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tdeedu/kstars/README.ephemerides

2.9 KiB

KStars keeps track of thousands of comets and asteroids.  
It uses orbital data published by NASA's Jet Propulsion
Laboratory (JPL); these data are known as "orbital elements".
Because these small bodies are easily perturbed as they
wander about the solar system, their orbital elements must
be updated regularly. Updating the elements will also add
any recently-discovered bodies.


How to update the orbital elements of comets and asteroids:

-=( 1 )=- The Easy Way.

Start KStars, then open the "Get New Stuff" Tool by selecting
"Download Data..." from the File menu, or by pressing Ctrl+D.

If a new "ephemerides" package is available, select it and press
the Install button. Voila!


-=( 2 )=- Doing it Manually.

It is possible that the ephemerides package is not completely
up-to-date. Fortunately, it's relatively simple to update the
files manually whenever you want.

::NOTE:: If you find that the ephemerides package is woefully
outdated, and you follow this manual-install procedure, PLEASE
send your final comets.dat and asteroids.dat files to
kstars-devel@kde.org! Now is your chance to be a KStars Hero!


Step 1: The JPL Webpage

Point your browser to the following URL:
http://ssd.jpl.nasa.gov/sb_elem.html


Step 2: The Comets

Under "ASCII Files", click on the "Comets" link, and save
this file as ~/.trinity/share/apps/kstars/comets.dat (or as
$TDEDIR/share/apps/kstars/comets.dat for a system-wide install).


Step 3: The Asteroids

Under "ASCII Files", click on the "Numbered Asteroids" link,
and save this file in a working directory as "asteroids.full.dat".

This file contains about 100,000 asteroids, far more than we
want to deal with in KStars. I ship KStars with 2000 asteroids;
you may feel free to keep as many as you want (but be aware that
larger numbers will require more RAM and will use the CPU more).

So, how do we pick which of the 100,000 asteroids to keep? I
think the most sensible option is to sort the list from biggest
to smallest, and then just keep the 2000 largest (or however
many you are keeping). However, there isn't a "size" column to
sort by! Ah, but there *is* an "absolute magnitude" column
(column 10). Absolute magnitude is a measure of the asteroid's
intrinsic brightness, which is a good indicator of its size.
Smaller numbers are brighter, so sorting the file such that the
magnitudes increase means that the biggest asteroids are at the
top of the list.

Use the "sort" command to sort, and the "head" command to cut
out the first 2000 lines, like this:

% sort -n -k 10 asteroids.full.dat | head -n 2000 > asteroids.dat

[[ WARNING: There is (at least) one asteroid with spaces in its
name ("van de Hulst"), which messes up the columns for that object.
You may want to rename this object before sorting.]]

Finally, copy "asteroids.dat" to ~/.trinity/share/apps/kstars/ (for
single-user install) or $TDEDIR/share/apps/kstars/ (for system
install).