RE: equinox solar declination

Sat, 22 Sep 2001 11:37:09 -0400 (EDT)

Dear John,
 
I calculated what you need (according to Meeus' truncated VSOP87 theory):
 
Time (Tucson, AZ) Declination (Degrees:Minutes:Seconds)
 2001/09/22 08:50:00.0000 [+6 gives UT]
 
  0:07:56.6049
 2001/09/22 08:55:00.0000 [+6 gives UT]
 
  0:08:01.4713
 2001/09/22 09:00:00.0000 [+6 gives UT]
 
  0:07:51.7385
 2001/09/22 09:05:00.0000 [+6 gives UT]
 
  0:07:46.8721
 2001/09/22 09:10:00.0000 [+6 gives UT]
 
  0:07:42.0057
September Equinox
 2001/09/22 17:04:30.6638 [+6 gives UT]
 
  0:00:00.1298
September Declination Zero
 2001/09/22 17:04:38.5840 [+6 gives UT]
 
  0:00:00.0000
 
I used The Sun API (www.sunlitdesign.com/products/thesunapi) and Excel.
 
By way of example: the time of the September Equinox may be found using the Find Annual Feature function    The Find Annual Feature function takes two parameters.  The first is any date in the year that is to be searched and the second is the feature that we are searching for.  The Find Annual Feature function returns a Modified Julian Day.
 
sdxFindAnnFeatx(sdMJDx(2001,1,1,0,0,0,6),sdFeatEquinoxSep())
        =  "52174.9614660165<MJD> 52174.9614660165</MJD><TimeZone>6</TimeZone>"
 
Repeating the example and using the Time To Text function gives us the calendar day for Tucson, AZ
 
sdxTime2Text(sdxfindannfeatx(sdmjdx(2001,1,1,0,0,0,6),sdfeatequinoxsep()))
    = " 2001/09/22 17:04:30.6638 [+6 gives UT]"
 
These numbers above agree nicely with: 

  http://aa.usno.navy.mil/data/docs/EarthSeasons.html

 
Regards
 
David Pratten
Author - The Sun API
 
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]On Behalf Of John Carmichael
Sent: Saturday, 22 September 2001 8:53 AM
To: [email protected]
Subject: equinox solar declination

Hi all:
 
I'm getting this message out a little late, but tomorrow on the equinox,  I'd like to check the solar declination of the nodus's shadow. (Of the Flandrau heliochronometer). I want to see if the center of the shadow is centered exactly on the 0 degree line at the exact moment of equinox.
 
My astronomical calendar says that the equinox occurs here (in Tucson AZ) at exactly 4:05 pm.  But since the declination is changing so quickly this time of year, I'm wondering if the shadow will be exactly on the 0 dec. line in the morning too.
 
Does anybody know what the solar declination is at around 9:00 my time?  (6 hours and 55 minutes before the actual equinox).  I wonder if I'll be able to detect this small amount?
 
Thanks 
John
 
John L. Carmichael Jr.
Sundial Sculptures
925 E. Foothills Dr.
Tucson Arizona 85718
USA
 
Tel: 520-696-1709
Email: [EMAIL PROTECTED]
Website: <http://www.sundialsculptures.com>

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