[LEAPSECS] Solar time: From mean solar days, to mean solar years

[Preben Nørager]

In the discussion about whether or not to drop the leap second, I think it
is not a question about solar time or not solar time. It is in other words
not a question about either solar time or atomic time.



If we drop the leap second it will be in favour of another timescale, which
uses only atomic clocks to tell the time, but the time in that other
timescale will still be based upon a kind of solar time.



About a hundred years ago it was decided, that the mean solar year, and not
the mean solar day, should be the unit of international time.



In 1960 the second was defined as 1/31556925,9747 of the mean solar year,
and in 1967 the second was redefined [equally in length to the previously
defined second] as the duration of 9192632770 periods of radiation.



When the second was defined in 1960 it was defined as a fraction of the
so-called tropical year. That was a mistake of wording. The tropical year
is a measurement of the solar longitude on the ecliptic, but the
international definition of the second is not based upon measurement of the
solar longitude on the ecliptic.



The definition of the second is based upon Newcomb's theory of the solar
system, and in that theory it is the barycenter of the solar system, and
not the center of the sun, which defines the length of the solar year.



The length of the solar year, according to Newcomb’s theory, is the time
for the longitude of the barycenter of the solar system to increase 360
decrees.



The solar year, thus defined, can be measured either for one year, or for
an average of years.


But the 1960 and the 1967 definition of the second can also be used as an
international definition of the mean solar year.


I think we should drop the leap second, and continue UTC without leap
seconds as TI [International Time], so that 1 mean solar year is the
duration of 290091231835491000 [31556925,9747x9192632770] periods of
radiation in the caesium atom.
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