Mistakes I Made While Making a Sun Dial

by Deb on February 25, 2011

Sundial record

Well the first mistake was expecting there to be sun.  I mean it’s the desert, right?  OK, technically it’s the semi-arid zone, but right now it feels more like the ‘cyclone tail and monsoonal trough dumping ground.’  Which, I hasten to add, is way better than being the cyclone target or anything like that.  But it’s wet.  And cloudy.  And we have a mosquito plague happening.

But after will-I or won’t-I-ing for a week I did it.  And it worked, for the brief times it was sunny rather than soggy.  But next time there will be some changes.



Cardboard box as a dial plate with a plastic drumstick as a gnomon.

The basic idea worked well.  A large cardboard box gives you lots of room and is easy to draw on.  Because it’s a box rather than flat it is simple to stick something into the middle of it to stand up and it’s nice and stable.  Then all you need to do is check it periodically and mark the end of the shadow and the time, join them up and Bob’s your mother’s brother.

I even thought to put it inside a larger plastic box to protect it from the mud and mark where it went on the ground so it could be returned after the rain.  But.


Somewhere without anything large around it to block the sun.

  • I should have had a longer gnomon, the stick that casts the shadow.  I was worried about the shadows being too large and not fitting on the box but thanks to the weather it only worked in the middle of the day, making all the shadows very close together.
  • A pointy end would have been better than a knob.  I thought the knob would make it easier for kids to join up the shadows, but it was too big and got in the way.  You can see on the record at the top that they practically overlapped.

Where next?

I was surprised by how straight and central the track was – I was expecting it to be much more curved or displaced sideways.  It made me realise that it’s only a month until the equinox, and given our position in the southern tropics the sun is pretty much directly overhead for us right now. I’m going to point it out to the girls because it’s something that doesn’t happen all that often.  To be exact, it happens twice a year if you live in the tropics and never if you live outside them.

I’ll definitely be doing this again with the girls when it stops raining and we can leave it out all day.  The little one is very in to drawing at the moment and will love marking the shadows.  By putting it back in the same place and doing it at different times of the year it will be a great way to show how the sun moves, I can see that using different colours to keep track of different times of the year is going to be a lot of fun.  I found it thrilling to actually see a record of the sun moving, something we generally take for granted.  Sharing the wonder, that’s why I teach science.

I’d love to compare sundials from around the world – do one and take a photo for me!

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{ 5 comments… read them below or add one }

Cass February 25, 2011 at 7:43 am

Love it. I can’t wait until my daughter is old enough to do this sort of stuff with her.

I remember saying the same thing about twelve months ago when you wrote about light and I am happy to say we are able to do that stuff now.


rivqa February 25, 2011 at 4:42 pm

I love the word “gnomon”. Isn’t it great how I have useful things to contribute? 😉

Anyway, looks great!
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Deb February 25, 2011 at 6:09 pm

I do too, that’s why I managed to work it in a couple of times 🙂


Glowless February 27, 2011 at 9:10 pm

Wow, gnomon, really? I never knew!
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Annie February 28, 2011 at 6:19 am

oh this is very cool, I think we’ll be giving this a go this year…


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