**
What is SOLEX and what does SOLEX do?**
The name comes from “**SOL**ar
system
integration by a fast
**EX**trapolation method”, and, indeed, **SOLEX**
computes the positions of solar system bodies (planets, asteroids and
comets)
by a method which is *entirely based* on the
*numerical integration*
of the Newton equation of motion.

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This means that, once the
position
and velocity of each body is known at a given starting instanct, the
acceleration
arising from the mutual gravitational forces is computed, and then the
new position and velocity after a suitably short time interval (the
stepsize)
can be predicted. The procedure can be iterated, so that the whole
orbits
are generated. A beautiful and simple description of the general idea
was
given by Feynmann in its famous Physics textbook. The more
sophisticated
integration technique actually implemented by **Solex**, as well as
the Solar System model adopted, have been described by the author (Download
reprint).
On one hand the numerical
integration
approach introduces a limitation for the user: it is *not possible*
to feed a date to the program and to get the planetary configuration in
response. If the date were to be changed, the planets would still
travel
following their original clock. Planets must instead travel from the
initial
starting epoch to the desired epoch, and the time required depends on
the
time interval between the two epochs and on the machine speed. On my
2.0 GHz Pentium M760 notebook, hundred years orbiting of the Solar
System (including
the three major asteroids Ceres, Pallas and Vesta) takes less than 5
seconds. Still, if we were interested in the Christmas night sky of
year
1 BC (astronomical year 0), starting from the present epoch (say
January
1st, 2009), one and a half minute would be needed to reach the desired
epoch. This
limitation is overcome by **Solex** by using a database of
precalculated
starting conditions, among which the program will chose the one which
is
closest in time to the target epoch. Therefore the initial “go to
epoch”
waiting time is reduced to not more than a few seconds (if the target
epoch
is within the time span covered by the library). After this affordable
cost is payed, the reward comes back: whatsoever astronomical
phenomenon
is always *dynamically reproduced*. The Solar System is "alive",
and
the moving bodies can be seen from any point of view, static or
dynamic,
according to various coordinate systems and at variable speed, forward
or backward in time. Everything combined with an *unmatched precision*,
fully comparable to that given by the Astronomical Almanac or by the
JPL "on-line" Horizon ephemerides, and generally
superior to that given by computer programs implementing analytical
methods.
Libraries containing starting condition for ca. 130000 numbered
asteroids
and ca. 600 comets are available to the program, which can then
integrate
the “expanded” solar system up to any desired epoch (at a rate of up to
35s/millennium on a Pentium 3 GHz machine). Besides the library objects
**Solex**
can easily handle custom bodies and also Earth’s satellites. Moreover,
a fictitious Solar System can easily be loaded to the program, to model
the gravitational dynamics of N-body systems and to get insights on
aspects
such chaos, perturbing effects of heavy planets, relativistic effects
of
a very massive star and so on ...
The new
**version 10** keeps the planetary libraries (matching either the
JPL DE406 or DE421 ephemerides) extended to
epochs as far as +/- 150000 years. It takes just a few
seconds to experience the virtual emotion of the simultaneous transit
of Mercury and Venus on the solar disk, which will take place on
July 26 (Dynamical Time) 69163 ! (Download
reprint)

The star library now includes stars up to magnitude 12.0 from the
NOMAD1 catalog and a number of NGC objects up to
magnitude 13.5. Aesthetically pleasant sky views can be displayed,
statically or
dynamically,
at any desired magnification and in any direction, in either
equatorial,
ecliptic or horizontal coordinate frame and from any terrestrial or
extra-terrestrial
point of view. A further feature is the ability to handle as many
body as desired all together and to run a systematic search for the
prediction of
close approaches between bodies, both in space (close encounters) and
angular
(close conjunctions, eclipses or mutual occultations, including star
occultations and multiple conjunctions).
The path of an occultation or that of a central solar eclipse on the
Earth’s
surface can also be mapped. An important feature is also that of
giving
uncertainty estimates along with the prediction of asteroidal
occultations.

For people
interested in programming, the source
code to Solex 10 is written
in
BASIC for the PowerBasic
Console Compiler 3.0. Graphic functions are implemented through the
Console Tools +
Graphics addon to the PowerBasic
compiler. Solex 10 implements the
Extended Precision arithmetics, so that the numerical integration is
done with an arithmetical precision equivalent to 19 significant
decimal digits.<>

In conclusion, **Solex 10** is a very precise ephemeris generator,
a
Planetarium, an advanced Celestial Mechanics' device and a serious
research
tool. Above all, it can be a self-instruction tool to be explored and
enjoied.