StarPlot Documentation

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0. Guided Tour of StarPlot

The first thing to know about StarPlot is its purpose. The main goal of StarPlot is to show the spatial relationships between different star systems, not to display a realistic simulation of how they would actually look when seen in space. For that, you may want to try the much more ambitious program Celestia by Chris Laurel. Think of StarPlot as a road map and Celestia as the actual landscape. That said, you might find a guided tour of StarPlot useful to see what it can do.

0.1. Getting Started

0.1.1. For a generic UNIX-like operating system

I assume you have already installed StarPlot itself. You will need to install the Gliese and Yale sets of star data for this tour. From the StarPlot data file web page (http://starplot.org/datafiles.html), download the "Third Catalogue of Nearby Stars for StarPlot 0.95" (often called the Gliese Catalog) and the "Yale Bright Star Catalog for StarPlot 0.95."

Once you've downloaded them, open up an xterm (or other terminal) and run the commands

starpkg yale5-0.95.tar.gz ; starpkg gliese3-0.95.tar.gz

to convert the data files to StarPlot format. This will create the files "gliese3.stars" and "yale5.stars" in your current directory. (In the future, StarPlot will include a graphical dialog box from which you will be able to download and install data files automatically.) You should move these files into the directory /usr/local/share/starplot, where it will be easier to find them from StarPlot's file opening dialog. (You will probably need to log in as root to move the files there.)

0.1.2. For Debian GNU/Linux

The distributor of your operating system may also have packaged the Gliese and Yale catalogs already. If you are using Debian GNU/Linux, for instance, instead of following the above steps you can simply run

apt-get install starplot gliese yale

	apt-get install stardata-common

while logged in as root. Your /etc/apt/sources.list file will need to include the non-free section. Note that the stardata-common package is present only in the "etch", "lenny" and "sid" versions of Debian; if you have an earlier version of Debian ("sarge" or "woody"), don't run the second command above. The catalogs in StarPlot format will be automatically generated for you in the /usr/share/starplot directory. In this case they will be named gliese.stars and yale.stars (without any digits in the names).

0.1.3. For Fedora Linux

If you are using Fedora Linux (version 7 or newer), you can install StarPlot and the data packages by running

yum install starplot

	yum install starplot-gliese3 starplot-yale5 starplot-contrib

while logged in as root. The catalogs in StarPlot format will be automatically generated for you in the /usr/share/starplot directory. The files will be named gliese3.stars and yale5.stars. The file stars_with_planets3.stars from the starplot-contrib package is a set of stars known to have planets, contributed by Vince Barwinski. (Non-Fedora users may obtain this catalog from the StarPlot data files web page.)

0.2. Exploring Our Stellar Neighborhood

Go ahead and run StarPlot by entering the command

starplot &

(you may also be able to run StarPlot from a menu entry on your desktop if one exists). Then, in the StarPlot main window, select the "File->Open Star Database" menu option and choose the file gliese.stars or gliese3.stars (whichever exists on your system).

You can also save a step by telling StarPlot to open the correct file at the command line. For instance, supposing that the Gliese catalog is named gliese3.stars and is in your current directory, you would type

starplot ./gliese3.stars &

However you started StarPlot, you should now be at a screen that looks a lot like this:

The Sun is at the center of the chart, and some of the nearest stars, those within 10 light-years of us, are shown. (A light-year is the distance that a beam of light travels in one year. The distances in interstellar space are almost incomprehensibly vast!) You've probably heard of Alpha Centauri (the nearest star system) and Sirius (the star that appears brightest in our sky). The other stars are dim red dwarfs unfamiliar to most people. The color of the dots representing stars is roughly the same as their actual color in the sky: hot stars are blue and cool stars are red, while stars having a temperature similar to our Sun are shown in yellow. The relative sizes of the dots represent the stars' brightnesses.

If you want to view the star chart from a different angle, this is as simple as clicking on the four buttons in the button bar at left with arrows on them. At any point, if you find a view you like, you can save it as an image (PNG format) from the "File->Save Chart as PNG" menu option.

Let's zoom out a bit. Click the button at the upper left of the window that looks like . (It's the third button from the top.) Click it again. Each click zoomed you out by a factor of two, so the chart is now 80 light-years across, and it shows you stars within 40 light-years of the Sun. (You can verify this by checking the value displayed for "Chart Radius" under the CHART STATUS heading at the upper left of the display.) You'll note that the red dwarfs, and even the Sun, have disappeared. In fact, the only star still visible that was in the original chart is Sirius, now near the center of the display. This is because StarPlot tries not to clutter the chart with too many stars at once, so by default it doesn't show dimmer stars as you zoom out.

Your display will now look something like this. (You may be viewing the chart from a completely different angle if you played with the arrow buttons.) These are the brighter stars within 40 light-years:

What if you want to see all the dimmer stars that StarPlot isn't showing you? You can do so by clicking the button that looks like a number of times. (This button is the fifth from the top in the newest version of StarPlot, or at the bottom in StarPlot version 0.95.4 or older.) With each click, you will view stars one-half magnitude (a factor of 1.58 times) dimmer. (Magnitudes are explained in the next chapter if you aren't familiar with them.) Go ahead and keep clicking it until the label "Dim Mag:" under the CHART STATUS heading is immediately followed by the number 10. (For now, ignore the second value in parentheses, if there is one.) To make the chart less cluttered, let's also get rid of those vertical reference bars by selecting the menu option "Options->Toggle Bars". The chart now looks like this, and clicking the same button more will show you ever more dim red dwarfs if you like.

