Differences

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--- en:documentation:computation_method_and_precision [2014/02/22 11:24] – [Alt/Az positions] pch
+++ en:documentation:computation_method_and_precision [2018/12/06 11:34] (current) – [Planets equatorial positions] pch
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-====== Computation method and precision ======
+====== Computational method and precision ======
 This page give some information about the computation method used by //Cartes du Ciel - Skychart// and the precision you can expect for the displayed values.
@@ Line 28: / Line 28: @@
 The position of the planets are computed using the JPL ephemeris or if no file are found for the current date, the library [[http://www.moshier.net/|plan404 by Steve Moshier]] that allows for computation from -3000 to +3000 with a precision better than one arc second.\\
-By default an extract of DE405 valid between 2000 and 2050 is supplied with the program. So the first thing to do if you want long term high precision planet position is to install a [[ftp://ssd.jpl.nasa.gov/pub/eph/planets/Linux/|full DExxx]] file.\\
+By default an extract of DE430 valid between 2000 and 2050 is supplied with the program. So the first thing to do if you want long term high precision planet position is to install a [[ftp://ssd.jpl.nasa.gov/pub/eph/planets/Linux/|full DExxx]] file.\\
 DE431 is recommended if you can afford the 2.5GB download. With this file you can compute precise planet position and nutation between -13000 and +17000.
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 Then precession, parallax and apparent position is computed the same as for the planets.
-When using current element data the precision is expected to be about 0.1 arcsec.\\
+The orbit computation use the classic two body solution, no perturbation from other body is taken into account. When using current element data the precision is expected to be about 0.1 arcsec.\\
 You can reliably compute the asteroids and comets position only for a few month around the date of the elements. So it make no sens to compute this position for a date far in the past or future.