Calculate & draw the positions of the Galilean satellites

galsat() is used to determine the positions of the four greatest satellites of Jupiter (called Galilean satellites). Positions are shown on the plot for any given time (ET – Ephemeris Time) with respect to the planet, as seen from the Earth.

The galsat() function returns numerical values of the satellites’ positions:

x – the apparent rectangular coordinate of the satellite with respect to the center of Jupiter’s disk in the equatorial plane in the units of Jupiter’s equatorial radius; X is positive toward the west

y – the apparent rectangular coordinate of the satellite with respect to the center of Jupiter’s disk from the equatorial plane in the units of Jupiter’s equatorial radius; Y is positive toward the north

Usage

galsat(year, month, day, hour, minute)

Arguments

year: Type in the year (integer number greater then or equal 0).
month: Type in the month (integer number from 1 to 12).
day: Type in the day (integer number from 1 to 31).
hour: Type in the hour (integer number from 0 to 23).
minute: Type in the minute (integer number from 0 to 59).

Value

data.frame: 4 observations of 3 variables: $ moon: chr "Io" "Europa" "Ganymede" "Callisto" $ x : num $ y : num Four rows - each row has the position (x,y) of one moon. Additionally, the positions of the moons are shown graphically.

Details

The function is based on algorithms in the book: Astronomical Formulae for Calculators (4th edition), Jean Meeus, Willmann-Bell Inc., 1988

Examples

galsat(2025, 10, 13, 23, 30)

#>       moon          x           y
#> 1       Io   2.815596  0.13686317
#> 2   Europa  -8.904947  0.07756843
#> 3 Ganymede   7.521977 -0.33942777
#> 4 Callisto -24.996779  0.23533560