astro_search_relative_longitude: Search for relative longitude event between Earth and another planet
Description
Searches for the next time when the relative longitude (angle measured in
the ecliptic plane from one planet to another as seen from the Sun) reaches
a specified target angle.
A POSIXct datetime object indicating when the target relative
longitude is reached.
Arguments
body
An integer representing a planet other than Earth (see [astro_body]).
Cannot be the Earth, Moon, or Sun.
target_rel_lon
Numeric. The desired relative longitude in degrees.
Must be in the range [0, 360).
start_time
A POSIXct datetime object specifying when to begin
the search.
Details
Relative longitude defines several important astronomical events:
0°
Conjunction (inferior for Mercury/Venus, opposition for outer planets)
180°
Superior conjunction (planet on opposite side of Sun from Earth)
For planets orbiting closer to the Sun than Earth (Mercury, Venus),
a relative longitude of 0° indicates inferior conjunction.
For planets orbiting farther from the Sun, 0° indicates opposition (closest approach).
# Find next opposition of Mars after 2025-01-01start <- as.POSIXct("2025-01-01", tz = "UTC")
astro_search_relative_longitude(astro_body["MARS"], 0, start)