astronomyengine (version 0.1.0)

astro_observer_state: Observer position and velocity vector from geographic coordinates

Description

Calculates the geocentric equatorial position and velocity vectors of an observer on the surface of the Earth, taking into account the Earth's rotation.

Usage

astro_observer_state(time, latitude, longitude, height, of_date = FALSE)

Value

A list with components:

x

Equatorial x-coordinate in AU

y

Equatorial y-coordinate in AU

z

Equatorial z-coordinate in AU

vx

Equatorial x-velocity in AU/day

vy

Equatorial y-velocity in AU/day

vz

Equatorial z-velocity in AU/day

t

The time (POSIXct) at which the state vector is valid

status

Status code (0 = success)

The position vector components are expressed in Astronomical Units (AU). Multiply by #KM_PER_AU to convert to kilometers. The velocity components are in AU per day.

If only position is needed without velocity, astro_observer_vector() is slightly more efficient.

Arguments

time

A POSIXct date and time for which to calculate the observer's state vector.

latitude

The geographic latitude of the observer in degrees north of the equator (range: -90 to +90).

longitude

The geographic longitude of the observer in degrees east of the prime meridian (range: 0 to 360 or -180 to +180).

height

The elevation of the observer above sea level in meters.

of_date

Logical. If TRUE, uses equator-of-date coordinates (Earth's equator at the given time). If FALSE (default), uses J2000 coordinates (Earth's equator on 2000-01-01).

Examples

# Get observer state at Sydney Observatory
time <- as.POSIXct("2024-01-01 12:00:00", tz = "UTC")
obs_state <- astro_observer_state(time, latitude = -33.8688, longitude = 151.2093, height = 0)
obs_state