Thursday, 14. October 2010

Since last week we discussed timekeeping throughout the daytime by use of the sun, it would only figure that this time we move towards the evening.  The ring dials appropriate counterpart is known as the Nocturnal and works on quite a bit of a different principal.  Since there is no sun to work off of to measure rotation and the moon is highly variable, we have to use the stars. The only downside to this if you’re not entirely familiar with your constellations, you’ll need to figure them out (or at least 3 of them.) to properly use the device.

The Nocturnal

In this case our reference point is Polaris; the north star.  Since the other constellations rotate around this on a yearly basis for us, by using their position in the night sky we can accurately determine the time.  Polaris is sighted through the center hole and the other reference constellations.. Cassiopeia, Ursa Minor and Ursa Major are clocked around the outside of the nocturnal.  The time is indicated in the local mean time and needs to be corrected for local time.

Some of the smaller models tend to be accurate within 15 minutes, but apparently the full sized models (Which used about an 8 inch disk.) could tell time within 2-3 minutes. With accuracy like this, it is no wonder that mechanical timepieces took such a long time to catch on.  In addition, based on the position in the sky, the ships latitude can be determined as well, which is typically based on a scale off of the back of the instrument.

Of course, I would be remiss without including a similar Project to demonstrate how the device works.  Like the other timepiece this one is best made out of card stock.   This is also “slightly” more complicated, requiring a rivet with a hole in it to sight the north star. It’s also worth noting that many cities probably have too much ambient light to really make this work, so you’ll need to head out into the country or someplace thats darker to easily see the stars you need. Happy hunting!

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One Response to “Nocturnal”

  1. Don Says:

    My D&D 4E game has a non-standard pantheon that is not alignment based (gods are really far too complex to adhere to mortals’ good/evil ideas).

    In it, the priests of the nature goddess are typically responsible for timekeeping. Priests to this deity learn to make candles to mark the passage of hours, and light the candle at daybreak each day. Each candle lasts 6 hours and the priests ring the temple bell every hour (or only a few times a day depending on the size town).

    Of course, the priests also sell the candles to those who need accurate timekeeping, and this makes up much of the church’s income.

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