[LEAPSECS] Equation of time

[Richard Clark]

These simple expressions given each year in the Almanac or in the Astronomy
with Your Calculator books of the 80s are typically accurate to the few
seconds level. There was a short-lived annual publication called The
Almanac for Computers (late 70s and 80s) that showed some interesting
variations on these expressions.

It would be possible to carry out the angle expansions to higher orders
but rarely done. (I fiddled around with this once and found that
convergence beyond 3rd order in e and y was slow) This accuracy is
already beyond the realm of sundials and getting into 'observatory
grade' equipment and measurements. A more complete theory of the sun--
Newcomb, VSOPxx, JPL's DExxx, etc would be used.

Richard Clark
NSO/NISP
Tucson, Az.

On Thu, 5 Feb 2015, Tom Van Baak wrote:

> Someone asked me about accurate calculations of the equation of time. Since it relates to keeping time, leap seconds, and days perhaps someone on the list can shed light on it.
>
> Most graphs of EoT appear accurate to the minute. Is it possible to predict the equation of time to the millisecond level? How complicated are the equations. What sorts of non-obvious corrections does one need to apply at the seconds level or milliseconds level?
>
> Are the simple formulae given in http://en.wikipedia.org/wiki/Equation_of_time valid at this level, or is there serious literature that goes into far more detail.
>
> Thanks,
> /tvb