# The Naked Scientists Forum

### Author Topic: Could we use a Moondial for timekeeping  (Read 2161 times)

#### syhprum

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##### Could we use a Moondial for timekeeping
« on: 12/03/2012 10:17:57 »
Sundials make pretty poor timekeepers how much worse would a Moondial be

#### Soul Surfer

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• keep banging the rocks together
##### Re: Could we use a Moondial for timekeeping
« Reply #1 on: 13/03/2012 10:31:38 »
Sundials are very good timekeepers if you live your life by the light of the sun.  However we live our lives by constant clocks which do not take account of the fact that the earth's orbit is elliptical.

As an aside does anyone know when it was first observed that the precise time of noon (sun highest and due south) measured by a constant clock was not absolutely constant but varied each way by around a quarter of an hour.  The Greeks knew about the precession of the equinoxes and the approximate size of the spherical earth  Did they know this too?

A moon dial is a possibility and exactly the same as a sundial but using it to tell the time is more complicated because you need to know the number of days since the last new or full moon and do a calculation that will get you the time within about one hour.   Simple examples are, For a full moon midday (for a sundial) is midnight  for first quarter midday is 6pm.  It is 6am for last quarter.  The time shift is approximately one hour per day.

There are some other effects of the moon's orbit  like the rotation of the notes that will have an effect but it is probably small.
« Last Edit: 13/03/2012 10:39:59 by Soul Surfer »

#### syhprum

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##### Re: Could we use a Moondial for timekeeping
« Reply #2 on: 13/03/2012 16:14:47 »
I wondered if the correction for the elliptical orbit of the moon was more of a problem.
Of course the moons position relative to the stars was the best method of timekeeping before chronometers were developed for marine navigation but complex to use.
I did not realise when logarithms were drummed into me at school this was the main reason.
« Last Edit: 13/03/2012 16:18:30 by syhprum »

#### Don_1

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##### Re: Could we use a Moondial for timekeeping
« Reply #3 on: 14/03/2012 10:02:43 »
I had a moondial in the garden once. Trouble was I kept going ar*e over t*t trying to get to it in the dark and when I got to it, it was so dark, I couldn't see the bloody time anyway. So I started using a torch so I could see where I was going and see the dial. It was no good at all, it always seemed to show the same bleeding time!

#### The Naked Scientists Forum

##### Re: Could we use a Moondial for timekeeping
« Reply #3 on: 14/03/2012 10:02:43 »