sdxEOT Function

Description

Returns the Solar Equation of Time in degrees for a given point in time.

Syntax

sdxEOT(timex)

timex

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

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.

All MJD and SDY values are expressed in UT. A <TimeZone> appended to the time value is informational only and doesn't affect the time value.

The sdMJDx and sdSDYx functions may be used to create time values usable by this function.

Return Values

sdxEOT returns a double precision number. The Solar Equation of Time varies on an annual cycle. The minimum value is approximately -3.75 degrees, the maximum +4.2 degrees.

A positive EOT means that True Solar Time is ahead of Mean (Clock) Solar Time.

If timex is a

MJD time value	The function returns a value for that point in world history.
SDY time value	The function returns a "least error"/ "average value" optimised for the years 2000 to 2100. How?

Remarks

Solar Equation of Time is calculated using algorithms published in Meeus, Jean. "Astronomical Algorithms" 2nd Ed., Willmann-Bell.

You can convert a degree value to it's Degrees:Minute:Seconds components using the sdDUnpackx function and to a printable text format using sdD2Text function.

Example

What is the Solar Equation of Time at MJD 52448.125 (3am UT, June 23rd, 2002) :
sdxEOT("<MJD>52448.125</MJD>") equals -0.5157 degrees

And converted to minutes:
sdD2Unit(sdxEOT("<MJD>52448.125</MJD>"),sdUnitTMin) equals -2.0628 minutes.

What is the Solar Equation of Time at 6am, 21st January, 2001 Amsterdam time?:
    Amsterdam's timezone is -1
    sdxEOT(sdMJDx(2001,1,21,6,0,0,-1)) equals -2.8175 degrees.

And converted to minutes:
    sdD2Unit(sdxEOT(sdMJDx(2001,1,21,6,0,0,-1)),sdUnitTMin)equals -11.2700 minutes.

What is the Solar Equation of Time for the point on a projection sundial to show 6am, 21st January in Amsterdam?:
    Amsterdam's timezone is -1
    We will use the Solar Day of Year timescale as this is year independent.
    sdxEOT(sdSDYx(1,21,6,0,0,-1)) equals -2.7909 degrees

And converting to minutes:
    sdD2Unit(sdxEOT(sdSDYx(1,21,6,0,0,-1)),sdUnitTMin) equals -11.1636 minutes.