photobiology (version 0.11.4)

day_night: Times for sun positions

Description

Functions for calculating the timing of solar positions, 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.

Usage

day_night(
  date = lubridate::now(tzone = "UTC"),
  tz = ifelse(lubridate::is.Date(date), "UTC", lubridate::tz(date)),
  geocode = tibble::tibble(lon = 0, lat = 51.5, address = "Greenwich"),
  twilight = "none",
  unit.out = "hours"
)
day_night_fast(date, tz, geocode, twilight, unit.out)
is_daytime(
  date = lubridate::now(tzone = "UTC"),
  tz = ifelse(lubridate::is.Date(date), "UTC", lubridate::tz(date)),
  geocode = tibble::tibble(lon = 0, lat = 51.5, address = "Greenwich"),
  twilight = "none",
  unit.out = "hours"
)
noon_time(
  date = lubridate::now(tzone = "UTC"),
  tz = lubridate::tz(date),
  geocode = tibble::tibble(lon = 0, lat = 51.5, address = "Greenwich"),
  twilight = "none",
  unit.out = "datetime"
)
sunrise_time(
  date = lubridate::now(tzone = "UTC"),
  tz = lubridate::tz(date),
  geocode = tibble::tibble(lon = 0, lat = 51.5, address = "Greenwich"),
  twilight = "sunlight",
  unit.out = "datetime"
)
sunset_time(
  date = lubridate::now(tzone = "UTC"),
  tz = lubridate::tz(date),
  geocode = tibble::tibble(lon = 0, lat = 51.5, address = "Greenwich"),
  twilight = "sunlight",
  unit.out = "datetime"
)
day_length(
  date = lubridate::now(tzone = "UTC"),
  tz = "UTC",
  geocode = tibble::tibble(lon = 0, lat = 51.5, address = "Greenwich"),
  twilight = "sunlight",
  unit.out = "hours"
)
night_length(
  date = lubridate::now(tzone = "UTC"),
  tz = "UTC",
  geocode = tibble::tibble(lon = 0, lat = 51.5, address = "Greenwich"),
  twilight = "sunlight",
  unit.out = "hours"
)

Value

A tibble with variables day, tz, twilight.rise, twilight.set, longitude, latitude, address, sunrise, noon, sunset, daylength, nightlength or the corresponding individual vectors.

is_daytime() returns a logical vector, with TRUE for day time and FALSE for night time.

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

Arguments

date

"vector" of POSIXct times orDate objects, any valid TZ is allowed, default is current date at Greenwich matching the default for geocode.

tz

character vector indicating time zone to be used in output and to interpret Date values passed as argument to date.

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", "rim", "refraction", "sunlight", "civil", "nautical", "astronomical", or a numeric vector of length one, or two, giving solar elevation angle(s) in degrees (negative if below the horizon).

unit.out

character string, One of "datetime", "day", "hour", "minute", or "second".

Warning

Be aware that R's Date class does not save time zone metadata. This can lead to ambiguities in the current implementation 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.

The time zone in which times passed to date as argument are expressed does not need to be the local one or match the geocode, however, the returned values will be in the same time zone as the input.

Details

Twilight names are interpreted as follows. "none": solar elevation = 0 degrees. "rim": upper rim of solar disk at the horizon or solar elevation = -0.53 / 2. "refraction": solar elevation = 0 degrees + refraction correction. "sunlight": upper rim of solar disk corrected for refraction, which is close to the value used by the online NOAA Solar Calculator. "civil": -6 degrees, "naval": -12 degrees, and "astronomical": -18 degrees. Unit names for output are as follows: "day", "hours", "minutes" and "seconds" times for sunrise and sunset are returned as times-of-day since midnight expressed in the chosen unit. "date" or "datetime" return the same times as datetime objects with TZ set (this is much slower than "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.

is_daytime() supports twilight specifications by name, a test like sun_elevation() > 0 may be used directly for a numeric angle.

References

The primary source for the algorithm used is the book: Meeus, J. (1998) Astronomical Algorithms, 2 ed., Willmann-Bell, Richmond, VA, USA. ISBN 978-0943396613.

A different implementation is available at https://github.com/NEFSC/READ-PDB-AstroCalc4R/ and in R paclage 'fishmethods'. In 'fishmethods' (= 1.11-0) there is a bug in function astrocalc4r() that affects sunrise and sunset times.

An interactive web page using the same algorithms is available at https://gml.noaa.gov/grad/solcalc/. There are small differences in the returned times compared to our function that seem to be related to the estimation of atmospheric refraction (about 0.1 degrees).

See Also

sun_angles.

Other astronomy related functions: format.solar_time(), sun_angles()

Examples

library(lubridate)

my.geocode <- data.frame(lon = 24.93838,
                         lat = 60.16986,
                         address = "Helsinki, Finland")

day_night(ymd("2015-05-30", tz = "Europe/Helsinki"),
          geocode = my.geocode)
day_night(ymd("2015-05-30", tz = "Europe/Helsinki") + days(1:10),
          geocode = my.geocode,
          twilight = "civil")
sunrise_time(ymd("2015-05-30", tz = "Europe/Helsinki"),
             geocode = my.geocode)
noon_time(ymd("2015-05-30", tz = "Europe/Helsinki"),
          geocode = my.geocode)
sunset_time(ymd("2015-05-30", tz = "Europe/Helsinki"),
            geocode = my.geocode)
day_length(ymd("2015-05-30", tz = "Europe/Helsinki"),
           geocode = my.geocode)
day_length(ymd("2015-05-30", tz = "Europe/Helsinki"),
           geocode = my.geocode,
           unit.out = "day")
is_daytime(ymd("2015-05-30", tz = "Europe/Helsinki") + hours(c(0, 6, 12, 18, 24)),
           geocode = my.geocode)
is_daytime(ymd_hms("2015-05-30 03:00:00", tz = "Europe/Helsinki"),
           geocode = my.geocode)
is_daytime(ymd_hms("2015-05-30 00:00:00", tz = "UTC"),
           geocode = my.geocode)
is_daytime(ymd_hms("2015-05-30 03:00:00", tz = "Europe/Helsinki"),
           geocode = my.geocode,
           twilight = "civil")
is_daytime(ymd_hms("2015-05-30 00:00:00", tz = "UTC"),
           geocode = my.geocode,
           twilight = "civil")