Takashi SUGA wrote:
....
> Postscript
>
> Simon Cassidy wrote:
> | a) falsehoods in astronomy
> |texts (which claim that "the mean interval between vernal equinoxes"
is
> |the same as the period of the tropical longitude of (an unreal object
called)
> |the mean sun
> Please observe vernal euinox date/time every year, we will find that
the interval
> between succsessive vernal equinox is varied each year. Because perturbation
> and nutation are exist. Vernal equinox year length is abstructed
"unreal
> object" too. [Takashi SUGA's response to the unreality of the mean
sun]
Simon notes:
It (the mean interval between vernal equinoxes) is abstract
in the sense that no single interval between sucessive vernal
equinoxes can be used, in isolation, to quantize it. But its
degree of abstraction is the minimum required for use in a
rule-based schematic calendar (of the first order, as are all
rule-based calendars adopted to this date). Any interval
represented as characterizing the period of any physically
measurable repetition cycle, has, at least, this minimal level
of abstraction. The abstraction necessary for understanding the
concept of "the modern astronomers mean tropical year" is so
extreme that even contemporary professional astronomers get
confused and state falsehoods when trying to explain it. For
a good example of this I include below emails betwen myself and
the astronomer Dirk Husfeld:
******************************************************************************
Subject:
http://www.maa.mhn.de/Scholar/times.html
Date:
Mon, 02 Feb 1998 11:49:28
-0800
From:
Simon Cassidy <scassidy@earthlink.net>
To:
husfeld@
Dear Dirk,
in your web-page you state:
"To obtain a more even time scale, one defines a fictitious
``Mean Sun''.
This Mean Sun takes the same time from one vernal equinox
to the next
as the true Sun, but it is supposed to move with constant
velocity along
the celestial equator. "
I believe this is incorrect. According to Jean Meeus in your reference,
(Astronomical Algorithms, Willmann-Bell, Richmond/Virginia, 1991, Ch.27
p171)
the Mean Sun of the celestial equator coincides at the equinoxes with
the
fictitious mean sun of the ecliptic and not with the true sun (which
coincides
with the fictitious mean sun of the ecliptic at the perihelion and
aphelion).
This may seem a minor detail but endless confusion is caused by such
mistakes.
For example you go on to discuss different types of solar years relevant
to
calendars (and particularily our Gregorian calendar) and fail to mention
the
type of year most relevant to the Gregorian and Persian calendars.
This is the
vernal-equinox year which (due to mistakes such as the above) is consistently
and wrongly confounded with the astronomer's mean tropical year. This
leads
to wrong conclusions concerning the accuracy of the Gregorian calendar
and the
future placement of leap years in the Persian calendar.
The "mean interval between vernal equinoxes" is not 365.2422 days, despite
the
Greenwich Royal Observatory and the Supplement to the Astronomical
Ephemeris,
but is 365.2424 days (to the nearest ten-thousandth of a day) as given
by
Jean Meeus and Denis Savoie in "The history of the tropical year, "Journal
of
the British Astronomical Association v102#1,1992,pp40-42. Also see
Albert Van
Helden's http://es.rice.edu/ES/humsoc/Galileo/Things/gregorian_calendar.html.
One thing I have discovered that Meeus does not cover is the remarkable
stability
of the vernal equinox year which should retain its value to within
about one
ten thousandth of a day from about 4000 BC to 4000 AD after taking
into account
the changing rotation of the earth. This makes it even more significant
calendrically and therefore it is lamentable that so few know of it
and that so
many false statements are made about it. See my web pages on this topic
at
http://www.magnet.ch/serendipity/hermetic/cal_stud/cassidy/err_trop.htm
*********************************************************************************
Subject:
Re: http://www.maa.mhn.de/Scholar/times.html
Date:
Sun, 10 May 1998 12:28:19
+0100 (MET DST)
From:
Dirk Husfeld <husfeld@>
To:
scassidy@earthlink.net
(Simon Cassidy)
CC:
Chris.Kronberg@
Dear Simon,
first of all let me apologize for coming so late with my reply
to your comment on my calendar/time-keeping web-page. I am not
working anymore at the Munich observatory so I can check my
mailbox there only now and then, and find even less time to
spend on demanding questions like yours.
I really do appreciate your comments. I could immediately see
the first point you made (about needing two mean suns) but it
took me a bit to understand the second point about the true
definition and length of the tropical year. I think I now
understand this and I do agree. However, I am not sure whether
this material (that as you wrote yourself is often overlooked
by professionals) should go into a web-page that intends to
explain basic terms to laymen. I find this insight fascinating
and would love to explain these matters to those interested.
But on the other hand, I also fear that by going into such
involved matters I would intimidate the main audience of the
web-page. I haven't made up my mind yet of how to handle this,
perhaps I will be using some kind of footnote approach. In any
case, I would like to say thank you again for pointing this out
to me, you certainly improved my knowledge.
With best regards,
Dirk Husfeld
*********************************************************************
end of email copies.
---
Dee's Y'rs, Simon Cassidy, 1053 47th. St. Emeryville Ca. 94608.
ph.510-547-0684.
email: scassidy@earthlink.net