You may be interested in viewing a Hertzsprung-Russell (H-R) diagram of these stars. If you don't know what this diagram is, check out the next chapter, but basically it is a scatter plot of star brightnesses (magnitude) against star temperatures (spectral class). By convention, stars are brighter (magnitude decreases) going upward, and temperature decreases going toward the right. To view the H-R diagram, select the menu option "Stars->HR Diagram." You will get a window that looks like the one shown below. Note the gray horizontal bar near the bottom indicating the limiting dim magnitude. While this window is displayed, you can continue to make changes to the chart in the main window, and the H-R diagram will automatically stay updated to show the stars currently displayed on the chart.

Want to look at only the Sun-like stars in this region, which might conceivably harbor Earth-like planets? This isn't too difficult. Click on all the circles in the legend at the upper right of the main StarPlot window to turn off those types of stars, EXCEPT for the yellow and orange circles labeled "G" and "K". (Your legend should now appear as shown at left. If you've mistakenly clicked on the yellow or orange circle, click on it again to toggle it back on.) This selects only stars of temperature similar to the Sun.

Next, open up the "Chart->Star Filter" dialog box from the menu. In the box for "Smallest (brightest) allowed magnitude," enter "3.5", and in the box for "Largest (dimmest) allowed magnitude," enter "7.0". Then click "OK." This selects only stars of brightness similar to the Sun (whose absolute magnitude is about 4.8). Your chart will now appear something like the one shown below. Note the Sun at the center, and α (alpha) Centauri nearby.

To get information about these stars, select Options->Star Labels->Numerical Index from the menu. This will label stars with numerical indices instead of names, to save space. Now, open up the star information dialog from the menu option Stars->Chart Data. Voila—a display of information for all the Sun-like stars within 40 light-years of us! (Note that you can click on any of the column headers to sort the stars by that column.) Like the HR diagram, this window will be automatically updated any time you make changes in the main chart window.

[Information about Sun-like stars within 40 LY]

You can re-center the chart on a star other than the Sun if you like. To demonstrate this, let's first undo all our changes that made us see only Sun-like stars. Select the "Chart->Star Filter" menu option, and in the dialog box that appears, click the "Revert" button at bottom center. Also, select the menu option "Options->Toggle Bars" followed by "Options->Star Labels->Landmark Stars" to return to the original appearance of the chart. This will give you back the view seen in this image.

With the mouse, now left-click on the symbol (not the label) for the star Arcturus. You have jumped to a different position; the chart is centered on Arcturus and shows the bright stars within 40 light-years of Arcturus. If the Sun were visible, it would be near the edge of the chart.

Another entertaining thing to do is to zoom in by a ridiculous amount. Now that the chart is centered on Arcturus, keep pressing the "zoom in" button (looking like ) until its symbol begins to swell and fill most of the display. The chart radius at this point is 2.38·10^-6 light-years, or about 0.15 astronomical units (23 million kilometers). Instead of the star's brightness, the diameter of the symbol now represents the actual diameter of the star at this scale. For an interesting comparison, open the Chart->Define Chart dialog box, type "Sun" into the star name entry box and click "Search." Then hit "OK" to jump back to the Sun. You will see that the Sun is much smaller in actual size than Arcturus is. In the graphic below, for a direct comparison the Sun has been superimposed at the lower right of the chart display showing Arcturus.

0.3. Around the Galaxy

Let's now look at stellar structures on larger scales. The Gliese catalog only includes stars within about 80 light-years of Earth, so we must abandon it here. In the StarPlot main window, select the "File->Open Star Database" menu option and choose the file yale.stars or yale5.stars (whichever exists on your system). If you wanted, you could keep the Gliese catalog open as well by using the "File->Merge Star Database" menu option to select the Yale catalog instead, but that might be confusing because the two files contain some of the same stars, which would therefore be shown twice in slightly different locations.

This tour could continue to take you through StarPlot step-by-step just as above, but now that you know something about the program that would be tedious. Happily, StarPlot has the ability to save and load "parameter files" containing all the information about the current state of the program at any moment. So just copy the following parameter files, which have already been set up for you, into your home directory:

The first stop is the Hyades star cluster, the nearest star cluster to Earth. This cluster consists of a few hundred stars that formed from the same nebula, and over time have spread out over a region about 50 light-years across. Just select the menu option "File->Open Parameter File," and select the file hyades.par that you earlier copied into your home directory. The resulting view is shown below. In this case the plane of the chart is shown in blue to indicate that you are viewing it from below, to match the view of this star cluster we actually see from Earth. The brightest star in the cluster is Aldebaren, a red giant which is just left of center in this view.

Our next stop is the Scorpio-Centaurus Association, an extended group of hot blue stars. Like the Hyades, these stars formed together, but being less gravitationally bound to each other, they have spread across hundreds of light-years. They make up most of the stars that we see in the constellations of Scorpius, Centaurus, and Crux in the southern sky. Open the scocen.par parameter file using the "File->Open Parameter File" menu option to obtain the chart shown below.

Finally, we look at a large fraction of the plane of our galaxy. Open the galplane.par parameter file. What you see is a selection of the brightest stars in the galaxy, making up part of the galactic disk. The Galactic coordinate system is used in this view so that the disk is in a horizontal plane within the chart. (You can convert back to the "normal" celestial coordinate system from the Options->Coordinate System submenu.) Try clicking the button that looks like a few times to view the Galactic disk edge-on and see just how thin it is. The center of our galaxy is toward the back of the chart, although it is still well outside the volume of space shown.

This ends the tour of StarPlot. To learn more about stellar astronomy and stars themselves, turn to the next chapter. For a more thorough guide to StarPlot features, start with Chapter 2.