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Vertical declining sundial

furrysocks2

By furrysocks2
in DIY Astronomer

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furrysocks2

furrysocks2

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Something for the garden, the intention being to fabricate something in metal - this thread for recording progress.

 

Starting with a prototype...

Quote

Preliminary Measurements

Before the vertical dial can be calculated, we need to know if the wall or surface intended for mounting the dial is direct south facing, and if not by what angle it is rotated from south facing.

A simple test dial can be made as shown that has a stick gnomon mounted perpendicular to the dial face with a vertical line projecting down from the center line of the gnomon. If the shadow from the gnomon is in line with the vertical line, the sun must be directly opposite the dial.

Source: http://www.pandy.me.uk/sundials/wd_calc.htm

 

When the sun was directly opposite the dial, it was approximately 12:53 GMT. My longitude is approximately 13' W and the equation of time is approximately 3' (sundial slow). Not quite getting my head around why, but 0h53' - 13' + (-3') = 0h37' (or 9.25 degrees).

Stellarium gives the declination of the sun today as approx 5.88 degrees, and my latitude is approximately 56.25 degrees.

Following example 3 from the link above and plugging into the calculator, I get approximately 12 degrees azimuth from south (confirmed in Stellarium), giving gnomon side angles on the west and east faces as 102 and 88 degrees, respectively. Running these two figures through the calculator, I get the following results:

58e3b0a52361d_sundialresults.png.a9636560dda1b3fac9e329b86691e96e.png

Ignoring the lengths and drawing the angles FCG out on a board, I get:

my_photo-1.jpg.cd621153732433b4eb657ee0608f5d0f.jpg

I cut off the bottom corner and made a 32.9 degree ACD gnomus, the yellow one to stick out from the face at 90 degrees, but rotated by 9.25 degrees to point south, I think... and hot glued it on.

my_photo-2.jpg.01493179356594d4e3d7f9142cdb5ae9.jpg

Looking again at the calculator results, it should have perhaps been rotated by 7.9 degrees, not 9.25, the 1pm line being at 8.4 degrees.

Unfortunately, the sun's gone in and I don't know if I'll get to test it today. Next weekend, April 15th, the equation of time is 0, so if I've built it correctly, it should read correctly.

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SilverAstro

SilverAstro

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7 hours ago, furrysocks2 said:

: http://www.pandy.me.uk/sundials/wd_calc.htm

Unfortunately, the sun's gone in

I'm not surprised ! announcing your intention, for all the cloudGods to see, to build a sundial is assured to put the mockers on seeing the sun for the next few weeks !

Thanks for the link, interesting.

There is a simpler way of doing it if it is for the garden = dont mount it on yon wall, free-stand it and make it a 'Direct' :) ! or, similar, mount it on a sub-plate ;)

Of interest to astronomers of the dark-hours, mark your dial in (modified) Italian hours, then it will tell you how many hours there are to go until sunset :D

 

 

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furrysocks2

furrysocks2

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Aye well, it can't shine all the time.

It's quite a small garden and the kids need to run so can't afford the footprint/obstacle. It's fairly well shaded low down but the garage gable is south-ish facing, so it's got to be wall mounted. Anyway, I don't like the sound of "simpler". ;)

 

Hours to sunset would be amazing! I never even imagined that was a thing - will have to have a dig, hope it works vertically.

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furrysocks2

furrysocks2

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19 minutes ago, SilverAstro said:

Of interest to astronomers of the dark-hours, mark your dial in (modified) Italian hours, then it will tell you how many hours there are to go until sunset :D

 

6 minutes ago, furrysocks2 said:

Hours to sunset would be amazing! I never even imagined that was a thing - will have to have a dig, hope it works vertically.

Yes, vertical works - don't expect this, though... https://www.youtube.com/watch?v=8cNz7PyS04w - wow!

 

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SilverAstro

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17 minutes ago, furrysocks2 said:

 but the garage gable is south-ish facing, so it's got to be wall mounted. furrenuff !

Anyway, I don't like the sound of "simpler". Agreed :)

it works vertically. It does, vert, horiz, declining whatever, just a variation on dial-furniture.

It was brought to attention ( resurrected from the ancients/antiquity ) by Mac Ogilvy (sp?) on the sundial mailing list 20more y ago after he built one such at an airfield in ummm nw america ? ( somewhere where fliers needed to pay special attention to hills and sunsets! caused great interest/amusement ) cant find his web archive :( with his QBasic implimentation !!

Nice 'tube, but non the wiser for principles.

 

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SilverAstro

SilverAstro

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Dont tell the solar observsers this, but there is also a similar set of lines that can be inscribed (Babylonian) to tell how many hours have elapsed since sunrise :D so how many hours they have missed ;) The beauty is that the lines do not need knowledge of civil time etc.! (they just show the hours till local sunset ( or from local sunrise) )

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furrysocks2

furrysocks2

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24 minutes ago, SilverAstro said:

It was brought to attention ( resurrected from the ancients/antiquity ) by Mac Ogilvy (sp?) on the sundial mailing list 20more y ago after he built one such at an airfield in ummm nw america ? ( somewhere where fliers needed to pay special attention to hills and sunsets! caused great interest/amusement ) cant find his web archive :( with his QBasic implimentation !!

http://www.mysundial.ca/tsp/hours_before_sunset_sundial.html

http://www.mysundial.ca/files/H2SSManual040801.pdf

 

11 minutes ago, SilverAstro said:

The beauty is that the lines do not need knowledge of civil time etc.! (they just show the hours till local sunset ( or from local sunrise) )

Yeah, that occurred to me - I like that.

