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The
ornamental
sundial from
B&Q photographed at 1450 GMT on a sunny October afternoon. You can
see from the shadow that the sundial is showing approximately the
correct time of day. Quite impressive. Given the longitude, however, it
should have been reading around 1440 local Sun Time, but it's near
enough for an ornamental dial, and I may not have set it up quite
correctly anyway.
This
photograph shows the
gnomon (the pointer) which casts a shadow across the face of the dial
to indicate the time. The angle of the edge of the gnomon, highlighted
in red, must be the same angle as the local latitude. In this
case the latitude is approximately 53º North so the angle of the
gnomon here is also 53º. I had to adjust the angle of the
gnomon on this sundial by putting a couple of brass washers under the
front edge to lift it to the correct angle.
This
is
an experimaental paper
dial, printed off the internet from the the NASA website. This dial is
quite different from the usual dial with a horizontal face. This
one has a face which is constructed to be at the same angle as the
local latitude. This on has a face which is actually at 52º. The
style (gnomon) is made to be perpendicular to the face. The digits must
be evenly spaced arount the semicircle to give accurate time
keeping. Even though this one is only made of paper, it is very
accurate. Because the sun effectively falls on the dial from
behind it seems that there is a drawback to this design. In the winter
months when the sun is very low in the sky, it does not get high enough
to illuminate the face of the dial and therefore produce a shodow from
the gnomon. As this photograph was taken in October, I have had to draw
in an imaginary shadow! In June, however, this dial kept
excellent time.
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A
wider
view of this attractive
sundial, showing the long shadow being cast by the sun even at 2:30 PM.
This
second
paper dial is more
conventional, with a flat horizontal face. The gnomon of this sundial
is designed for latitudes of 53º North, as you can just about see
in the above photograph. The digits of this dial have been more
scientifically laid out, using some trigonometery to provide the
correct angles between the numbers and therefore provide more accurate
timekeeping.
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Hi Mike, my name is Jackie and I ran across your page http://www.mds975.co.uk/Content/sundials2.html, while doing some research. I volunteer at our local community center and do science projects with children of various ages there. Soon I will be showing them how to construct their own very basic sundials and I was looking for some electronic resources. I have found some helpful material on your page, so thank you! While I was browsing your page I noticed that you have a link on your page that says "Telling Time With Sundials" and it goes to http://www.watch-inc.com/articles/sundials.html I have used this page as well and it's a great reference material. If you are interested in adding similar content, then I thought I'd share an excellent page I have found through my own research. The link that I have goes to http://www.timecenter.com/articles/when-time-began-the-history-and-science-of-sundials/ and it's got some great info on the history and science of sundials, as well as some links for further resources. Just thought I'd pass it along :) Take care, Jackie Carson. July 2010. Thanks Jackie, I've added your link suggestion to the other pages. Mike. |
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