# [time-nuts] How many seconds in a year?

Jim Palfreyman jim77742 at gmail.com
Wed Oct 15 05:19:20 UTC 2008

```Hi Neville,

There are a few inaccuracies in your summary but the figure you want for
J2000.0 is 365.242 190 419 SI days=31556925.252202 SI seconds. However we
cannot give you an average over the next 200 years because it is steadily
dropping by 5.324 ms per year. So in 200 years time it will be a second out.

However, for your purposes if you use the number above you will get very
close to what you want.

Regards,

Jim

2008/10/15 Neville Michie <namichie at gmail.com>

> I have been thinking about my problem, the major part of the problem
> is finding the right question.
> If leap seconds are applied to keep the meanderings of the planet in
> phase with our mean time
> clocks, then what about our leap year days which are applied to keep
> the seasons in phase with our
> calendars? Applying a whole day every so many years may keep the
> civil authorities happy,
> but when we all celebrate a new year we are not counting down the
> completion of a planetary cycle
> but the civil approximation to a new year.
> Now, having thought about it a bit more, the year is the completing
> of an orbit of our elliptical orbit around the sun.
> The start and finish of an orbit is defined by the inclined axis of
> rotation of the Earth crossing the plane of its orbit which is what
> causes the seasons.
> The elliptical orbit is moving, hence the precession of the
> equinoxes. As we can not measure a year
> by looking at a particular star crossing our meridian,
> we measure the year by watching a fictitious star crossing our
> meridian. This star (which used to be at the first point of Aries
> on the vernal equinox) is slowly orbiting around our solar system as
> our tilted ecliptic precesses.
>
> Which now gets me back to my question. If I want to make a clock that
> chimes once per solar year when we have completed a cycle it will
> count down a
> number of seconds then chime. So I want to know the number of seconds
> in a Mean Year, accurate enough so that in 200 years time
> it will still be right.
> It should be fun to see the time the new year really starts as we
> head around the orbit again. The time will not be midnight
> but will jump around in the day with different years.
> There are so many interference's in time keeping by accountants and
> politicians I was thinking of making a clock that
> showed real time as determined by sun and stars.
> Although that brings up the equation of time, and mean time is so
> convenient if you have an atomic clock.
> I might just try to make a clock that shows the mediaeval "Italian
> Hours", where every day has 24 hours with sunrise at 6 AM with sunset
> at 6PM.
> The old clocks had dials marked so that you read off the elastic
> Italian hours.
> cheers, Neville Michie
>
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