R: Solar Angle as Function of Space and Time

sunAngle {oce} | R Documentation

## Solar Angle as Function of Space and Time

### Description

Solar angle as function of space and time.

### Usage

    sunAngle(t, longitude = 0, latitude = 0, useRefraction = FALSE)

### Arguments

`t` | Time, a POSIXt object (must be in timezone UTC), or a numeric value that corresponds to such a time.
`longitude` | observer longitude in degrees east
`latitude` | observer latitude in degrees north
`useRefraction` | boolean, set to `TRUE` to apply a correction for atmospheric refraction

### Details

Based on NASA-provided Fortran program, in turn (according to comments in the code) based on "The Astronomical Almanac".

### Value

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

### Author(s)

Dan Kelley

### References

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).

### See Also

The equivalent function for the moon is `moonAngle`.

Other things related to astronomy: `eclipticalToEquatorial`, `equatorialToLocalHorizontal`, `julianCenturyAnomaly`, `julianDay`, `moonAngle`, `siderealTime`

### Examples

    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))

[Package oce version 0.9-20 Index]