solar_time: Local solar time

In photobiology: Photobiological Calculations

Description

solar_time computes from a time and geocode, the time of day expressed in seconds since midnight. solar_date returns the same instant in time as a date-time object. Solar time is useful when we want to plot data according to the local solar time of day, irrespective of the date. Solar date is useful when we want to plot a time series stretching for several days using the local solar time but distinguishing between days.

Usage

solar_time(time = lubridate::now(), geocode = data.frame(lon = 0, lat =
  51.5, address = "Greenwich"), unit.out = "time")

Arguments

time	POSIXct Time, any valid time zone (TZ) is allowed, default is current time
geocode	data frame with variables lon and lat as numeric values (degrees).
unit.out	character string, One of "datetime", "hour", "minute", or "second".

Value

For solar_time() numeric value in seconds from midnight but with an additional class attribute "solar.time".

Warning!

Returned values are computed based on the time zone of the argument for parameter time. In the case of solar time, this timezone does not affect the result. However, in the case of solar dates the date part may be off by one day, if the time zone does not match the coordinates of the geocode value provided as argument.

Note

The algorithm is approximate, it calculates the difference between local solar noon and noon in the time zone of time and uses this value for the whole day when converting times into solar time. Days are not exactly 24 h long. Between successive days the shift is only a few seconds, and this leads to a small jump at midnight.

See Also

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

Examples

# BA.geocode <- ggmap::geocode("Buenos Aires, Argentina")
BA.geocode <- data.frame(lon = -58.38156, lat = -34.60368)
sol_t <- solar_time(lubridate::dmy_hms("21/06/2016 10:00:00", tz = "UTC"),
                    BA.geocode)
sol_t
class(sol_t)

sol_d <- solar_time(lubridate::dmy_hms("21/06/2016 10:00:00", tz = "UTC"),
                    BA.geocode,
                    unit.out = "datetime")
sol_d
class(sol_d)

photobiology documentation built on April 3, 2018, 1:06 a.m.