hours fast when comparing the actual time of the solar mid-day.
The time of our local solar mid-day in Cardiff is around 13:16, and frequently, as today, I like to stay around the garden, measuring shadows, wearing a watch that's 1hr 16 mins slow.... "what's the time in your world?" my son often asks!

Having an interest in these things affects other areas of life, like football and watching movies. If visiting an unfamiliar football ground, one of the first things I'll find out is which direction the pitch is aligned. When watching especially old movies, I can see by the shadows how long a particular scene took to shoot, because often the shadows will have moved considerably, even though the actors are meant to be having the same conversation.....but the shadow has moved from there, to THERE! so I rarely watch movies. Kind of spoils the continuity a bit.
Some people go to watch the sun rise but I've never seen any fascination in that. For me, it's not the sun rise that matters, but the time of solar mid-day.....that's what I observe, and that's what I'll use to fix my sundial.

I know what you're thinking : "yeah yeah, all very good, but honestly, could you BE more boring?"..... :grin:

Have a wonderful 21st June however you do it.
Thanks for reading,
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Peoples Republic of Malpas

Re: GNOMONICS - sundials & shadows etc,etc,

Postby lowandhard » June 21st, 2018, 6:56 pm

Not boring at all mate, all good stuff. I don’t possess a sundial, an often redundant accessory in this part of the world but I do admit to always carrying a compass of at least one type. I have one in my summerhouse and a weathervane to note wind direction and force. When on the road I carry a military compass ( just in case :grin: ) in my campervan. Nicely nuts, of course i am.

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