Byzantine Sundial-Calendar - Part 1 (Patreon)

Byzantine Sundial-Calendar - Part 1

Byzantine Sundial Calendar, Part 1, by Clickspring. In this video, I lay out the design for a modernized version of the device known as the Byzantine Sundial Calendar. _______________________________________________________ A very special thank you to Patrons Mitchell Collins, Daniel Cohen, Larry Pardi, Sean Kuyper, Samuel Irons and Dan Keen ________________________________________________________ * From NASA's Solar Eclipse website: "If New Moon takes place within about 17° of a node, then a solar eclipse will be visible from some location on Earth." The actual value ranges from 15.39° to 18.59° because of the eccentricity of the Moon's (and Earth's) orbit. More info at: https://eclipse.gsfc.nasa.gov/SEsaros/SEperiodicity.html Abbreviated Transcript: 00:06 Before I make a start on constructing this clever little device, I'd like to give you a bit more of an overview of what it's all about. In addition to being the 2nd oldest geared mechanism on record, it also has the honor of being the world's first combination instrument. And by that I mean its both a portable sundial, and a calendrical calculator all in one. 00:48 Which suggests that this was a reasonably common piece of every day carry for your wealthy Greek or Roman citizen, although I think its fair to say this would probably have been the deluxe version! 00:59 Now there's an unavoidable approximation that must be accepted in its design, and it takes a bit of thinking to convert from temporal hours. But providing the user keeps the sun in the plane of the gnomon assembly, it gives a remarkably good reading of the time. 01:12 I should also point out that although I've specified separate northern and southern hemisphere indicating dials, there's no technical reason why the dial can't be laid out as a universal dial usable in both hemispheres. The latitude indicator could easily run through to 90 degrees on the other side, and the geometry still works. Just flip the gnomon over to clear the input ratchet when you change hemispheres, and you're good to go. 01:53 OK, now as cool as that sundial is, the geared portion of the mechanism is where I think most of the fun will be for this project. The original artefact was purchased by the Science Museum in London in the early 80's, and if you ignore the modern aspects of this version of the device, essentially the bits that they purchased were these. Most of the device was missing. 02:13 It took the brilliant research of then Curator of Mechanical Engineering, Michael Wright, to understand what it was that they'd purchased. In fact he built a beautiful reconstruction thats now on display in the museum, that faithfully replicates both its function and aesthetics. But its important to note: there's no eclipse prediction gearing in the original device, only calendrical information was displayed. 03:23 I'm treating it as a sort of investigative process as much as a build project. The engineering detail on the sundial calendar is quite similar in a lot of respects to the Antikythera mechanism. So much so in fact, that I think it'd be a bit redundant to take the same hard line approach with its construction. 03:53 I've used cycloidal teeth rather than the original triangular teeth, and a more modern horological layout for the supporting structure. English replaces Ancient Greek on the displays, and modern city names will be included in the latitude table. Preferably without any typos! 04:09 I've had a crack at correcting the Equinox error of the original dial, and I've also added a small ratchet disengage cam, to permit rapid scrolling forwards and backwards in time, when predicting eclipses. Beyond that though, the basic concepts, and engineering sensibilities are pure Byzantine Sundial Calendar. 04:28 Little or no clearance between the wheels, truly archaic pivoting, and the ancient concept of pinning assemblies to hold them in place. 04:45 It calls the type of eclipse correct every time, and the date is correct within a single day, for at least 4 years out from the setting date, after which the gear train starts to drift and needs to be reset. Despite its limitations, It's an absolutely outstanding teaching tool, for understanding key astronomical concepts. 05:02 Like the motion of the sun and moon in the ecliptic, the way latitude affects the way we see the sun, and most of all, what causes eclipses. OK, so enough of the prep, In the next episode I start making chips. If it all goes well, I just might get it all done in time for the big one of 2017. References: Gears from the Byzantines: A portable sundial with calendrical gearing J.V. Field & M.T. Wright Greek and Roman Portable Sundials - An Ancient Essay in Approximation M. T. Wright The London Sundial-Calendar and the Early History of Geared Mechanisms M. T. Wright Byzantine Sundial Calendar, Part 1, by Clickspring.