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]