LUNAR DIAL - rotatable polar dial plate |
I have been asked by many people, especially when I have a booth at a fair, "that's nice, but how do you tell the time at night?" I am in no way an expert on the moon, however this dial works well. It is presented with no guarantees, for the, er, lunatic fringe. It is scientifically designed however it is "empirically" set on the moon's first quarter, and thus this considers longitude as well as the fact that 1q moon for the dial is probably not "the actual 1q moon" because first quarter happens over a longitude and latitude, and at a certain time, and they vary each lunar month, and they almost certainly will not be right over your dial! The dial is then rotated daily around the polar axis. This is a PDF file of around 250k, and has a very simple discussion on three philosophical concepts of building lunar dials, and asks whether a purist would go for accuracy (using lunar and solar data), or would a purist use the moon and the moon alone. While formulae are provided to calculate new, full moon, and first and last quarter, this dial is simplicity itself. The general spreadsheet on this web site has lunar calculations added as a work sheet for both mean and true lunar quarter dates. The dial shown here is a rotating gnomon dial. NOTE: the formulae are approximations of approximations, they are close but not guaranteed. Second they refer to the mean lunar month, however the true lunar month can vary by plus or minus 6 hours from that mean. The spreadsheet has both mean as well as true lunar phase data. NOTE: I am not an expert in lunar dials. The PDF file has the templates, and photos show what they would look like. You are on your own however! ALSO ~ even during the month, the moon's rotation varies and can be off by 15 to 30 minutes compared to the first quarter (1q) calibration. general spreadsheet The North American Sundial Society has additional material for lunar dials on their optional CD. The spreadsheet has on the left side MEAN dates of lunar phases, the right side now has the TRUE dates. Actual lunar test on the pictured dial above show it to be within about 5 or 10 minutes once the monthly bias has been once set, preferably on the first quarter, but not required. It can be set on any day in the lunar cycle. And by setting it, longitude as well as the monthly bias are incorporated, thus this lunar dial is a standard time dial. No, it doesn;t have summer time incorporated. Puzzled about the ecliptic, and why the moon rises in the north east or southeast? Check the ecliptic dial section. Fabulous CAD pictorials. Simplified, and you should also download the ECLIPTIC dial info, it goes hand in hand with this it was also updated with this dial in mind. |