[time-nuts] Re: Derivation of time from celestial sight

[Hal Murray]

brent.evers at gmail.com said:
>  My understanding (and I could be wrong) is that one could derive 'stellar'
> time from a start sight/fix on polaris or another well tracked celestial
> object.

I think Polaris is a bad example, actually worst case.  You want something 
close to the equator so its position changes as the Earth rotates.

This is the same idea as using GPS for timing.  If you know where you are 
located, you can reverse the calculations to get the time.


> Any idea what type of accuracy can be expected?

How good is your telescope?  and the mount?

The unit is arc-seconds.

The moon is 1/2 degree in dia.  So if you want 1 second of accuracy, you need 
to measure the position of your chosen star to 1/7200 the diameter of the moon.

The USNO used to be the national source of time.  Google found:
> Visual Transit Circle telescopes are being replaced by newer instruments
> capable of determining stellar positions to an accuracy of 0.01 arcseconds.
> USNO ...
(but their web server didn't give me that page)

Somewhere down at that level of detail you run into problems with the 
instability of the atmosphere.


I think there was a thread several years ago on tracking the sun with 
something as simple as a camera connected to a computer.


-- 
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