Not a sundial - a shadow dial is what I want

[DaveC426913]

TL;DR

I want to track what the sun does to shadows on my property over the course of the day/year.

We have little shade but plenty of wind on my property. The upshot of this is that I have to be judicious in how/where I put up shade-creating barriers in various places around my property to maximise shade without unduly large windage.

My property is an irregular polygon and not aligned with the cardinal axes, so it is not easy to tell where the shade will be at a given time. For example, I have put up an umbrella next to our pool, but it can only shade the southish-side of the pool, and only during certain hours.

I'm sure I'm not the first one to want to know such factors. Thought I'd check what work has been done before building my own device.

I figure it's as simple as a pole about 3-6 feet high, with placed markings on the ground at appropriate times of the day by season. I expect the pole to trace out hypebolic lines across the target area (which can, in principle, range all the way from on side of the property to the other, from sunrise to sunset).

I'm trying to look up these patterns but I'm not sure what to call them.

 

[DaveE]

Maybe something like these apps. I'm sure there's many others, I just saw these first.
https://shademap.app/
https://app.shadowmap.org/

 

[DaveC426913]

Yeah but I'm looking for a gadget that I can put my backyard. A sundial but shows me inclination and direction, rather than time.

 

[berkeman]

Do you have a WiFi camera? My wife has one watching watching our backyard for the birds and animal activity...

 

[Baluncore]

Yeah but I'm looking for a gadget that I can put my backyard. A sundial but shows me inclination and direction, rather than time.

I think you need a stick with a ball on the end, that will cast a shadow on the ground or a wall. Once you start using that to map the Sun's position you will realise it is quicker and easier to calculate it.

The analemma will give you the elevation of the Sun at midday on any day of the year. You are not interested in the distance from your time zone meridian, or the equation of time, only the elevation.

https://en.wikipedia.org/wiki/Analemma#As_seen_from_Earth
https://en.wikipedia.org/wiki/Analemmatic_sundial
https://en.wikipedia.org/wiki/Equation_of_time#Notation

 

[Baluncore]

Tall deciduous trees like poplars, to your SE, South and SW, will allow the sunlight to pass during winter, but block the heat of the Sun in summer. Once the trees have gained sufficient height, remove the lower branches to allow the winter sunlight to reach the garden.

An evergreen tree canopy overhead, will keep you and your garden warmer in winter, as it reduces exposure to clear sky, typically –40°, overhead at night, when the frost is deepest. Remove the lower-hanging branches on the South side, to allow the winter sunlight to reach the garden and windows of the house.

A screen of shade-cloth, where each strip is at an angle like a louvre, can be used to allow full winter sunlight, while blocking the heat in summer. If you make the louvre from solar panels, you will get no electrical energy in winter, but sufficient to run the A/C in summer.

 

[DaveC426913]

Tall deciduous trees like poplars, to your SE, South and SW, will allow the sunlight to pass during winter, but block the heat of the Sun in summer. Once the trees have gained sufficient height, remove the lower branches to allow the winter sunlight to reach the garden.

An evergreen tree canopy overhead, will keep you and your garden warmer in winter, as it reduces exposure to clear sky, typically –40°, overhead at night, when the frost is deepest. Remove the lower-hanging branches on the South side, to allow the winter sunlight to reach the garden and windows of the house.

A screen of shade-cloth, where each strip is at an angle like a louvre, can be used to allow full winter sunlight, while blocking the heat in summer. If you make the louvre from solar panels, you will get no electrical energy in winter, but sufficient to run the A/C in summer.

I should probably have specified that I'd like to implement shading in my yard sometime before my toddler grandchildren graduate high school...

 

[sophiecentaur]

TL;DR Summary: I want to track what the sun does to shadows on my property over the course of the day/year.

without unduly large windage.

I'm about to bash on about defining the required function of this structure in detail before deciding on how to do the job. You need to say what sort of area of shade you will be needing. That will be the area that's needed for your shade-generator. Several metres square, I imagine, and it would need to move around on a Solar axis at solar rate for (I guess) six hours or more. It would work in the same way that the equatorial mount works for pointing a telescope in a constant declination. The Sun would sit nearly right in the centre of your shadow for all times of the year No need to compensate for any other irregularity if you use Solar Tracking with just one motor.

That takes care of the principle; now comes the hard bit. Your drive / mount needs to be strong enough to handle significant forces from the wind. Alternatively you could measure the wind speed and furl any shade when the wind becomes a problem. (Aamof, I recently moved into a house which had an electric sun-blind and which used an automatic procedure, controlled by an anemometer which caused the blind to furl in appropriate wind speeds. A fearsome thing which I removed asap!!)

You could have a different approach. A fixed shade and a railway which supported a motorised seat / lounger which chased the shade. Better still, the rail could tilt to achieve the equatorial mount. You could offer viewings for the neighbours and issue tickets . . . . . .

 

[DaveC426913]

My idea of a solution is a stick on a board:

It's technically a sundial but the focus is as much on the distance (magenta) as it is on the hour-angle.


If I place an umbrella or tent on my property, the part that's in the shade shifts dramatically over the day. If we are mostly outside in late afternoon, it would be folly to place a picnic table or sandbox at A; it would be better placed at B.

(The corollary, of course, is: given a fixed structure like a sandbox, where should I plant an umbrella so it casts its shade appropriately?)


Notice, by the way, that by 4 or 5 in the afternoon, the shade is very far away from the umbrella, and it hasn't moved in a straight line throughout the day.

Also, unlike a sundial, it would not be aligned with noon at the centreline. I would align the device with my primary property lines, since that's the most useful to me, and noon would be marked wherever it falls.


(Though I have included winter solstice and ... equinoces? ... I am less concerned about winter and equinox - it's not like I need to worry about shade in the colder weather; they are only on the shadow-dial for completeness).


I could build it this way, but I'm just sure I'm not the first one to define this problem.

 

[sophiecentaur]

My idea of a solution is a stick on a board:

That's a solution for finding out some of the design information. But that won't provide shade where it's needed at any time. I feel what's needed is the inverse answer. You need to 'move the stick' in order to get a shadow on the favourite lounging spot.

(The corollary, of course, is: given a fixed structure like a sandbox, where should I plant an umbrella so it casts its shade appropriately?)

I have realised that directing light to a particular place is a lot easier than directing shade. There was a thread about this a while back from someone with a shady garden and bright sunlight. It would be great to produce a steerable shadow mirror.

 

[DaveC426913]

That's a solution for finding out some of the design information. But that won't provide shade where it's needed at any time. I feel what's needed is the inverse answer. You need to 'move the stick' in order to get a shadow on the favourite lounging spot.

Good point. Yes, it would be a two-step process.

First step will be to figure out what the sun does on my property over time. Then I'll make a little map of my property and apply the geometry to it.

I could combine the two, and make the board in the shape of my property, but yes I'd still have to have a way to move the stick/ball around.

 

[sophiecentaur]

yes I'd still have to have a way to move the stick/ball around.

How big do you want the shadow? Size needed would be inversely related to how often you want to make the effort of change the screen position.
The options for design are endless. For instance you could have two posts / masts along one side of the garden with two lines strung between and a pulley system to move then West-East with the time of day. Easy to reef the sail in adverse weather. Do you think the idea would fly? (sorry)
A fine mesh would have less windage yet provide attenuation.

You have got me going; I am actually seeing this in my mind's eye in my garden. This is quite ridiculous for my application as two places are available for sitting and a sun umbrella is easy to shift once or twice. Also the neighbours would talk!!