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0001 <chapter id="faq">
0002 <title>Questions and Answers</title>
0004 <qandaset id="faqlist">
0006 <qandaentry>
0007 <question>
0008 <para>What do the different symbols for deep-sky objects mean?</para>
0009 </question>
0010 <answer>
0011 <para>
0012 The symbol indicates the object type:
0013 <itemizedlist>
0014 <listitem><para>dotted circle: Open Cluster</para></listitem>
0015 <listitem><para>cross-in-circle: Globular Cluster</para></listitem>
0016 <listitem><para>box: Gaseous Nebula</para></listitem>
0017 <listitem><para>diamond: Supernova Remnant</para></listitem>
0018 <listitem><para>circle with outer lines: Planetary Nebula</para></listitem>
0019 <listitem><para>ellipse: Galaxy</para></listitem>
0020 </itemizedlist>
0021 </para>
0022 </answer>
0023 </qandaentry>
0025 <qandaentry>
0026 <question>
0027 <para>What do the different colors of Deep-sky objects mean?</para>
0028 </question>
0029 <answer>
0030 <para>
0031 Generally, the different colors indicate to which catalog the object
0032 belongs (Messier, NGC or IC).  However, some objects have a different
0033 color which indicates that there are extra images available in the
0034 <link linkend="popup-menu">popup menu</link> (the default
0035 <quote>extras</quote> color is red).
0036 </para>
0037 </answer>
0038 </qandaentry>
0040 <qandaentry>
0041 <question>
0042 <para>
0043 Why are there so many more U.S. cities than in other countries?
0044 </para>
0045 </question>
0046 <answer>
0047 <para>
0048 When we started &kstars;, we were unable to find a longitude/latitude
0049 database that covered the globe equitably.  However, the &kstars;
0050 community is rapidly overcoming this problem!  We have already
0051 received city lists from many users around the world.  If you can
0052 contribute to this effort, please send us your list of cities and
0053 coordinates.
0054 </para>
0055 </answer>
0056 </qandaentry>
0058 <qandaentry>
0059 <question>
0060 <para>
0061 How can I add a new custom location to &kstars;?
0062 </para>
0063 </question>
0064 <answer>
0065 <para>
0066 If you would like to use a location that is not on the list, enter the
0067 relevant information (longitude, latitude, city name, province name, and
0068 country name), then press <guibutton>Add City</guibutton> button.
0069 All fields must be filled, except the optional province field.
0070 You can also modify the values for an existing city, by simply changing
0071 the values in the window, and adding it to the list.
0072 </para>
0073 </answer>
0074 </qandaentry>
0076 <qandaentry>
0077 <question>
0078 <para>
0079 I have added a custom location to &kstars; that I no longer want.  How
0080 do I remove it from the program?
0081 </para>
0082 </question>
0083 <answer>
0084 <para>
0085 You can easily remove a custom location from &kstars; by selecting it in the
0086 cities list and pressing the <guibutton>Remove City</guibutton> button.
0087 Note that you can not remove a &kstars; default city.
0088 </para>
0089 </answer>
0090 </qandaentry>
0092 <qandaentry>
0093 <question>
0094 <para>Why do some objects disappear when I am scrolling the
0095 display?</para>
0096 </question>
0097 <answer>
0098 <para>
0099 When the display is in motion, &kstars; must recompute the screen
0100 coordinates of every object in its database, which involves
0101 some pretty heavy trigonometry.  When scrolling the display (either
0102 with the arrow keys or by dragging with the mouse), the display may
0103 become slow and jerky, because the computer is having trouble keeping
0104 up.  By excluding many of the objects, the computational load is
0105 greatly reduced, which allows for smoother scrolling.  You can turn
0106 off this feature in the <guilabel>Configure - &kstars;</guilabel> window,
0107 and you can also configure which objects get hidden.
0108 </para>
0109 </answer>
0110 </qandaentry>
0112 <qandaentry>
0113 <question>
0114 <para>I do not understand all the terms used in &kstars;.  Where can I
0115 learn more about the astronomy behind the program?</para>
0116 </question>
0117 <answer>
0118 <para>
0119 The &kstars; Handbook includes the <link linkend="astroinfo">AstroInfo
0120 Project</link>; a series of short, hyperlinked articles about
0121 astronomical topics that can be explored and illustrated with &kstars;.
0122 AstroInfo is a community effort, like GNUpedia or Everything2.  If
0123 you'd like to contribute to AstroInfo, please join our mailing list:
0124 <email>kstars-devel AT kde.org</email>.
