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Sunlit Design > The Sun API > Documentation > sdxFindAnnFeatx Function


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sdxFindAnnFeatx Function

Description

Returns a time value for an annually occurring solar event.  Annual Features supported include the eqinoxes, solstices and the maxima, minima and zero crossings of Declination and Equation of Time.

Syntax

sdxFindAnnFeatx(timex, annualfeature)

timex   

A String; Modified Julian Day (MJD) or Solar Day of Year (SDY) time value.

annualfeature     a constant value showing which annual feature to find.


Time Value Formats

MJD Time Value

"<MJD> nnn </MJD>"
"<MJD> nnn </MJD><TimeZone> tz </TimeZone>"

See sdMJDx function.
SDY Time Value

"<SDY> nnn </SDY>"
"<SDY> nnn </SDY><TimeZone> tz </TimeZone>"

See sdSDYx function.

Return Values

sdxFindAnnFeatx returns an XML string MJD or SDY time value.

If timex is a

MJD time value     The function extracts the year from the MJD time value and then finds the time of the requested feature in that year.  

The returned value is of the format:

"nnn <MJD> nnn </MJD>"

If the MJD time value has a TimeZone then the following is returned:

"nnn <MJD>nnn</MJD> <TimeZone>tz</TimeZone>"

SDY time value The function returns a "least error"/ "average value" time value for this annual feature optimised for the next 100 years. How?

The returned value is of the format:

"nnn <SDY> nnn </SDY>"

If the SDY time value has a TimeZone then the following is returned:

"nnn <SDY>nnn</SDY> <TimeZone>tz</TimeZone>"

Remarks

The following table generated with The Sun API matches the U.S. Naval observatory's values exactly. Compare the table below with:

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

2000 Equinoxes March 20 07:35:21.4770 [UT] September 22 17:27:35.9507 [UT]
Solstices June 21 01:47:46.2446 [UT] December 21 13:37:31.1415 [UT]
2001 Equinoxes March 20 13:30:52.6748 [UT] September 22 23:04:30.6638 [UT]
Solstices June 21 07:37:54.4232 [UT] December 21 19:21:30.7143 [UT]
2002 Equinoxes March 20 19:16:15.1619 [UT] September 23 04:55:25.2033 [UT]
Solstices June 21 13:24:22.2168 [UT] December 22 01:14:30.2728 [UT]
2003 Equinoxes March 21 00:59:53.8487 [UT] September 23 10:46:51.5557 [UT]
Solstices June 21 19:10:20.1759 [UT] December 22 07:03:46.4641 [UT]
2004 Equinoxes March 20 06:48:36.7287 [UT] September 22 16:29:49.0017 [UT]
Solstices June 21 00:56:48.7443 [UT] December 21 12:41:32.0381 [UT]

Example

Find the time UT of the March Equinox in 2001:

    sdxfindannfeatx(sdMJDx(2001,6,1,0,0,0,0),sdFeatEquinoxMar)

equals "51988.5631096615<MJD>51988.5631096615</MJD>
                                                         <TimeZone>0</TimeZone>"

Which when turned into a printable string using the sdxTime2Text function:

equals: 2001/03/20 13:30:52.6748 [UT]