MadSci Network: Other
Query:

Re: how can you tell time without a watch or clock

Date: Thu Mar 23 10:26:52 2000
Posted By: Andrew Karam, Staff, Radiation Safety / Geological Sciences, University of Rochester
Area of science: Other
ID: 953695387.Ot
Message:

There are three scientific ways to do this, both of which involve some 
astronomy.  The easiest is to simply wait until the sun is due south (in 
the northern hemisphere), at which time it's high noon at your location.  
With a sundial, you can extend your solar time-telling, but it's hard to do 
by eye.

At night, you can tell time using the "handle" of the Big Dipper as the 
hour hand on a clock - the direction it's pointing indicates the 
approximate time.  This is not nearly as accurate as using the sun, though.

Finally, if you have a telescope, you can look at Jupiter's largest moons. 
 Each has a different orbit and, by noting their relative positions as one 
or more passes in front of or behind Jupiter, you can tell the time very 
precisely.  Unfortunately, to do this, you need a telescope or good 
binoculars, a book with the orbital parameters of the moons, and a 
calculator.  However, this method is so precise that it was used by Lewis 
and Clark and many others to determine the exact time and, from that, their 
longitude (i.e. distance east or west of the Prime Meridian in Greenwich, 
England).  

The best sources of information about telling time are Daniel Boorstein's 
book, The Discovers and another book called Longitude, by Dava Sobel.

If you don't have access to the sun, the Big Dipper, or a telescope, your 
best bet is to ask a kind stranger who seems to be wearing a watch.


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