R: Solar angles

sun_angles {photobiology} | R Documentation

## Solar angles

### Description

This function returns the solar angles for a given time and location.

### Usage

    sun_angles(time = lubridate::now(tzone = "UTC"), tz = lubridate::tz(time),
      geocode = data.frame(lon = 0, lat = 51.5, address = "Greenwich"),
      use.refraction = FALSE)

    sun_angles_fast(time, tz, geocode, use.refraction)

    sun_elevation(time = lubridate::now(), tz = lubridate::tz(time),
      geocode = data.frame(lon = 0, lat = 51.5, address = "Greenwich"),
      use.refraction = FALSE)

    sun_zenith_angle(time = lubridate::now(), tz = lubridate::tz(time),
      geocode = data.frame(lon = 0, lat = 51.5, address = "Greenwich"),
      use.refraction = FALSE)

    sun_azimuth(time = lubridate::now(), tz = lubridate::tz(time),
      geocode = data.frame(lon = 0, lat = 51.5, address = "Greenwich"),
      use.refraction = FALSE)

### Arguments

`time` | A "vector" of POSIXct Time, with any valid time zone (TZ) is allowed, default is current time.
`tz` | character string indicating time zone to be used in output.
`geocode` | data frame with variables lon and lat as numeric values (degrees), nrow > 1, allowed.
`use.refraction` | logical Flag indicating whether to correct for fraction in the atmosphere.

### Value

A data.frame with variables time (in same TZ as input), TZ, solartime, longitude, latitude, address, azimuth, and elevation. If a data frame with multiple rows is passed to `geocode` and a vector of times longer than one is passed to `time`, sun position for all combinations of locations and times are returned are returned by `sun_angles`. In contrast, convenience functions returning a vector, require that either a single time instant or a single location are supplied—i.e. only one of these two arguments can be vectorized in a given call.

### Note

This function is an implementation of Meeus equations as used in NOAAs on-line web calculator, which are very precise and valid for a very broad range of dates. For the times of sunrise and sunset the times are affected by refraction in the atmosphere, which does in turn depend on weather conditions. The effect of refraction on the apparent position of the sun is only an estimate based on "typical" conditions. The more tangential to the horizon is the path of the sun, the larger the effect of refraction is on the times of visual occlusion of the sun behind the horizon—i.e. the largest timing errors occur at high latitudes. The computation is not defined for latitudes 90 and -90 degrees, i.e. at the poles. There exists a different R implementation of the same algorithms called "AstroCalcPureR" available as function `astrocalc4r` in package 'fishmethods'. Although the equations used are almost all the same, the function signatures and which values are returned differ. In particular, the present implementation splits the calculation into two separate functions, one returning angles at given instants in time, and a separate one returning the timing of events for given dates.

### See Also

Other astronomy related functions: `day_night`, `format.solar_time`, `is.solar_time`, `print.solar_time`, `solar_time`

### Examples

    library(lubridate)
    sun_angles()
    sun_azimuth()
    sun_elevation()
    sun_zenith_angle()
    sun_angles(ymd_hms("2014-09-23 12:00:00"))
    sun_angles(ymd_hms("2014-09-23 12:00:00"),
               geocode = data.frame(lat=60, lon=0))
    sun_angles(ymd_hms("2014-09-23 12:00:00") + minutes((0:6) * 10))

[Package photobiology version 0.9.21 Index]