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Convert UTC time to solar time

Source: R/convert_UTC_to_solartime.R
convert_UTC_to_solartime.Rd

Converts a UTC datetime to mean or apparent solar time for a given longitude. Uses a high-precision offset for longitude and applies the equation of time for apparent solar time.

Usage

convert_UTC_to_solartime(
  date.time,
  longitude,
  time.type = c("mean solar", "apparent solar")
)

Arguments

date.time

POSIXct vector in UTC.

longitude

Numeric longitude in decimal degrees. Western longitudes are negative.

time.type

One of "mean solar" (default) or "apparent solar".

Value

A POSIXct datetime in mean or apparent solar time (still tz = "UTC").

Details

Apparent solar time, or true solar time, is noon when the sun is at its zenith. Mean solar time approximates apparent solar time but keeps noons exactly 24 hours apart. Elsewhere in this package, variables named solar.time are mean solar time.

Examples

utc <- as.POSIXct("2025-04-30 12:00:00", tz = "UTC")
convert_UTC_to_solartime(utc, -90, time.type = "mean solar")
#> [1] "2025-04-30 06:00:59 UTC"
convert_UTC_to_solartime(utc, -90, time.type = "apparent solar")
#> [1] "2025-04-30 06:03:38 UTC"