Asking About Sundials

[and getting help]

Dave Hess challenged the kids to design a sundial for McMurdo. We decided to search the Internet for help. Two kind gentlemen replied...

Hi, Patti!

Sounds like a fun project, indeed. That near the pole, almost any common type of dial looks like a Polar or Equatorial Dial... There could certainly be some interesting variations for the polar region. What's the latitude and time zone at McMurdo, anyway? I'd be happy to pass on what little expertise I have for your class!

Dave Bell

Dave Hess replied to Dave Bell...

Hi Dave,

Patti forwarded this to me, so I guess I can add her as a CC to give her a few clues. McMurdo is 166E 78S, rounded off to the nearest degree. Two of the questions asked of the kids are to draw a sundial, and how to position it with a compass. Both are trick questions for the kids, to see if they can think the project through.

The point I am trying to make with the sundial is the rotation of the sun and the direction of the number placement. As to the compass, magnetic south happens to be north of us.

Thanks for you help,
Dave Hess

From the Netherlands...


That sounds great! I often wondered when this would happen. A vertical sundial wouldn't be a good idea I think, because Antartica is perfectly suited for a horizontal sundial. The style will be nearly vertical and the hourlines will be for all 24 hours on the sundial face (midsummernight sun!)

OK, I understand. It will certainly help if you can find a book about sundials in the library; not to learn but to get a feeling and see some pictures etc.

By the way, in where do you live in the USA? There is in the USA a group of sundial 'freaks' organized in the NASS (North American Sundial Society), ENDBy the way, in where do you live in the USA? There is in the USA a group of sundial 'freaks' organized in the NASS (North American Sundial Society), perhaps I can find the adres of someone in your neighbourhood.

A vertical sundial is a sundial that is mounted in a vertical position against a wall. Any wall is max. 12 hours getting sunlight. No sunlight on a sundial means no time reading from it.

A horizontal sundial is in general a horizontal plane. In both cases you need a 'style' to give you a shadow on the sundial face. If you arrange everything in such a way that this style is parallel to the earth axis it works out to be a pretty accurate time piece. One of the first things to know is the exact location on the earth where the sundial is going to be. After that we can work out a number of possibilities.

In December I visited the Antarctic Centre in Christchurch New Zealand and was impressed about everything that happens at McMurdo and under what conditions. Because those conditions I got a nice idea about a sundial for McMurdo.

The type is called 'Annalemnic Sundial' (I am not sure whether I spelled it correct in English). This type is horizontal and has always a vertical gnomon to cast a shadow. The hours markings are arranged on a ellipse. The gnomon is placed on marked spots according to the date. There is variation on this type where you use your own shadow as gnomon shadow. You just stand on marked spots according the date and you can read the time. At McMurdo the ellipse will be nearly a circle and the hour markings will be all around! So a sundial which is sturdy and easy to construct and hardly any maintenance. What time zone do they use at McMurdo? I need to know that to make sure the right hour numbers are at the right spots.

Think it over, I think you will like this! If you think this is something to work out I can do that and send you the measurements etc. Here in Holland we used this type a few times on school squares, children are enthusiastic.

Thibaud Taudin-Chabot

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Patricia A. Weeg
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