Pocket Sundial

Imagine you are trekking in the wilderness and desperately need to know the current time (perhaps to determine if there are enough sunlight hours in the day for you to reach the next clean water source, or next decent place to take shelter/setup camp). Your trusty watch stopped working hours ago (smashed, water damaged, or ran out of batteries) and as you stand around thinking about it, you lose more and more of the possible walking time you still might have. Suddenly a thought hits you, and you frantically tear off your pack and dig through the contents. Searching until, there -- sitting snugly in that one, oddly shaped pocket that never seems to be the right size to store anything useful -- you find it. You had completely forgotten that you packed it, or even that you had made it for that matter. And honestly you never thought you'd ever actually need to use it. But that hand crafted, wooden pocket sundial -- that you made in your garage one day because you were bored -- might just save your life today. Your previous feelings of dread and indecision are quickly replaced by a wave of hope as you carefully align the built-in compass and discover that you are once again capable of accessing that eternal and intangible dimension of our universe.......TIME!  Or, if the sun has already set, you can burn it to keep you warm (it is made of wood after all).


Ok, that is probably not the most likely of scenarios, but a pocket sundial can actually be a fun and useful thing to have. It can tell time fairly accurately while the sun is out, and a built-in compass can be useful at any time.

This Instructable will document my experience making one for my self, and show you how to make one of your own. So, lets get started.

Step 1 Tools and Materials

Here are the necessary tools and materials for this project...

TOOLS:
    - Hacksaw (and/or band saw)
    - Compass (for making circles)
    - Scissors
    - Sandpaper (several grades between 60 and 400)
    - Dremel rotary tool

MATERIALS:
    - 2 X 4 (I am using pine)
    - Small compass (for finding North)
    - Small piece of plastic (about 3" x 3")

SAFETY EQUIPMENT:
    - Shop goggles
    - Dust mask
    - Gloves

Comments

[oompa]

This is the coolest thing I have seen in awhile! Great job!!

[Dream Dragon]

A really nice piece of work.

[Airth]

Nice sundial! These have always fascinated me, and it's nice to see someone come up with something portable and practical :)

Just a note on judging time in the outdoors, especially if you're deciding on when to set up camp...use the hand span method to estimate how much daylight you have left. To do it, hold your hand at full arm's length, palm in and thumb up, fingers together. "Rest" the lower edge of the sun on your index (pointer) finger, and "walk" your hands down to the Western horizon or mountains. Each span is about an hour, so each finger width is around 15 minutes.

[TheHawkeye]

Great idea. You wouldn't need the compass if you know that the sun rises in the East and sets in the West, but it does increase accuracy (depending on magnetic declination) and ease-of-use.

[blah12344321]

Except the sunrise and sunset are roughly east/west, but it varies everyday and is only exactly east/west on the equinoxes (or solstices?)

[BEAR GRYLLS 88]

Great!!

I don't have a dremel or anything to shape it except for my trusty knife.
how do I proceed?

[rimar2000]

Nice work!

How do yo adjust the time regarding the season and latitude?

[drumbum11]

Hey, thanks.

As far as I am aware, the only seasonal adjustment that is necessary is for daylight savings time (where applicable). The sundial will always read your local standard time (it will say noon when the sun is directly overhead), so when daylight savings is in affect, you will have to compensate by adding an hour to whatever your sundial says.

Using the sundial in different latitudes is more complicated because the value of your latitude is used in the equations for drawing the time lines and in making the gnomon. Technically a new gnomon and dial face would be needed. However, with a sundial this small, the precision is already low enough that if you are with in 10 or 20 degrees of latitude it should not affect the accuracy a whole lot. However, since it is so easy to remove the gnomon, it might not be a bad idea to make a new one to match the new latitude, which will help decrease the margin of error.

[rimar2000]

OK, now I understand, thanks!

[arpruss]

To be little bit more precise, the sundial will read local solar time. Your local standard time may be up to around half an hour off from that, depending on where you are within the time zone. You can compensate for this in your calculations, but then the sundial will only be usable at your own longitude.

[drumbum11]

Ah yes, good catch. Thank you for the clarification.

[rimar2000]

Longitude incides directly, but latitude a bit less. Anyway, you must consider it, I think.

[arpruss]

Actually, there is a way to use a sundial in a different latitude--you just tilt the sundial by the difference in latitudes.  A couple of ways to do that.  The most general might be a leg that comes out on one side, calibrated in latitude angles.  Another way might be to cut some five degree wedges, and then you can stack them.

Changing out the gnomon isn't good enough, because the formula for the angles depends on the latitude.

By the way, probably an easier way to generate the face for this wooden sundial without measuring small angles is to use the automatic generator in my papercraft sundial ible to make a pdf file, then load the pdf file into Inkscape, shrink it down, and then transfer the angles to the wood with pins.  This would also compensate for longitude (if you don't want that, set the longitude to the nominal central longitude of the time zone).

[rimar2000]

Good idea, I had not thought that. Maybe a movil (articulate) gnome too, it could help.