Vernal equinox dates for 5000 BC, etc.

[Sankaranarayanan K V]

Dear Dr. Rao,

I don't have ready dates. But perhaps the following resources might help you if you haven't tried them already:

For up to 5400 BC into the past you can try the Swiss ephemeris:

http://www.astro.com/swisseph/ 

ftp://ftp.astro.com/pub/swisseph/programs  - download the swewin32.zip and run the swewin32.exe file to ephemerides up to 5400 BC in the past.

For dates further into the past, you can try using the programmatic interface of the same Swiss ephemeris.  

But accuracy would reduce further because we can't estimate Delta T well into the past - http://en.wikipedia.org/wiki/%CE%94T .

You can also try the ephemeris programs from http://www.moshier.net/ .

A fourth option is this:

Download the zip from the link - http://www.thep.lu.se/~larsg/astromodels.zip - and use the Almagest.xls or other spread sheets.

There is some accompanying documentation which talks of the models used.

Regards

Sankar

On Sat, May 5, 2012 at 2:53 PM, Balachandra Rao <balacha...@gmail.com> wrote:

Dear Friends,
       Currently I am working on the correctness of our classical
Indian astronomical texts for atleast a few thousands of years B.C.E.
Can some of you tell me the dates (by Julian cal.) of vernal equinox,
say for the years -5000 , -10000 and -15000 ?
Regards,
Balachandra Rao

[Sankaranarayanan K V]

I have an Android app called PlanetDroid ( http://www.strickling.net/android_engl.htm#PlanetDroid ) which seems to give results for any date. So here's what you wanted:

Vernal equinox dates:

-15,000 years - July 5th

-10,000 years - June 5th

- 5,000 years - April 30th

      0 years - March 22nd

The app uses AstroLib (http://mhuss.com/AstroLib/docs/api/index.html) and that uses VSOP87 theory to compute ephemeris.

Regards

Sankar

[Sunil G.R.]

Whatever may be the software. Does it take the short month of September or October in 16th century? I forgot the particulars of month, days-in-it and year. Will post it if i could recall!

I think it has 2 weeks less in that month. Initially Makara-Sankranti and Tamil-new-year was falling on Jan1 and Apr1. And due to this change in short month, they started falling on Jan14 and Ap14. (I am not talking about the Ayanas here).

Thanks,
Sunil.

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[Balachandra Rao]

Dear Sankaranarayanan,
Thank you very much for the interest & trouble you have taken
in computing the vernal equinoctial dates for remote centuries BCE. Of
course as you pointed out the possible inaccuracy in estimating
delta T is a factor responsible for the difficulty. Further, in the
basic formulae for the mean long of the sun higher powers of julian
centuries may cause errors.
Any way, by my computations I get the dates for sun at
vern.equi. close to the dates you have given. In fact when I got dates
in June & July my first reaction was one of shock! But now that you
have given me similar dates I feel truly relieved. I compare our
results in what follows:
Year Vernal Equinoctial Date
KVS SBR
0 Mar 22 Mar 24
- 5,000 Apr 30 May 03
- 10,000 Jun 05 Jun 08
- 15,000 Jul 05 Jun 24
(Note: The dates as per my computations are according to the Julian
reckoning and not Gregorian).
With regards,
Balachandra Rao

On M on, My 7, 2012 at 6:34 PM, Sankaranarayanan K V <kvsa...@gmail.com> wrote:

[Anand Sivaram]

US/British system changed to Gregorian in September 1752, before that it was
Julian only.

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[Sankaranarayanan K V]

Sunil,

It depends on the software. At least PlanetDroid works correctly. Thursday, 4th October, 1582 is followed by Friday, 15th October, 1582. Software applications with flexible calendar support will let you indicate what calendar you are using when you enter a date.

Regards

Sankar