Clocktime: Tompion & Banger Sidereal Regulator 1708, 02 Sidereal

Thomas Tompion & Edward Banger - Sidereal Tompion Regulator No. 483 fixed sidereal hour ring, rotating GMT ring from extended hour hand.
Join Dr John C Taylor OBE from the Clocktime digital museum as he discusses sidereal time of the Tompion & Banger Sidereal Regulator, circa 1708.
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Generally, everything you learn about time at school is wrong. How long does it take the Earth to make one revolution? Now most people say, well, 24 hours. Would it surprise you to know that the Earth makes one revolution in 23 hours 56 minutes 4.09 seconds? But this is one revolution looking at the Earth from space, whereas on the Earth we don't measure time from space, we measure time by the Sun and so the time from noon to noon on the average is 24 hours. But never in the history of universe has there been any day where the solar revolution has taken place in 24 hours. Difficult to believe but there has never been a day which is exactly 24 hours long. What happens is that the Earth's orbit is elliptical and the elliptical orbit means that once we've done one revolution, we then have to turn a little bit more to face back into the Sun again as the Earth goes around its orbit. And because the orbit is elliptical, every day it's slightly different. It goes up to 15 minutes out and 15 minutes the other way. That's called the equation of time but sidereal time is constant. It's because the stars are so far away, if you take the time from the rotation of the earth round and back again then that's sidereal time. It's because this is entirely used by astronomers to place objects in the heavens and to know where to look with their telescopes to see a particular object. And so you can calculate where it is using sidereal time and of course time going round in 360° is 24 hours and so that you can have either in degrees or hours, minutes and seconds, whichever is the more convenient. This one gives you hours, minutes and seconds of sidereal time.