Tuesday, March 22, 2011

Gardening: How to make a sundial. A project for a sunny day! (or not…)

A day without sunshine is like, you know, night. – Steve Martin

A stone sundial using a rod as a "gnomen."
I've decided on one of my first garden projects after Spring yard clean-up is over. It will give me years of enjoyment and use. I’m going to make a sundial. It’s actually not that difficult and can be a beautiful addition for your garden.

You can even use a person to cast
the shadow!
I haven’t quite decided if it will be mounted on a large granite rock (a nice garden feature) or flat stones embedded in the lawn (still a feature, and easier to cut the grass over top…). 

You can use anything weatherproof for the dial face (stone, metal, wood) that you can mark on. Ensure your sundial is installed in a shadeless spot or some hours it won't cast a shadow. It can be mounted to stone, a plinth, a wooden stake—you name it, as long as it's sturdy and unmoveable.

You can even make a sundial that uses your body to cast the time shadow and stones in the lawn for the hour markers (at left). Grooooovy!

Sundials have been around since ancient times, most probably due to the discovery that the shadow of an upright stick tracked with the sun as the day progressed. It was the beginnings of measured time.

As time was subdivided into hours and then minutes, the dial divisions became finer and one could, depending on knowing their latitude, be fairly certain what hour and minutes of the day it was where they were. Latitude is an angle measured in degrees (°), marked by horizontal imaginary bands that run parallel to the equator and end at the north and south poles. 

The gnomen on this bronze dial is
a traditional shape.
The equator is 0°, the poles 90°. Halifax sits at 44° 39'. Stewiacke, Nova Scotia is 45°, exactly midway between the equator and the north pole.

It's actually not difficult to create a sundial. There are two basic methods. One is easy but takes a day; the other is faster but requires a protractor, or print out the one I have supplied at the bottom of this post.

You also need a flat surface to mark out your hours, and a vertical upright gnomen (hand) to cast the shadow. The gnomen can be any shape as long as it casts a straight narrow shadow that reaches your hour marks clearly. It's most usually a decoratively cut triangle. It can also be a rod like the image at the start of this post.

Securely connect the gnomon to the dial face at dead centre. The angle of the gnomon relative to the face of the disk should equal your latitude. (Halifax 44° 39', or as close as you can get.) 

There is a link below that will give you the latitude of where you live anywhere on Earth for your specific angle. Use a protractor to ensure the gnomon is cut, or mounted, at the correct angle. (See the bronze dial picture for a clearer understanding).


This is the resulting chart for Halifax from
link no. 2. Any city can be done using both
links. Click to enlarge.
The simple, yet slow way:
If using a face with mounted gnomen (instead of a lawn sundial), angle it to your latitude (i.e., Halifax is 44° 39'). Whatever style of sundial you're making, the initial shadow cast "hour" has to agree with whatever's on your (correct) watch. For example, if you start marking at 9am, then that's where you mark the 9am shadow on your dial. 

Mark where the shadow is every hour. Remember to keep the sundial and gnomen stationery—facing the exact same direction—so the hour marks will be accurate. Any early hours can be calculated by mirroring where they fall in the afternoon/evening. 8am is like 4pm, 7am is like 5pm, etc.


The hard(er) way, although not too hard:
This one allows you to make a sundial regardless if it's sunny outside or not, because you can do it inside! You need a protractor, which I have supplied as a paper printout at the bottom of this post. First you need to find out where you are on the face of the Earth, then what degrees designate the correct hours. There's two sites to help you get the exact data you need. Both are completely free.

1. Find your latitude (or that of a close metropolitan area) at:
This gives you the information (in degrees, hour and minutes) of where you are. You then take that information to the next site to get a chart which lists the degrees (on a protractor) where you need to make your marks on the sundial face. Easy, right?

2. Find out your hour degrees to mark the sundial face:
Take your latitude from the first link and enter it at the link above. A chart like the yellow one you see will be automatically generated for you. This gives the degrees that you need to mark on the sundial face.

As above, insert your gnomen in the centre of the dial and angle it so that it reflects your longitude (i.e., Halifax 44° 39'). Simply mark the degrees from 0° in both directions according to the degrees you have been given in the chart.

Take your sundial outside and point the gnomon on your dial due north. Get out your compass. You may think you know but you're probably wrong. I was. The resulting shadow will fall along the appropriate hour line.

I drew this protractor so you can save and print it. Click to enlarge and then right click
to save it to your desktop. It's 150 dpi at about 7" (18 cm) wide.

One note, because you can't force people to bend at the correct latitude angle for the lawn variety of sundial, it will be slightly less accurate. Or can you…

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