| day_night {photobiology} | R Documentation |
Functions for calculating the timing of solar positions by means of function
sun_angles, given geographical coordinates and dates. They can be also
used to find the time for an arbitrary solar elevation between 90 and -90
degrees by supplying "twilight" angle(s) as argument.
day_night(date = lubridate::now(tzone = "UTC"), tz = lubridate::tz(date), geocode = data.frame(lon = 0, lat = 51.5, address = "Greenwich"), twilight = "none", unit.out = "hours") day_night_fast(date, tz, geocode, twilight, unit.out) noon_time(date = lubridate::today(), tz = Sys.timezone(), geocode = data.frame(lon = 0, lat = 51.5, address = "Greenwich"), twilight = "none", unit.out = "datetime") sunrise_time(date = lubridate::today(), tz = Sys.timezone(), geocode = data.frame(lon = 0, lat = 51.5, address = "Greenwich"), twilight = "sunlight", unit.out = "datetime") sunset_time(date = lubridate::today(), tz = Sys.timezone(), geocode = data.frame(lon = 0, lat = 51.5, address = "Greenwich"), twilight = "sunlight", unit.out = "datetime") day_length(date = lubridate::now(), tz = "UTC", geocode = data.frame(lon = 0, lat = 51.5, address = "Greenwich"), twilight = "sunlight", unit.out = "hours") night_length(date = lubridate::now(), tz = "UTC", geocode = data.frame(lon = 0, lat = 51.5, address = "Greenwich"), twilight = "sunlight", unit.out = "hours")
date |
"vector" of POSIXct times or Date objects, any valid TZ is allowed, default is current date |
tz |
character vector indicating time zone to be used in output. |
geocode |
data frame with one or more rows and variables lon and lat as numeric values (degrees). If present, address will be copied to the output. |
twilight |
character string, one of "none", "civil", "nautical",
"astronomical", or a |
unit.out |
character string, One of "datetime", "day", "hour", "minute", or "second". |
Twilight names are interpreted as follows. "none": solar elevation =
0 degrees. "refraction": solar elevation = 0 degrees + refraction
correction. "sunlight": upper rim of solar disk corrected for refraction.
"civil": -6 degrees, "naval": -12 degrees, and "astronomical": -18 degrees.
Unit names for output are as follows: "hours" times for sunrise and sunset
are returned as times-of-day in hours since midnight. "date" or "datetime"
return the same times as datetime objects with TZ set (this is much slower
than the "hours"). Day length and night length are returned as numeric
values expressed in hours when ‘"datetime"’ is passed as argument to
unit.out. If twilight is a numeric vector of length two,
the element with index 1 is used for sunrise and that with index 2 for
sunset.
A data.frame with variables day, tz, twilight.rise, twilight.set,
longitude, latitude, address, sunrise, noon, sunset, daylength,
nightlength.
noon_time, sunrise_time and sunset_time return a
vector of POSIXct times
day_length and night_length return numeric a vector
giving the length in hours
Be aware that R's Date class does not save time zone
metadata. This can lead to ambiguities in the current implementation as
based on time instants. The argument passed to date should be
of class POSIXct, in other words an instant in time, from which
the correct date will be computed based on the tz argument.
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 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.
night_length returns the length of night-time conditions in one
day (00:00:00 to 23:59:59), rather than the length of the night between two
consecutive days.
Other astronomy related functions: format.solar_time,
is.solar_time,
print.solar_time, solar_time,
sun_angles
library(lubridate)
my.geocode <- data.frame(lat = 60, lon = 25)
day_night(ymd("2015-05-30"), geocode = my.geocode)
day_night(ymd("2015-05-30") + days(1:10), geocode = my.geocode, twilight = "civil")
sunrise_time(ymd("2015-05-30"), geocode = my.geocode)
noon_time(ymd("2015-05-30"), geocode = my.geocode)
sunset_time(ymd("2015-05-30"), geocode = my.geocode)
day_length(ymd("2015-05-30"), geocode = my.geocode)
day_length(ymd("2015-05-30"), geocode = my.geocode, unit.out = "day")