Ticker for September 18, 2002

                
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September 18, 2002 September 18, 2002 September 18, 2002 September 18, 2002


Last Chance to Cast a Southward Shadow for a Long Time

As anybody who drives on east-west streets around sunrise or sunset
can tell you, the autumnal equinox is approaching.  That's the day
that the sun rises and sets exactly in the east and the west (this
is the part where a really picky Ticker author would point out that
the equinox is not a day, but an exact time, and blah blah blah).

This year's equinox occurs on September 22nd, at 11:55 pm CDT.  That's
almost six hours later than last year's autumnal equinox.  Why's that?
Because our trip around the sun lasts 365 days, plus a pesky 5.81
hours.  We correct for those 5.81 hours by adding a 29th day to
February every four years.

But wait, there's more!

Actually, because 5.81 is clearly not 6.00, our leap years actually
over-correct for that time.  How do we correct the over-correction?
By decreeing that the "00" year is *not* a leap year (i.e., 1900
did not feature a Feb 29th).

Does your head hurt yet?  We're just getting started!

But that correction of the over-correction is an over-correction of
its own right.  So, how do we correct for that over-correction?  By
decreeing that every fourth "00" year really *is* a leap year, despite
what the last rule might tell you.  That explains why 2000 did, in fact,
carry a 29th day of February.

Alas, this, in itself, is not a perfect correction.  Therefore, the
autumnal equinox will continue to migrate through the calendar despite
all of these carefully laid out rules.  So, how do we fix that?
WE CHEAT!!!  We just carve a few seconds out of the calendar once
every few years to keep us on track.

Anyway, the first few minutes before/after the sunset/sunrise of the
next few days offer your last chance to cast a shadow that has any
southward tilt to it, as the sun will rise and set to our south for
the next six months.  Enjoy it!