Warning, /education/kstars/doc/faq.docbook is written in an unsupported language. File is not indexed.

 <chapter id="faq">
 <title>Questions and Answers</title>
 
 <qandaset id="faqlist">
 
 <qandaentry>
 <question>
 <para>What do the different symbols for deep-sky objects mean?</para>
 </question>
 <answer>
 <para>
 The symbol indicates the object type:
 <itemizedlist>
 <listitem><para>dotted circle: Open Cluster</para></listitem>
 <listitem><para>cross-in-circle: Globular Cluster</para></listitem>
 <listitem><para>box: Gaseous Nebula</para></listitem>
 <listitem><para>diamond: Supernova Remnant</para></listitem>
 <listitem><para>circle with outer lines: Planetary Nebula</para></listitem>
 <listitem><para>ellipse: Galaxy</para></listitem>
 </itemizedlist>
 </para>
 </answer>
 </qandaentry>
 
 <qandaentry>
 <question>
 <para>What do the different colors of Deep-sky objects mean?</para>
 </question>
 <answer>
 <para>
 Generally, the different colors indicate to which catalog the object
 belongs (Messier, NGC or IC).  However, some objects have a different
 color which indicates that there are extra images available in the
 <link linkend="popup-menu">popup menu</link> (the default
 <quote>extras</quote> color is red).
 </para>
 </answer>
 </qandaentry>
 
 <qandaentry>
 <question>
 <para>
 Why are there so many more U.S. cities than in other countries?
 </para>
 </question>
 <answer>
 <para>
 When we started &kstars;, we were unable to find a longitude/latitude
 database that covered the globe equitably.  However, the &kstars;
 community is rapidly overcoming this problem!  We have already
 received city lists from many users around the world.  If you can
 contribute to this effort, please send us your list of cities and
 coordinates.
 </para>
 </answer>
 </qandaentry>
 
 <qandaentry>
 <question>
 <para>
 How can I add a new custom location to &kstars;?
 </para>
 </question>
 <answer>
 <para>
 If you would like to use a location that is not on the list, enter the
 relevant information (longitude, latitude, city name, province name, and
 country name), then press <guibutton>Add City</guibutton> button.
 All fields must be filled, except the optional province field.
 You can also modify the values for an existing city, by simply changing
 the values in the window, and adding it to the list.
 </para>
 </answer>
 </qandaentry>
 
 <qandaentry>
 <question>
 <para>
 I have added a custom location to &kstars; that I no longer want.  How
 do I remove it from the program?
 </para>
 </question>
 <answer>
 <para>
 You can easily remove a custom location from &kstars; by selecting it in the
 cities list and pressing the <guibutton>Remove City</guibutton> button.
 Note that you can not remove a &kstars; default city.
 </para>
 </answer>
 </qandaentry>
 
 <qandaentry>
 <question>
 <para>Why do some objects disappear when I am scrolling the
 display?</para>
 </question>
 <answer>
 <para>
 When the display is in motion, &kstars; must recompute the screen
 coordinates of every object in its database, which involves
 some pretty heavy trigonometry.  When scrolling the display (either
 with the arrow keys or by dragging with the mouse), the display may
 become slow and jerky, because the computer is having trouble keeping
 up.  By excluding many of the objects, the computational load is
 greatly reduced, which allows for smoother scrolling.  You can turn
 off this feature in the <guilabel>Configure - &kstars;</guilabel> window,
 and you can also configure which objects get hidden.
 </para>
 </answer>
 </qandaentry>
 
 <qandaentry>
 <question>
 <para>I do not understand all the terms used in &kstars;.  Where can I
 learn more about the astronomy behind the program?</para>
 </question>
 <answer>
 <para>
 The &kstars; Handbook includes the <link linkend="astroinfo">AstroInfo
 Project</link>; a series of short, hyperlinked articles about
 astronomical topics that can be explored and illustrated with &kstars;.
 AstroInfo is a community effort, like GNUpedia or Everything2.  If
 you'd like to contribute to AstroInfo, please join our mailing list:
 <email>kstars-devel AT kde.org</email>.
 </para>
 </answer>
 </qandaentry>
 
 <qandaentry>
 <question>
 <para>I want &kstars; to start up with a time and date different from
 my system CPU clock.  Is this possible?</para>
 </question>
 <answer>
 <para>
 Yes; to start &kstars; with a different time/date, use the
 <option>--date</option> argument, followed by a date string like
 <quote>4 July 1976 12:30:00</quote>
 </para>
 </answer>
 </qandaentry>
 
 <qandaentry>
 <question>
 <para>I want &kstars; to start up with the simulation clock paused.
 Is this possible?</para>
 </question>
 <answer>
 <para>
 Yes; to start &kstars; with the clock paused, simply add the
 <option>--paused</option> argument to the command line.
 </para>
 </answer>
 </qandaentry>
 
