Yes I would say that there is something wrong with the video.
The figure-eight shaped analemma is generally attributed to Grandjean de Fouchy, a French mathematician who devised it around 1740 as a way to regulate mechanical clocks by reference to the sun. The device was called the "mean time meridian" and was laid out on an interior the floor using markers on two sides of a straight north-south noon meridian line. A spot of Sunlight was projected onto the floor thorough a ring gnomon outside the building through a window. The sun's image would cross the "mean time meridian" line at exactly noon as measured by a perfectly accurate ideal clock and could therefore be used to regulate an actual clock. The mean time meridian or analemma, therefore, was more of an invention than a discovery and is only meaningful because of the juxtaposition of mean time clocks and solar time. When a clock is connected to a camera, the same figure emerges in the sky if a photo is taken at the same time on successive days. Since the analemma (mean time meridian) was originally developed with reference to noon meridian line, it does have a logical connection to noon, but the photos of the sun that trace out the figure in the sky are generally not taken at noon. The slope of the figure is a function of latitude. Its position (higher or lower) above the horizon is a function of the time of day that the photos are taken. Morning and afternoons provide more interesting background scenery. The values of the true sun's deviation from a mean sun were actually explained and calculated by Ptolemy in the Almagest! However the graphic representation of these values that we call the analemma would probably never have arisen without the intervention of a mechanical clock. The upper and lower limbs of the analemma do correspond to the two solstices, but the crossover point when clock time deviates from solar time is not related to the equinoxes. This appears to have been a plausible (but wrong) guess by somebody. Jack Aubert From: sundial [mailto:[email protected]] On Behalf Of ruben nohuitol Sent: Monday, July 29, 2013 6:12 PM To: [email protected] Subject: Is there something wrong with this Cassiopeia video? Hi, I watched this video, <http://www.youtube.com/watch?v=IhqzW97_47w&feature=share&list=PLgLV7Kpk8Y6G DdceXQCmgDLgbYSH7TeSt> http://www.youtube.com/watch?v=IhqzW97_47w&feature=share&list=PLgLV7Kpk8Y6GD dceXQCmgDLgbYSH7TeSt , of the Cassiopeia Project, in the 2th minute says the equinox is marked for the cross point of the analemma, which I found not match with my analemma but not with others, as show in pictures anexed. Also found they say the marks are at noon, if noon means solar midday it is not true, because the marks made a meridian line, not an analemma, and if noon means 12:00 there´s no point to mention it, because you can make the mark at any hour, just taking care is the same hour. The video shows an left inclinated analemma, showing is at morning, not at noon in any case. The image of the analemma is very close to the earth in case of a real photo secuence, note the winter solstice point is very close of the earth, except the case of the picture is taken very very close of the north pole, I assume. By the way, please tell me if there´s a method which shows graphicly the equinoxes on a analemma, because I heard they need to make an analemma for exactly know when the equinox are. Thank´s -- This message has been scanned for viruses and dangerous content by <http://www.mailscanner.info/> MailScanner, and is believed to be clean. -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean.
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