swephR

Victor Reijs

2019-02-09

Some simple steps to do calculations

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

  1. First load swephR and constants used in swephR/SE:
library(swephR)
data(SE)
  1. 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")
  1. For a specific date, compute the Julian day number (in below example: J2000.0, 1 January 2000 at 12:00 UT):
year <- 2000
month <- 1
day <- 1
hour <- 12
jdut <- swe_julday(year, month, day, hour, SE$GREG_CAL)
jdut
#> [1] 2451545
  1. Compute (using Moshier ephemeris) the positions (longitude, latitude, distance, longitude speed and latitude speed) of a planet or other celestial bodies (in below example: the Sun):
ipl <- SE$SUN
iflag <- SE$FLG_MOSEPH + SE$FLG_SPEED
result <- swe_calc_ut(jdut, ipl, iflag)
result
#> $return
#> [1] 260
#> 
#> $xx
#> [1]  2.803689e+02  2.323265e-04  9.833276e-01  1.019432e+00 -8.922491e-07
#> [6] -7.339409e-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  4.329362e-05 -6.562173e-05
#> [6] -4.049452e-03
#> 
#> $serr
#> [1] ""
  1. Determine the Julian day number of the Heliacal Rise of Sirius:
options(digits=15)
result <- swe_heliacal_ut(jdut,c(0,50,10),c(1013.25,15,50,0.25),c(25,1,1,1,5,0.8),starname,
  SE$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
#> 
#> $serr
#> [1] ""
  1. Here is a miniature sample program described in Chapter 0 of the programmer’s manual of SE (see also):
  options(digits=6)
  swe_set_ephe_path(NULL)
  data(SE)
  iflag = SE$FLG_SPEED
  {
    #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$GREG_CAL)
    cat("Julian day number (UT) :", tjd_ut, "(",jyear,",",jmon,",",jday,"; proleptic Gregorian calendar)\n")
    cat("planet :",
        c("longitude", "latitude", "distance", "long. speed", "lat. speed"),
        "\n")
    cat("===========================================================\n")
    # loop over all planets
    for (p in SE$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$err, "(", objectname, ")\n")
        }
        else
        {
          # print data
          cat (objectname, ":", i$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 -8.92249e-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 0.00517335 
#> Saturn : 40.3956 -2.44482 8.6528 -0.0199448 0.00474316 
#> Uranus : 314.809 -0.658333 20.7272 0.0503435 0.000250012 
#> Neptune : 303.193 0.234991 31.0245 0.0355701 -0.000223653 
#> 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 -0.0543821 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
  1. At the end of your computations close all files and free up memory:
swe_close()