On May 1, 7:06=A0pm, Crown-Horned Snorkack <chornedsnork...@[EMAIL PROTECTED]
>
wrote:
> On 1 mai, 19:53, "Mike Dworetsky" <platinum...@[EMAIL PROTECTED]
>
> wrote:
>
>
>
> > "Crown-Horned Snorkack" <chornedsnork...@[EMAIL PROTECTED]
> wrote in message
>
>
>news:5b40436f-cb79-4966-807b-7b83b9eaacd8@[EMAIL PROTECTED]
>
> > >Well, when was it?
>
> > >The actual length of sideric day, and of tropical day, increases
> > >slowly, as tidal friction irreversibly slows down the rotation of
> > >Earth.
> > >The actual length of sideric year can change - the energy of
Earth=B4s
> > >orbit may change as energy is exchanged between orbital movement of
> > >Earth and other planets. But those changes are said to be minor. The
> > >changes in tropical year are likewise minor.
>
> > >The result is that the number of tropical days in a tropical year
> > >decreases.
>
> > >Sometime in palaeozoic, tidal rhytmites allegedly show that there
were
> > >400 days in a year.
>
> > >But the rate of tidal slowing is not constant. It changes with
changes
> > >in the configuration of shelf seas and ocean basins. There would be
> > >major changes during ice ages, for example.
>
> > >The true duration of tropical year is around 365,2423 to 365,2424
> > >tropical days. Gregorian calendar requires 365,2425 days.
>
> > >The ***ulative error of Gregorian calendar through recent is thus
less
> > >than two days.
>
> > >But how valid was Gregorian calendar in ice age?
>
> > The question is, in the everyday sense, meaningless, because the
Gregori=
an
> > calendar is not used for years prior to 1582. =A0Not for any sensible
pu=
rpose,
> > because the main event it was designed to regulate thenceforward--the
da=
te
> > of Easter--had already taken place in each of those previous years.
=A0(=
Later
> > in England--Newton was born on Christmas Day in the Julian calendar,
so =
we
> > still call that his birthday.) =A0Looking backwards for dates is what
yo=
u get
> > using a "proleptic" calendar and usually the Julian calendar is used
for=
> > this.
>
> This causes problems. Julian calendar is considerably farther from
> true length of tropical year than the Gregorian.
>
> > Aside from the removal of 10 days in 1582, the difference between
=A0Jul=
ian
> > and Gregorian is in the number of days in an average year: 365.25 or
> > 365.2425. So if you tried to decide the date in some very distant past
y=
ear
> > (e.g., 10,000 BC) you would have to account for that difference, or
abou=
t
> > .75 d per century or 7.5 days per millennium.
>
> And 75 days over 10 millennia. Which means that a proleptic Julian
> calendar is plainly out of alignment with seasons in early recent.
>
> In which calendar month did Laach lake eruption take place?
>
>
>
>
>
> > Of course we also have a ***ulative error in the sense that the actual
> > period length of a tropical year is 365.2422 days (to 4 decimals) so
the=
> > Gregorian calendar itself will gradually need some reforms; a leap
year =
will
> > have to be omitted, perhaps the year 4000. =A0I imagine the Catholic
Chu=
rch
> > will give thought to this in about 1700 years or so. (Could be an
> > interesting SciFi story theme?). =A0The error ac***ulated is about 1
day=
every
> > 3300 years rather than 4000 years, so in the very far future a further
> > reform might be needed.
>
> > The effect of changes in the rotation of the Earth would be smaller
but
> > would ac***ulate more rapidly as you went back in time. =A0The figure
fo=
r c.
> > 2000 years ago is of the order of three hours error. =A0See:
>
>
>http://www.blackwell-synergy.com/doi/pdf/10.1046/j.1468-4004.2003.442...
>
> > It is difficult to extrapolate rotational rates back accurately over
man=
y
> > millennia because more than tidal effects are involved.
>
> Indeed. However, they could be measured directly.
>
> Misalignment over a few weeks should show up in geologic record.
>
> > Astronomers use something called the Julian Day number which is a
runnin=
g
> > count. =A0The Julian period starts on 1 January 4713 BC (Julian
calendar=
) and
> > lasts for 7980 years. =A0It starts on the day when the Roman
Indiction, =
Golden
> > Number, and Solar number all had a value of 1. =A0This allows them to
av=
oid
> > having to use dates in one calendar or another for calculated events
in =
the
> > distant past (like eclipses). =A0For accurate timings they of course
hav=
e to
> > use a dynamical time scale independent of variations of Earth
rotation.
>
> Indeed. Julian day is bound to rotation of Earth which, in long term,
> is more variable than tropical year (bound to orbital movement of
> Earth). Neither of which is constant flow of time as bound to inertial
> laws.
>
> > When they define somenthing to be measured in years they usually use a
u=
nit
> > of Julian years of 365.25 days, e.g., if discussing the period of a
visu=
al
> > binary star, or the orbit of the Sun around the galaxy.
>
> Of course, it may be a question what the most im****tant year is:
> tropical, sideric or anomalistic...- Hide quoted text -
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -
You guys will never get it !,,the 24 hour day is required first
before you can create a 1461 day calendar system of 3 years of 365
days and 1 year of 366 days or rather a leap day every 4th
year.Without the human devised equable 24 hour day then it is
impossible to create a calendar system with the fractions of hours
minutes and seconds needed to create a leap day every 4th year.As leap
days were already in operation in antiquity,it follows that the
equable 24 hour day is even older -
http://apod.nasa.gov/apod/ap040229.html
I know how the equable 24 hour day is created in modern times* ,how it
was done in antiquity is anyone's guess -
"Draw a Meridian line upon a floor (the manner of doing which is
sufficiently known; and note, that the utmost exactness herein is not
necessary:) and then hang two plummets, each by a small thred or wire,
directly over the said Meridian, at the distance of some 2. feet or
more one from the other, as the smalness of the thred will admit. When
the middle of the Sun (the Eye being placed so, as to bring both the
threds into one line) appears to be in the same line exactly you are
then immediately to set the Watch, not precisely to the hour of 12.
but by so much less, as is the Aequation of the day by the Table."
Huygens
http://www.xs4all.nl/~adcs/Huygens/06/kort-E.html
No doubt Androcles will suggest a stopwatch and two sticks to affirm
axial rotation using the return of a star but the excerpt above shows
the actual creation of the 24 hour day itself,the core of all
timekeeping in other words and the basis of accurate clocks,equable
hours,minutes and seconds and the correlation between the daily cycle
and terrestrial geometry/geography.
There is nothing like that raw astronomical experience where the human
devised 24 hour principle is appreciated using both reasoning and
observations and the realm of men who appreciate that it stretches
back to antiquity.As for those mesmerised by axial rotation tied to
the solar/sidereal fiction,the noble astronomical experience will
always be denied and rightly so as the contem****ary mutation amounts
to a childish view.
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