sunAngle {oce} | R Documentation |
Solar angle as function of space and time.
sunAngle(t, longitude = 0, latitude = 0, useRefraction = FALSE)
t |
time, a POSIXt object (converted to timezone |
longitude |
observer longitude in degrees east |
latitude |
observer latitude in degrees north |
useRefraction |
boolean, set to |
Based on NASA-provided Fortran program, in turn (according to comments in the code) based on "The Astronomical Almanac".
A list containing the following.
time |
time |
azimuth |
azimuth, in degrees eastward of north, from 0 to 360. (See diagram below.) |
altitude |
altitude, in degrees above the horizon, ranging from -90 to 90. (See diagram below.) |
diameter |
solar diameter, in degrees |
distance |
distance to sun, in astronomical units |
Dan Kelley
Based on Fortran code retrieved from ftp://climate1.gsfc.nasa.gov/wiscombe/Solar_Rad/SunAngles/sunae.f on 2009-11-1. Comments in that code list as references:
Michalsky, J., 1988: The Astronomical Almanac's algorithm for approximate solar position (1950-2050), Solar Energy 40, 227-235
The Astronomical Almanac, U.S. Gov't Printing Office, Washington, D.C. (published every year).
The code comments suggest that the appendix in Michalsky (1988) contains errors, and declares the use of the following formulae in the 1995 version the Almanac:
p. A12: approximation to sunrise/set times;
p. B61: solar altitude (AKA elevation) and azimuth;
p. B62: refraction correction;
p. C24: mean longitude, mean anomaly, ecliptic longitude, obliquity of ecliptic, right ascension, declination, Earth-Sun distance, angular diameter of Sun;
p. L2: Greenwich mean sidereal time (ignoring T^2, T^3 terms).
The code lists authors as Dr. Joe Michalsky and Dr. Lee Harrison (State University of New York), with modifications by Dr. Warren Wiscombe (NASA Goddard Space Flight Center).
The equivalent function for the moon is moonAngle
.
Other things related to astronomy: eclipticalToEquatorial
,
equatorialToLocalHorizontal
,
julianCenturyAnomaly
,
julianDay
, moonAngle
,
siderealTime
rise <- as.POSIXct("2011-03-03 06:49:00", tz="UTC") + 4*3600 set <- as.POSIXct("2011-03-03 18:04:00", tz="UTC") + 4*3600 mismatch <- function(lonlat) { sunAngle(rise, lonlat[1], lonlat[2])$altitude^2 + sunAngle(set, lonlat[1], lonlat[2])$altitude^2 } result <- optim(c(1,1), mismatch) lon.hfx <- (-63.55274) lat.hfx <- 44.65 dist <- geodDist(result$par[1], result$par[2], lon.hfx, lat.hfx) cat(sprintf("Infer Halifax latitude %.2f and longitude %.2f; distance mismatch %.0f km", result$par[2], result$par[1], dist))