0125 </para>
0126 </answer>
0127 </qandaentry>
0129 <qandaentry>
0130 <question>
0131 <para>I want &kstars; to start up with a time and date different from
0132 my system CPU clock.  Is this possible?</para>
0133 </question>
0134 <answer>
0135 <para>
0136 Yes; to start &kstars; with a different time/date, use the
0137 <option>--date</option> argument, followed by a date string like
0138 <quote>4 July 1976 12:30:00</quote>
0139 </para>
0140 </answer>
0141 </qandaentry>
0143 <qandaentry>
0144 <question>
0145 <para>I want &kstars; to start up with the simulation clock paused.
0146 Is this possible?</para>
0147 </question>
0148 <answer>
0149 <para>
0150 Yes; to start &kstars; with the clock paused, simply add the
0151 <option>--paused</option> argument to the command line.
0152 </para>
0153 </answer>
0154 </qandaentry>
0156 <qandaentry>
0157 <question>
0158 <para>How accurate/precise is &kstars;?</para>
0159 </question>
0160 <answer>
0161 <para>
0162 &kstars; is pretty accurate, but it is not (yet) as precise as it can
0163 possibly be.  The problem with high-precision calculations is that
0164 you start having to deal with a large number of complicating factors.
0165 If you are not a professional astronomer, you will probably never have a
0166 problem with its accuracy or precision.
0167 </para>
0168 <para>
0169 Here is a list of some of the complicating factors which limit the
0170 program's precision:
0171 <itemizedlist>
0172 <listitem>
0173 <para>
0174 Planet positions are only accurate for dates within 4000 years
0175 or so of the current epoch.  The planet positions are predicted using
0176 a Fourier-like analysis of their orbits, as observed over the past few
0177 centuries.  We learnt in school that planets follow simple elliptical
0178 orbits around the Sun, but this is not strictly true.  It would be true
0179 only if there was only one planet in the Solar system, and if the Sun
0180 and the planet were both point masses.  As it is, the planets are
0181 constantly tugging on each other, perturbing the orbits slightly, and
0182 tidal effects also induce precessional wobbling.  In fact, recent
0183 analysis suggests that the planets' orbits may not even be stable in
0184 the long term (&ie;, millions or billions of years).  As a rule of
0185 thumb, you can expect the position of a planet to be accurate to a few
0186 arcseconds between the dates -2000 and 6000.
0187 </para><para>
0188 Pluto is the exception to this; its position is perhaps ten times less
0189 precise than the positions of the other planets.  Still, for dates
0190 near the present epoch, its position can be trusted to about an
0191 arcsecond.
0192 </para><para>
0193 The moon's position is the most difficult to predict to high precision.
0194 This is because its motion is quite perturbed by the Earth.  Also,
0195 since it is so nearby, even minute effects that would be undetectable
0196 in more distant bodies are easily apparent in the moon.
0197 </para><para>
0198 The objects with the worst long-term precision in the program are the
0199 comets and asteroids.  We use a very simplistic orbital model for the
0200 minor planets that does not include third-body perturbations.
0201 Therefore, their positions can only be trusted for dates near the
0202 present epoch.  Even for the present epoch, one can expect positional
0203 errors among the minor planets of order 10 arcseconds or more.
0204 </para>
0205 </listitem>
0206 </itemizedlist>
0207 </para>
0208 </answer>
0209 </qandaentry>
0211 <qandaentry>
0212 <question>
0213 <para>Why do I have to download an improved NGC/IC catalog and Messier
0214 object images?  Why not just include them as part of the &kstars; distribution?</para>
0215 </question>
0216 <answer>
0217 <para>
0218 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>.
0219 </para>
0220 </answer>
0221 </qandaentry>
0223 <qandaentry>
0224 <question>
0225 <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>
0226 </question>
0227 <answer>
0228 <para>
0229 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.
0230 </para>
0231 </answer>
0232 </qandaentry>
0234 <qandaentry>
0235 <question>
0236 <para>Can I help contribute to future versions of &kstars;?</para>
0237 </question>
0238 <answer>
0239 <para>
0240 Yes, definitely!  Introduce yourself on our mailing list:
0241 <email>kstars-devel AT kde.org</email>.  If you want to
0242 help with the coding, download the latest <ulink
0243 url="https://invent.kde.org/education/kstars">&kstars; &git;</ulink> version of the
0244 code and dive right in.  There are several <filename>README</filename> files in the
0245 distribution that explain some of the code's subsystems.  If you
0246 need ideas of what to work on, see the <filename>TODO</filename> file.  You can submit
0247 patches to kstars-devel mailing list, and feel free to post any questions you
0248 have about the code there as well.
0249 </para><para>
0250 If you are not into coding, we can still use your help with i18n, docs,
0251 AstroInfo articles, &URL; links, bug reports, and feature requests.
0252 </para>
0253 </answer>
0254 </qandaentry>
0256 </qandaset>
0257 </chapter>