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furrysocks2

furrysocks2

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6 hours ago, furrysocks2 said:

http://www.mysundial.ca/files/H2SSManual040801.pdf

Love the graphs he's typeset in fixed width font - looks like given the original, you'd first have to print out then join the dots according to his instructions - absolute genius!!

Like his warning near the top, too...

Quote

*** Warning *** Dialing, the involvement with the history, art, and science of sundials, is very intriguing and rewarding, and the reader may find that a little dabbling with sundials leads to a life-long interest.

 

I wasn't intending on doing an hours-to-sunset dial but I can't not, now. ;) Also, watching the early sun this morning, I need one on the shed for hours to noon and the garage for the middle part of the day - don't think I actually have a line of sight for sunset itself at any time of the year, but nice ideas to play around with.

 

I don't think I can test my prototype until about quarter to ten this morning... hope the sun stays out.

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furrysocks2

furrysocks2

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Aye...

17 hours ago, furrysocks2 said:

When the sun was directly opposite the dial, it was approximately 12:53 GMT.

...

... ACD gnomus, the yellow one to stick out from the face at 90 degrees, but rotated by 9.25 degrees to point south, I think... and hot glued it on.

...

Looking again at the calculator results, it should have perhaps been rotated by 7.9 degrees, not 9.25, the 1pm line being at 8.4 degrees.

Right enough I think - if the gnomon is to cast a vertical shadow when the sun is opposite (equation of time today is 2m37s slow and longitude 13'W), then it should be just to the west of the 1pm line, not just to the right.

 

I'll see if I can get an error curve if the sun stays out today...

20170405_0902.jpg.96155d8f4e87f0d5a1cbb317e3f22cad.jpg

 

 

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furrysocks2

furrysocks2

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44 minutes ago, Starlight 1 said:

I have been marking the ground every 30 mins  and  get  Sun all day just got to check on before 9.30 Am  . So I will be making one .  Good post thanks.

Cloudy through to lunch, then I went fishing with my son and the sun came out. Not too bad, really. ;)

 

Edit: I've never made a sundial before - or even knew how to find north or south without a compass or the pole star. Sundials may be "ancient technology" but with sound maths behind it all and all manner of possibilities for getting a handle on local time through the seasons and captivating the eye, I can see why many folk get drawn in. I've ordered that book by Waugh I linked - all good fun!

Good luck with yours, too!

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furrysocks2

furrysocks2

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1 minute ago, Starlight 1 said:

Just checking marks and its got to  go on the South side of shed to get the Sun  , So if I made a flat one  I  can put it just about any were down the South side of the garden.

I think then, the angle of the gnomon is determined only by latitude, the plate/markings will be symmetrical and you polar align it (ie rotate it to point north) - is that about right?

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Starlight 1

Starlight 1

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37 minutes ago, furrysocks2 said:

I think then, the angle of the gnomon is determined only by latitude

the Sun not in the same place every day at the same time  , so I am to work out this one as well   HORIZONTAL SUNDIAL SHADOW ANGLE CALCULATOR

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SilverAstro

SilverAstro

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1 hour ago, furrysocks2 said:

I was going to correct you and say C++, but given the maturity and widespread use of astropy, you may be right after all. :D

:D:thumbsup:

That reminds me, way back I did it in Javascript and put it in a webpage so that a visitor could put in his various params and get a table of coordinates to draw the lines on graph paper to then transcribe : I wonder if I still have it buried on a disk somewhere ( or I wonder if I still have the hardware to read the disk if I can find it !! :eek:  )

said Mac "  *** Warning *** ,,,,  a little dabbling with sundials leads to a life-long interest. " But at least dabbling in it wont damage your wealth as much as other hobbies can ! :)

good luck, watching with interest.

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Starlight 1

Starlight 1

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22 hours ago, Starlight 1 said:

HORIZONTAL

This my best way with test today are give me from center of garden 9AM till 6.30PM  , at 12 it do look a bit out from the  north Stars, I  check this to night , the Sun is moving about 60mm to the  hour.

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furrysocks2

furrysocks2

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Yesterday, I was in the garden cutting some 45-odd degree angles in some 8x4 sleepers - was beyond the limits of the chop saw so was having to cut, flip it over, cut again and then finish by hand.

At some point, I thought I could see through the cut but knew it shouldn't have been all the way through yet. Turns out, the sun was aligned such that the bottom of the cut was illuminated, the sunlight passing obliquely but perfectly down the saw kerf. What were the chances..?! I like little things like that, makes you appreciate things a bit more.

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