Hi all, Sara is spot on. If you are going to teach how a sundial works you have to 1st start with the largest clock in the world, the Earth with a sundial at the poles. The moment for this clock is the Earth spinning. Then move the sundial to the Equator of the globe and show how the earth also turns the sundial at the Equator as it is geared to the Earth. But this time the sundial only works for around 1/2 the time because we now have day and night. Then move the sundial to another latitude on the globe and show how the style is kept parallel to the axis of the Earth, by adjusting the style to the latitude. To show how the hour lines are drawn, you could use a disk with hour lines marked every 15 deg as Tony has on his sundial. You extend each hour line onto the horizontal base of the sundial. A building with a vertical sundial could also be stuck onto the globe. You might also indicate that the style of all these sundials are parallel to the axis of the Earth.
To show this a world globe with a lamp as the sun could be used. And rotate the globe to show the time on the sundial. A equatorial sundial could be used as it would also work at the poles. A globe and lamp could also be used to show the seasons when the globe is moved around the sun. Your students could design and make their own cardboard sundials for different cities around the world. Then test their sundials by sticking them on the globe. The concept of using the Earth as the largest clock in the world was described in my digital add on to one of the NASS magazines. Roderick Wall. From: Schechner, Sara Sent: Wednesday, April 27, 2011 9:44 PM To: Astrovisuals ; sundial@uni-koeln.de Subject: RE: Sundials for teaching This is very nice, but it appears that it will only work during the summer half of the year between the equinoxes, because the side triangles will block the sun from the underside of the disk during the winter half. I prefer teaching sundials that are equatorial and can be compared to a globe dial for all seasons. (I use a small globe with a rod stuck up the axis and protruding at both poles, and an equatorial disk similarly mounted and adjustable for latitude.) Sara 42°21’N, 71°13’W Sara J. Schechner, Ph.D. David P. Wheatland Curator of the Collection of Historical Scientific Instruments Department of the History of Science, Harvard University Science Center 251c, 1 Oxford Street, Cambridge, MA 02138 Tel: 617-496-9542 | Fax: 617-496-5932 | sche...@fas.harvard.edu http://www.fas.harvard.edu/~hsdept/chsi.html From: sundial-boun...@uni-koeln.de [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Astrovisuals Sent: Tuesday, April 26, 2011 6:06 PM To: sundial@uni-koeln.de Subject: Sundials for teaching I would like to put my "Sun Disc" forward as a universal equatorial adjustable dial.. with lots of helpful instructions! Extra instruction sheets are available to help teaching the concepts behind sundials. Haven't reaped many rewards so far, though! http://www.astrovisuals.com.au/SunDisc.html * David Widdowson, ASTROVISUALS, * * 6 Lind St, Strathmore, 3041, AUSTRALIA * Ph/fax: 61- (0)3 - 9379 5753 * EMAIL: m...@astrovisuals.com.au WEB: http://www.astrovisuals.com.au -------------------------------------------------------------------------------- --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial -------------------------------------------------------------------------------- No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1209 / Virus Database: 1500/3599 - Release Date: 04/26/11
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