Somebody wrote:

> <<The problem deals with time.  One would need to measure the time back
>  to the Big Bang and use that as day one.  Or two, or 42.  It's all
>  relative.  I recommend the book A Breif History of Time by Steven
>  Hawking.  Matter of fact maybe we can get a team together and set up a
>  teleconference with Dr. Hawking.>>

Followed by Steve Dirickson:

>  Why would we need to track back to some putative "Day One"? Calendars are
>  a purely human invention-the universe doesn't care. Since calendars are
>  something we create for our own convenience, they can be, and should be,
>  organized for optimum utility.

As a practical matter -- although, as it has been alleged, practical matters
don't much matter in this form of discussion -- calendar "days" are defined
geo-(Earth)-centrically. One dawn. One sunset. Next dawn. One day. One tick
of the calendar.

Thus it would be somewhat difficult to have a calendar that pre-dates the
formation of the Earth. Nor is even extrapolation possible. It's generally
agreed that the rotation period of the Earth (the length of one day), at the
time of the Earth's formation, was about 9-10 hours in length. Moreover, the
Moon, when it solidified, was only about 20-30,000 miles above the surface of
the Earth (in comparison to its average 231,000 mile orbital radius now).

The Moon would have consumed a good portion of the sky when it was overhead 4
billion years ago. But more than that, mountains on both the Earth and the
Moon would have audibly creaked and groaned under the tidal stresses
attendant to the "monthly" passage of the Moon around the Earth. Skyscrapers
are designed, even today, to gently sway back and forth with the passing of
the Moon. Four billion years ago, the tidal force was 50 times as strong --
strong enough to create sufficient heating to melt surface rock on both
planets [indeed, the mare (the dark areas) that you see on the Moon were
formed about 3.5 billion years ago and have remained essentially unmodified
since, other than for minor contractions due to core cooling and
late-formation impacts).

Heat loss associated with the global Earth-Moon system due to tidal friction
is the reason the Earth's rotation is slowing down -- and the reason that the
Moon is slip-sliding away and will eventually become its own planet (just as
Neptune lost Pluto). That heat loss is also the reason we must every so often
add a leap second to the calendar. Each new second that is added represents
another step in the Moon's departure.

If we really did want to have a calendar that went back to the beginning of
time (for at least this cycle in the Big Bang) and day length were to be
extrapolated backwards, even before the existence of the Earth-Moon system,
we would have an intersection with the x-axis (zero day length) at about six
billion years ago. All days prior to that would be of negative length, making
the process of making and keeping appointments somewhat confusing.

Wirt Atmar