sunpos: Compute the Right Ascension and Declination of the Sun at...
In astrolibR: Astronomy Users Library

Description Usage Arguments Details Value Author(s) See Also Examples

Compute the Right Ascension and Declination of the Sun at specified Julian date(s)

1	sunpos(jd, radian=F)

`jd`	Julian ephemeris date, scalar or vector
`radian`	if =TRUE, then all output variables are given in radians rather than degrees (default=FALSE)

This function uses a truncated version of Newcomb's Sun http://en.wikipedia.org/wiki/Newcomb's_Tables_of_the_Sun. The returned RA and Dec are in the given date's equinox.

Patrick Wallace (Rutherford Appleton Laboratory, UK) has tested the accuracy of a C adaptation of the IDL sunpos.pro code and found the following results. From 1900-2100 sunpos gave 7.3 arcsec maximum error, 2.6 arcsec RMS. Over the shorter interval 1950-2050 the figures were 6.4 arcsec max, 2.2 arcsec RMS.

`ra`	apparent right ascension of the Sun, referred to the true equator of the specified date(s), in degrees
`dec`	declination of the Sun, in degrees
`elong`	ecliptic longitude of the Sun, in degrees
`obliquity`	obliquity of the ecliptic, in degrees

FORTRAN routine by B. Emerson (RGO); IDL version by Michael R. Greason, STX, 1988

R adaptation by Arnab Chakraborty June 2013

cirrange nutate polyidl ten

# Find the apparent RA and Dec of the Sun on May 1, 1982
# Result:  02 31 32.61  +14 54 34.9 
# The Astronomical Almanac gives 02 31 32.58 +14 54 34.9,
# so the error in sunpos for this case is < 0.5".
       
jd = jdcnv(1982, 5, 1,0)      # Find Julian date jd = 2445090.5   
out = sunpos(jd)  

  
# Plot the apparent declination of the Sun for every day in 1997

jd = jdcnv(1997,1,1,0)  # Julian date on Jan 1, 1997
days = seq(0,365)  
plot(days, sunpos(jd+days)$dec, type='b', pch=20, lwd=2)