Some simple steps to do calculations

To compute the position of celestial body or star with SE (Swiss Ephemeris), you do the following steps:

First loadswephR:

library(swephR)

Optionally set the directory path of the ephemeris files (the format of the path depends on your OS), e.g.:

swe_set_ephe_path("C:\\sweph\\ephe")

For a specific date, compute the Julian day number (in below example: J2000.0, 1 January 2000 at 12:00 UT):

year <-2000month <-1day <-1hour <-12jdut <-swe_julday(year, month, day, hour, SE$GREG_CAL)jdut#> [1] 2451545

Compute (using Moshier ephemeris) the positions (longitude, latitude, distance, longitude speed and latitude speed) of a planet or other celestial bodies (in below example: the Sun):

ipl <-SE$SUNiflag <-SE$FLG_MOSEPH+SE$FLG_SPEEDresult <-swe_calc_ut(jdut, ipl, iflag)result#> $return#> [1] 260#>#> $xx#> [1]  2.803689e+02  2.323265e-04  9.833276e-01  1.019432e+00 -8.922802e-07#> [6] -7.339410e-06#>#> $serr#> [1] ""

or a fixed star (in below example: Sirius):

starname = "sirius"result <-swe_fixstar2_ut(starname, jdut, iflag)result#> $return#> [1] 260#>#> $starname#> [1] "Sirius,alCMa"#>#> $xx#> [1]  1.040853e+02 -3.960507e+01  5.439322e+05  4.643164e-05 -7.119376e-05#> [6] -4.130539e-03#>#> $serr#> [1] ""

Determine the Julian day number of the Heliacal Rise of Sirius:

options(digits=15)result <-swe_heliacal_ut(jdut,c(0,50,10),c(1013.25,15,50,0.25),c(25,1,1,1,5,0.8),starname,  SE$HELIACAL_RISING,SE$HELFLAG_HIGH_PRECISION+SE$FLG_MOSEPH)result#> $return#> [1] 0#>#> $dret#>  [1] 2451779.67915537 2451779.68432898 2451779.69042851       0.00000000#>  [5]       0.00000000       0.00000000       0.00000000       0.00000000#>  [9]       0.00000000       0.00000000       0.00000000       0.00000000#> [13]       0.00000000       0.00000000       0.00000000       0.00000000#> [17]       0.00000000       0.00000000       0.00000000       0.00000000#> [21]       0.00000000       0.00000000       0.00000000       0.00000000#> [25]       0.00000000       0.00000000       0.00000000       0.00000000#> [29]       0.00000000       0.00000000       0.00000000       0.00000000#> [33]       0.00000000       0.00000000       0.00000000       0.00000000#> [37]       0.00000000       0.00000000       0.00000000       0.00000000#> [41]       0.00000000       0.00000000       0.00000000       0.00000000#> [45]       0.00000000       0.00000000       0.00000000       0.00000000#> [49]       0.00000000       0.00000000#>#> $serr#> [1] ""

Here is a miniature sample program described in Chapter 0 of the programmer’s manual of SE (see also):

options(digits=6)swe_set_ephe_path(NULL)  iflag =SE$FLG_SPEED+SE$FLG_MOSEPH  {#get year    jyear <-2000#get month    jmon <-1#get day    jday <-1#get time    jhour <-12#determine julian day number (at 12:00 GMT)    tjd_ut <-swe_julday(jyear, jmon, jday, jhour, SE$GREG_CAL)cat("Julian day number (UT) :", tjd_ut,"(",jyear,",",jmon,",",jday,"; proleptic Gregorian calendar)\n")cat("planet :",c("longitude","latitude","distance","long. speed","lat. speed"),"\n")cat("===========================================================\n")# loop over all planetsfor (pin SE$SUN:SE$OSCU_APOG) {# get the name of the planet p      objectname =swe_get_planet_name(p)# do the coordinate calculation for this planet p        i =swe_calc_ut(tjd_ut, p, iflag)if (i$return<0) {cat("Error :", i$err,"(", objectname,")\n")        }else        {# print datacat (objectname,":", i$xx[0:5],"\n")        }    }  }#> Julian day number (UT) : 2451545 ( 2000 , 1 , 1 ; proleptic Gregorian calendar)#> planet : longitude latitude distance long. speed lat. speed#> ===========================================================#> Sun : 280.369 0.000232327 0.983328 1.01943 -8.9228e-07#> Moon : 223.324 5.17082 0.00268998 12.0212 -0.178063#> Mercury : 271.889 -0.994825 1.41547 1.55625 -0.0974918#> Venus : 241.566 2.06635 1.13758 1.20904 -0.0280736#> Mars : 327.963 -1.06778 1.84969 0.775673 0.0124755#> Jupiter : 25.253 -1.26217 4.62118 0.0407613 0.00517336#> Saturn : 40.3956 -2.44482 8.6528 -0.0199448 0.00474316#> Uranus : 314.809 -0.658333 20.7272 0.0503436 0.000250014#> Neptune : 303.193 0.234991 31.0245 0.0355701 -0.000223651#> Pluto : 251.455 10.8552 31.0644 0.0351529 0.0014674#> mean Node : 125.041 0 0.00256956 -0.0529518 0#> true Node : 123.953 0 0.00244538 -0.0543822 0#> mean Apogee : 263.464 3.41972 0.00271063 0.111328 -0.011021#> osc. Apogee : 252.979 4.07551 0.00271384 1.64684 -0.0971172

At the end of your computations close all files and free up memory:

swe_close()

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swephR

Victor Reijs

2025-03-29

Some simple steps to do calculations