[LEAPSECS] Straw men

[Gerard Ashton]

On 1/9/2012 2:40 PM, Ian Batten wrote:

> So long as those all tick the same thing, its relationship to the rotation of the earth is, +/- several hours, irrelevant.  No-one cares what the relationship between their watch/clock/computer and the sun is at anything other than the grossest scale


The foregoing statement is just not true. The time of sunset and sunrise 
is important
in many applications other than astronomy. It is important in all 
outdoor activities
where artificial light sources will not be carried. It's important for 
pointing some
solar arrays, and modeling the output from the same.

Of course, changing the disseminated global time scale from UTC as presently
defined will not cause an immediate problem for these applications.  A 
common
rule of thumb is that a measurement standard should have a tolerance no
more than 1/3 of the device under test. If the device under test is a 
wrist watch,
and it is required to have a tolerance of 1 minute, then the measurement 
standard
should have a tolerance no worse than 20 seconds. This would suggest 
sunset/sunrise
tables that are to be enforced with a wrist watch should have calculations
that are accurate to no worse than 20 seconds. Treating the difference 
between
UTC or its successor and mean solar time as negligible becomes inadequate
for use with wrist watches in about 30 years.

Gerry Ashton