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 given UTC time (Coordinated Universal Time between year 0 and 3000) 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

u_corrected - the corrected angular position of the satellite in degrees, used to determine visibility conditions (whether a moon can be seen against Jupiter's disk or is hidden behind it)

Usage

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

Arguments

year: Type in the year (integer number from 0 to 3000).
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 4 variables: $ moon : chr "Io" "Europa" "Ganymede" "Callisto" $ x : num $ y : num $ u_corrected: num Four rows - each row has the position (x,y) and corrected angular position (u_corrected) 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 u_corrected
#> 1       Io   2.802832  0.1370436    151.7898
#> 2   Europa  -8.908685  0.0772815    251.6987
#> 3 Ganymede   7.529880 -0.3393067     30.2019
#> 4 Callisto -24.999085  0.2351669    250.2692
# Also try these interesting configuration moments:
galsat(2021, 8, 15, 15, 48)

#>       moon          x           y u_corrected
#> 1       Io  0.9797847  0.07917838  170.411403
#> 2   Europa -0.7906981 -0.12661976  355.127268
#> 3 Ganymede -0.6605975 -0.20468771  357.477237
#> 4 Callisto  0.8873500 -0.36182567    1.917545
galsat(2032, 1, 5, 6, 44)

#>       moon           x          y u_corrected
#> 1       Io  0.22409172 -0.1877863    177.8303
#> 2   Europa -8.19592931 -0.1487233    240.2495
#> 3 Ganymede  0.06620236 -0.4752985    179.7466
#> 4 Callisto -0.43339665 -0.8370223    180.9418
galsat(2033, 7, 28, 4, 50)

#>       moon          x          y u_corrected
#> 1       Io  0.1130089  0.1120284  178.899094
#> 2   Europa  0.2794994 -0.1772460    1.720653
#> 3 Ganymede  0.8199864 -0.2855337    3.131382
#> 4 Callisto -0.4619301  0.4992523  181.009789
galsat(2039, 7, 31, 18, 55)

#>       moon          x             y u_corrected
#> 1       Io  0.8650198 -0.0821923525   171.54352
#> 2   Europa  0.4450186 -0.1338542538   177.31099
#> 3 Ganymede 14.9887339 -0.0006076166    90.16442
#> 4 Callisto -1.1553599 -0.3741162112   182.49804