Chapter 9. Questions and Answers

This document may have been updated since your installation. You can find the latest version at http://docs.kde.org/current/kdeedu/.

9.1. What is the KStars Icon?
9.2. What do the different symbols for deep-sky objects mean?
9.3. What do the different colors of Deep-sky objects mean?
9.4. Why are there so many more U.S. cities than in other countries? Is it a conspiracy?
9.5. Why can't I display the ground when using Equatorial Coordinates
9.6. Why do the faint stars and non-Messier deep sky objects disappear when I am scrolling the display?
9.7. I don't understand all the terms used in KStars. Where can I learn more about the astronomy behind the program?
9.8. How accurate/precise is KStars?
9.9. Can I help contribute to future versions of KStars?
9.1.

What is the KStars Icon?

The KStars Icon is a sextant, a handheld telescope which was used by navigators on sailing ships back when the stars were important for navigation. By carefully reckoning the positions of the stars, the navigator could get an accurate estimate of the ship's current longitude and latitude.

9.2.

What do the different symbols for deep-sky objects mean?

The symbol indicates the object type:

  • dotted circle: Open Cluster

  • cross-in-circle: Globular Cluster

  • box: Gaseous Nebula

  • diamond: Supernova Remnant

  • circle with outer lines: Planetary Nebula

  • ellipse: Galaxy

9.3.

What do the different colors of Deep-sky objects mean?

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 popup menu (the default “extras” color is red).

9.4.

Why are there so many more U.S. cities than in other countries? Is it a conspiracy?

It may be a conspiracy, but KStars is not involved! We were unable to find a single longitude/latitude database that covers the globe equitably. We are currently working on adding many more non-U.S. cities to the database. We have already received city lists from users in Norway, Italy and Korea. If you can contribute to this effort, please let us know.

9.5.

Why can't I display the ground when using Equatorial Coordinates

The short answer is, this is a temporary limitation. There is a problem when constructing the filled polygon that represents the ground when in Equatorial mode. However, it doesn't make too much sense to draw the ground in equatorial coordinates, which is why this fix has been given a low priority.

9.6.

Why do the faint stars and non-Messier deep sky objects disappear when I am scrolling the display?

When you update the display's central position, KStars must recompute the pixel 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 becomes 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 View Options window, or even customize which objects get hidden.

9.7.

I don't understand all the terms used in KStars. Where can I learn more about the astronomy behind the program?

The KStars Handbook includes the AstroInfo Project; 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: <kstars-info@lists.sourceforge.net>.

9.8.

How accurate/precise is KStars?

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 aren't a professional astronomer, you'll probably never have a problem with its accuracy or precision. There are two occasions where it may be noticeable: eclipses, and rise/set times. As discussed below, the position of the Moon is extremely hard to predict with high precision, so you probably cannot use KStars to predict eclipses at this time.

Here is a list of some of the complicating factors which limit the program's precision:

  • 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 learned in school that planets follow simple elliptical orbits around the Sun, but this isn't 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 (i.e., 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.

    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.

    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.

    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.

    The discussion of very remote dates is currently somewhat moot because the QDate class we use for storing dates does not allow dates prior to October 1752 (when the currently-standard Gregorian calendar was adopted; see the article on Leap Years). However, you can enter future dates up to around 8000 AD. We'd like to implement our own date class that allows for more remote dates in the past.

9.9.

Can I help contribute to future versions of KStars?

Yes, definitely! Introduce yourself on our mailing list: <kstars-devel@kde.org>. If you want to help with the coding, download the latest CVS version of the code and dive right in. There are several README files in the distribution that explain some of the code's subsystems. If you need ideas of what to work on, see the TODO file. You can submit patches to kstars-devel, and feel free to post any questions you have about the code there as well.

If you aren't into coding, we can still use your help with i18n, docs, AstroInfo articles, URL links, bug reports, and feature requests.