Search for lunar apsis events — search_lunar

Finds the date and time of the Moon's closest distance (perigee) or farthest distance (apogee) with respect to the Earth after a given start time.

Usage

search_lunar_apsis(start_time)

Arguments

start_time: A POSIXct datetime object indicating when to start the search.

Value

A list containing:

time: A POSIXct datetime of the next lunar apsis.
kind: Integer code: 0 for perigee (APSIS_PERICENTER), 1 for apogee (APSIS_APOCENTER).
dist_au: Distance in astronomical units.
dist_km: Distance in kilometers.

Details

The closest point is called perigee and the farthest point is called apogee. The word apsis refers to either event.

To iterate through consecutive alternating perigee and apogee events, call search_lunar_apsis() once, then use the return value to call next_lunar_apsis(). After that, keep feeding the previous return value from next_lunar_apsis() into another call of next_lunar_apsis() as many times as desired.

Examples

start <- as.POSIXct("2025-01-01", tz = "UTC")
apsis <- search_lunar_apsis(start)
apsis$time
#> [1] "2025-01-07 23:58:50 UTC"
apsis$kind
#> [1] 0