Calculates the apparent location of a body relative to the local horizon of an observer on Earth.
Arguments
- time
A POSIXct time value.
- latitude
Observer's geographic latitude in degrees (positive north).
- longitude
Observer's geographic longitude in degrees (positive east).
- ra
Right ascension of the body in sidereal hours.
- dec
Declination of the body in degrees.
- refraction
One of
"REFRACTION_NORMAL","REFRACTION_JPLHOR", or"REFRACTION_NONE".
Value
A list with elements:
- azimuth
Azimuth angle in degrees (eastward from north).
- altitude
Altitude angle in degrees (positive above horizon).
- ra
Right ascension of the body in sidereal hours.
- dec
Declination of the body in degrees.
Details
Given a date, time, geographic location, and equatorial coordinates of a celestial body, this function returns horizontal coordinates (azimuth and altitude) relative to the horizon.
The ra and dec must be equator-of-date coordinates. Equator-of-date coordinates can be
obtained by calling astro_equator() with equdate = "EQUATOR_OF_DATE" and
aberration = "ABERRATION".
Atmospheric refraction correction is recommended. Pass refraction = "REFRACTION_NORMAL"
to correct for optical lensing of the Earth's atmosphere that causes objects to appear
higher above the horizon than they actually are.
Examples
time <- as.POSIXct("2025-02-19 22:10:12", tz = "UTC")
astro_horizon(time, latitude = -33.87, longitude = 151.21, ra = 10.5, dec = -20.0)
#> $azimuth
#> [1] 238.4689
#>
#> $altitude
#> [1] -8.969315
#>
#> $ra
#> [1] 10.5
#>
#> $dec
#> [1] -20
#>