"R.H. van Gent" wrote: > > Ania Marczyk wrote: > > > I was wondering if anyone could shed some light on how to calibrate a > > nocturnal for a given latitude. I understand the principal of > > nocturnals, but have absolutely no idea of the angles involved either > > for Polaris to Ursa Major or how latitude affects these. Any info > > would be gratefully received. Thanks > > There is no latitude calibration - that is the beauty of these things. > > The calendar scales do need adjustment for the star (Kochab or the > Pointers of Ursa Major) you set the hour handle to and the epoch > (stellar precession). > > For instance, for Kochab lower culmination at mean local midnight (the > hour handle then points downwards to the 'six o'clock' position) should > occur on 4 November. For the Pointers, the mean local midnight lower > culmination occurs on 7 September. > > -
A longitude adjustment, to convert from local apparent time to zone time, is possible. I have made a nocturnal on which the first step is to set the longitude by aligning the index arm with your location on a map engraved on the main handle. The second step is to set the date by turning only the date disk to align it with the index arm. My map shows only the British Isles, but the same principle could be used anywhere. I have not seen any other nocturnals that show zone time in this way. Perhaps because the notion of time zones is rather recent. Chris Lusby Taylor 51.3N, 1.4W -
