[time-nuts] Re: Primary frequency standard

[Poul-Henning Kamp]

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Lux, Jim writes:

> Would a sundial  (or zenith meridian crossing sensor) be a primary 
> standard for measurement of a solar day?

Using Corbys "desert island" criteria, I think the answer is "yes(footnote)".

Imagine you wake up, teleported to a different planet, about which you know nothing.

First you need to establish the orientation of the planets rotational axis, because your sundials'gnomon' must be aligned parallel to it.

You can do this by measuring the minimal and maximal noon elevation of the appearant sun over approx 60% of the planets "year".  As a side effect you get a pretty good idea how long a "year" is in "days".

Note that unlike this planet, there is no guarantee that these two numbers "mesh" well, or even which is the longer time interval[1].

Next you need to partition the scale in however many "hours" you want, but that is simply an invariant exercise of constructive geometry.

So I think the answer is yes.

However, the footnote is that your sundial is only primary on that particular latitude, and it is debatable if it is even that, if the planets rotation has any chaotic or higher order components, such as nutation and all that stuff.

[1] See for instance Venus:  A venus-day = 243 earth-days, but a venus-year = 225 earth-days.

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