Calculate the sidereal time (in degrees).

`swe_sidtime(jd_ut)`

- jd_ut
UT Julian day number as double (day)

`swe_sidtime`

returns the sidereal time as double (deg)

- swe_sidtime()
Determine the sidereal time.

Section 15 in http://www.astro.com/swisseph/swephprg.htm. Remember that array indices start in R at 1, while in C they start at 0!

```
swe_sidtime(2451545)
#> [1] 18.69714
```