Topocentric equatorial coordinates of a celestial body — astro

Calculates equatorial coordinates of a celestial body as seen by an observer on Earth's surface.

Usage

astro_equator(
  body,
  time,
  latitude,
  longitude,
  height = 0,
  equdate = FALSE,
  aberration = TRUE
)

Arguments

body: Identifier of celestial body (e.g., astro_body[["SUN"]], astro_body[["MARS"]]). Must not be the Earth.
time: A POSIXct time value.
latitude: Observer's geographic latitude in degrees (positive north).
longitude: Observer's geographic longitude in degrees (positive east).
height: Observer's height in meters above sea level.
equdate: One of TRUE (true-equator-of-date) or FALSE (J2000). Default is FALSE.
aberration: One of TRUE (correct for aberration) or FALSE. Default is TRUE.

Value

A list with elements:

ra: Right ascension in sidereal hours.
dec: Declination in degrees.
dist: Distance in AU.

Details

This function corrects for light travel time and topocentric parallax (the angular shift depending on the observer's location on Earth). Parallax correction is most significant for the Moon but has a small effect on other bodies.

Examples

time <- as.POSIXct("2025-02-19 22:10:12", tz = "UTC")
astro_equator(astro_body[["MARS"]], time, latitude = -33.87, longitude = 151.21)
#> $ra
#> [1] 7.247414
#> 
#> $dec
#> [1] 26.17006
#> 
#> $dist
#> [1] 0.7930461
#>