Frequently asked questions
Swiss Ephemeris > For Programmers
can I find more information on the Swiss Ephemeris?
You can find a full documentation under www.astro.com/swisseph/. The Swiss Ephemeris is designed for developers of astrological software. It consists of files that are not really useful until they are read by software which you have to develop first. For commercial use of Swiss Ephemeris you must purchase a license.
I compute the planetary nodes with Swiss Ephemeris?
A programmer can use our Swiss Ephemeris package to compute the planetary nodes. There are functions provided for the osculating nodes of any celestial body.
Please, see chapter 5 of the Programmer's documentation for the Swiss Ephemeris. For celestial bodies with mean theories (Mercury to Neptune) mean nodes are also available, for the others (Pluto and all 500'000 asteroids) only osculating nodes are available.
If you are not a programmer, please use the Swiss Ephemeris test page at
See Swiss Ephemeris full documentation, section 2.2.4 for more explanation.
it possible to calculate an asteroid ephemeris?
You can easily create such an ephemeris yourself on our website, and then copy-paste it to a local document on your computer.
First, go to the Extended Chart Selection and use the link provided at the very bottom of the page to find the number of this asteroid. It is 1981 for Midas, for example. To include it in any chart, just enter this number in the field on the extended chart selection page.
For a simple ephemeris, you need to use the Swiss Ephemeris test page.
Fill out the form like this (or study the explanation page to find out for yourself):
start date: whatever you like
steps -n: 365 (for a 5-year ephemeris in 5-day steps)
stepsize -s: 5
planet selection -p: s
output format -f: PTLBD
(P = planet name, T = date, L = longitude, B = latitude, D = declination)
other options: -xs1981
(-xs followed by the number of the Asteroid you wish)
If you prefer signs and degrees instead of 360-degree notation for longitude, replace L with Z.
Now click on the 'submit' button.
There are also instructions how to do it at the bottom of the Haumea ephemeris http://www.astro.com/swisseph/haumea.htm
The objects can be found at http://www.astro.com/swisseph/astlist.htm
can I find historical declination data?
For individual dates, you can run a chart and then access the additional data tables (link on top of the chart)
There, declination is also listed.
A declination ephemeris can be created in the Ephemeris section of Extended Chart Selection, and any year between 13'000 BCE and 17'000 CE can be chosen.
- How can it be found if a planet is retrograde?
You have two possibilities to determine the direction of a planet's movement:
a) you compute the ecliptic longitude for two moments, close to each other in time (like one minute later) and check whether the ecliptic longitude has increased or decreased.
It is like taking two photos of a car passing in front of your your window. If the car in the second photo is found more forward on the street, its motion is direct. If it is found more backward, its motion is retrograde.
b) you compute the position for one moment with the speed flag set. Then you look at the speed in longitude value, whether it is positive or negative. This value is found in xx.
int swe_calc_ut (double tjd_ut, int ipl, int iflag, double* xx, char* serr), where tjd_ut = Julian day, Universal Time ipl = body number iflag = an integer containing bit flags that indicate what kind of computation is wanted xx = array of 6 doubles for longitude, latitude, distance, speed in long., speed in lat., and speed in dist. serr = character string to return error messages in case of error.