Dear Brent,
Thank you for your follow-up...
While I am trying to digest all of that I
have a new question.
Do the ancient solar calendars like the
Incas still work?
Do their rocks still show where the
solstices will occur now?
I am not an expert in this area and others
may supply more detailed comments. I can
see no reason why such instruments cannot,
at least approximately, show when the
solstices occur but there are practical
difficulties...
Around the solstices, the declination changes
ever so slowly, so pin-pointing the precise
moment of a solstice is hard even with modern
instrumentation.
Also, the obliquity of the ecliptic keeps
changing and this affects the declination
at the solstices and hence the direction
of the sun at sunrise and sunset at those
times.
Your explanation below seems to indicate
that their calendars would get progressively
worse in predicting the day of solstices.
Well, their instruments (if you can call them
that) will give progressively worse indications
of the day on which the solstices fall but that
isn't, quite, the same thing as commenting on
the associated calendar. The Gregorian calendar
suffers from drift but that has nothing to do
with the change in the position of sunrise at
the solstices!
On a side thought, the problem seems to be
that we are using the time for the earth to
spin around (a day) to measure the time it
takes the earth to go around the sun (a year).
These are two different events and it doesn't
make sense to use one to measure the other.
Well, it makes some kind of sense. We need to
know how many days there are in a year for all
kinds of reasons. The snag is that the ratio
year:day is not a constant.
A day is a day and a year is a year, we
shouldn't mix the two as it makes for a
very messy situation.
Alas, the closer you look into the behaviour of
the Earth-Sun system the messier it gets. The
variability of the year:day ratio is just one of
many messes.
Forget the Popes calendar...
I do my best :-)
...can't I make a solar calendar that depicts
a true solar year?
Well, only up to a point.
It would mark the two solstices, the time between
those two points is half a solar year.
That is your first mistake. The time between the
winter solstice and the summer solstice is not the
same as the time between the summer solstice and
the winter solstice. You instantly fall into the
problem of having two different lengths of half-year.
Half way in between those are the two equinoxes
which would mark 1/4 of a year and we could keep
halving the differences to get 1/8, 1/16, 1/32,
1/64 of a year etc...
Alas, your four quarters are all of different length
and your eight eighths are all of different length
and so on. This may not matter but you would have
to accept that your sub-divisions are not the same
length.
So we don't try to define a year in earth days
but just split up a true year into equal parts.
Yes. I can buy that scheme but your parts are
not equal alas! Just try counting the days from
the March equinox this year to the September
equinox and then count the number of days from
the September equinox to the March equinox next
year. You will find over a week's difference.
To be sure, you are not wanting to use the day
as a unit of time but you are wanting to use
the half-year as a sub-unit and your half-years
have different lengths.
And this solar calendar would need no leap
year and would always be correct.
There is something in what you say but I am
not sure that the word calendar is appropriate.
To me, a calendar really is about relating days
to years. Pope Gregory's scheme is one way to
do this. Your proposal, which does its best to
ignore the concept of a day, is something
altogether different.
Maybe :)
Maybe indeed!
All the best
Frank
