Sun Declination and Right Ascension

The formulae are from Meeus (1991), chapter 24 (which uses chapter 21).

Usage

sunDeclinationRightAscension(time, apparent = FALSE)

Arguments

time

a POSIXct time. This ought to be in UTC timezone; if not, the behaviour of this function is unlikely to be correct.

apparent

logical value indicating whether to return the 'apparent' angles.

Value

A list containing declination and rightAscension, in degrees.

References

• Meeus, Jean. Astronomical Algorithms. Second Edition. Richmond, Virginia, USA: Willmann-Bell, 1991.

See also

Other things related to astronomy: angle2hms(), eclipticalToEquatorial(), equatorialToLocalHorizontal(), julianCenturyAnomaly(), julianDay(), moonAngle(), siderealTime(), sunAngle()

Author

Dan Kelley, based on formulae in Meeus (1991).

Examples

# Example 24.a in Meeus (1991) (page 158 PDF, 153 print)
time <- as.POSIXct("1992-10-13 00:00:00", tz = "UTC")
a <- sunDeclinationRightAscension(time, apparent = TRUE)
stopifnot(abs(a$declination - (-7.78507)) < 0.00004)
stopifnot(abs(a$rightAscension - (-161.61919)) < 0.00003)
b <- sunDeclinationRightAscension(time)
# check against previous results, to protect aginst code-drift errors
stopifnot(abs(b$declination - (-7.785464443)) < 0.000000001)
stopifnot(abs(b$rightAscension - (-161.6183305)) < 0.0000001)