 <qandaentry>
 <question>
 <para>How accurate/precise is &kstars;?</para>
 </question>
 <answer>
 <para>
 &kstars; is pretty accurate, but it is not (yet) as precise as it can
 possibly be.  The problem with high-precision calculations is that
 you start having to deal with a large number of complicating factors.
 If you are not a professional astronomer, you will probably never have a
 problem with its accuracy or precision.
 </para>
 <para>
 Here is a list of some of the complicating factors which limit the
 program's precision:
 <itemizedlist>
 <listitem>
 <para>
 Planet positions are only accurate for dates within 4000 years
 or so of the current epoch.  The planet positions are predicted using
 a Fourier-like analysis of their orbits, as observed over the past few
 centuries.  We learnt in school that planets follow simple elliptical
 orbits around the Sun, but this is not strictly true.  It would be true
 only if there was only one planet in the Solar system, and if the Sun
 and the planet were both point masses.  As it is, the planets are
 constantly tugging on each other, perturbing the orbits slightly, and
 tidal effects also induce precessional wobbling.  In fact, recent
 analysis suggests that the planets' orbits may not even be stable in
 the long term (&ie;, millions or billions of years).  As a rule of
 thumb, you can expect the position of a planet to be accurate to a few
 arcseconds between the dates -2000 and 6000.
 </para><para>
 Pluto is the exception to this; its position is perhaps ten times less
 precise than the positions of the other planets.  Still, for dates
 near the present epoch, its position can be trusted to about an
 arcsecond.
 </para><para>
 The moon's position is the most difficult to predict to high precision.
 This is because its motion is quite perturbed by the Earth.  Also,
 since it is so nearby, even minute effects that would be undetectable
 in more distant bodies are easily apparent in the moon.
 </para><para>
 The objects with the worst long-term precision in the program are the
 comets and asteroids.  We use a very simplistic orbital model for the
 minor planets that does not include third-body perturbations.
 Therefore, their positions can only be trusted for dates near the
 present epoch.  Even for the present epoch, one can expect positional
 errors among the minor planets of order 10 arcseconds or more.
 </para>
 </listitem>
 </itemizedlist>
 </para>
 </answer>
 </qandaentry>
 
 <qandaentry>
 <question>
 <para>Why do I have to download an improved NGC/IC catalog and Messier
 object images?  Why not just include them as part of the &kstars; distribution?</para>
 </question>
 <answer>
 <para>
 The author of the downloadable NGC/IC catalog has released it with the restriction that it may not be used commercially.  For most &kstars; users, this is not a problem.  However, it is technically against the &kstars; license (the <acronym>GPL</acronym>) to restrict usage in this way.  We removed the Messier object images from the standard distribution for two reasons:  to simply reduce the size of &kstars;, and also because of similar licensing concerns with a couple of the images.  The inline images are significantly compressed to a very low quality from their original form, so I doubt there is a real copyright concern, but I did obtain explicit permission from the images' authors to use the few images for which there was any question about it (see <filename>README.images</filename>).  Still, just to be absolutely safe, I removed them from the standard distribution, and marked the download archive as being <quote>free for non-commercial use</quote>.
 </para>
 </answer>
 </qandaentry>
 
 <qandaentry>
 <question>
 <para>I am really enjoying the beautiful images I have downloaded through &kstars;!  I would like to share them with the world; can I publish a calendar featuring these images (or are there any usage restrictions on the images)?</para>
 </question>
 <answer>
 <para>
 It depends on the image, but many of the images restrict against commercial usage.  The Image Viewer's statusbar will usually contain information about the image's copyright holder, and what usage restrictions apply.  As a rule of thumb:  anything published by NASA is in the public domain (including all HST images).  For everything else, you can pretty safely assume that the images may not be used commercially without permission.  When in doubt, contact the image's copyright holder directly.
 </para>
 </answer>
 </qandaentry>
 
 <qandaentry>
 <question>
 <para>Can I help contribute to future versions of &kstars;?</para>
 </question>
 <answer>
 <para>
 Yes, definitely!  Introduce yourself on our mailing list:
 <email>kstars-devel AT kde.org</email>.  If you want to
 help with the coding, download the latest <ulink
 url="https://invent.kde.org/education/kstars">&kstars; &git;</ulink> version of the
 code and dive right in.  There are several <filename>README</filename> files in the
 distribution that explain some of the code's subsystems.  If you
 need ideas of what to work on, see the <filename>TODO</filename> file.  You can submit
 patches to kstars-devel mailing list, and feel free to post any questions you
 have about the code there as well.
 </para><para>
 If you are not into coding, we can still use your help with i18n, docs,
 AstroInfo articles, &URL; links, bug reports, and feature requests.
 </para>
 </answer>
 </qandaentry>
 
 </qandaset>
 </chapter>