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Stargazing with Stellarium HOME PLANETARIUM

If you like astronomy but you don’t like sitting outside on cold nights, try stargazing from a virtual planetarium.

BY KRISTIAN KISSLING

tellarium [1] is a virtual planetar- If this is the first time you have used the libsdl-mixer1.2-dev, libsdl-gfx1.2-dev, or ium application that simulates CVS, just repeat these steps if an error libsdl1.2-sound-dev, as well as packages Sthe night sky and shows you con- message appears. CVS needs a .cvs for OpenGL, such as xlibmesa-gl-dev, stellations and celestial bodies. The goal folder in your home directory, but in- and a couple of other packages, such as of Stellarium is to provide users with a stead of just setting up the folder, it just zlib1g-dev and libpng12-dev. The CVS clear, annotated view of what they acts surprised if the folder isn’t there. version may be up to date, but it is often would see in the night sky with eyes, Now change to an empty directory and buggy. If this is the case, you can down- binoculars, or a small telescope. Like a start to download: load and build the stable version, stellar- real planetarium, the Stellarium virtual ium-0.7.1.tar.gz, off the Web [2]. Note planetarium can display a view of the cvs -z3 -d:pserver:U that some of the features described in sky from other locations on the Earth or anonymous@cvs.sourceforge.net:U this article are missing in the stable other points in history. /cvsroot/stellarium co U version. stellarium Setting Up Getting Started To use Stellarium’s full feature scope, In the new stellarium subdirectory, run Open a console window and type stellar- you will need to download the latest ver- the ./autogen.sh command to create the ium. The program comes up with a pic- sion of the program from the CVS. The configure file, and then follow the nor- turesque scene and the sky above it (Fig- cvs program, which you can install using mal steps to build and install Stellarium: ure 1). Depending on the time of day, YaST or Apt-get, is required for this. An- ./configure, make and make install with you may be able to see the stars. The other essential requirement is 3D drivers root privileges. Stellarium needs a few view depends on the program launch for your graphics adapter, as the pro- developer packages. Suse Linux requires time – Stellarium synchronizes with gram needs a fair amount of graphics the SDL-devel and xorg-x11-Mesa-devel your computer’s internal clock. There is performance. First log in to the Stellar- packages. The latter can be an issue: a status bar with a variety of information ium CVS at the command line, and press if you used YaST to install the Nvidia at the top of the screen. The current date [Enter] when you are prompted for a driver, xorg-x11-Mesa-devel will destroy and time are shown on the left, followed password: the required kernel module. by the name and program version. On You need to reinstall Nvidia, prefera- the far right, there are two values that cvs -d:pserver:U bly following the steps described on the need some explaining: fov is short for [email protected]:U Nvidia page. “Debian Etch” users need “Field of view”; you can extend or re- /cvsroot/stellarium login the SDL packages, libsdl1.2-dev, strict the field of view by pressing [PgUp]

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Figure 1: Stellarium comes up with a nature scene and lots of sky. If you launch the program after dark, you can see the stars.

through a fish-eye or a telescope. Save as and this makes sense if you zoom into default lets you store these settings. The space. Cardinal Points lets you display Rendering tab lets you specify the level letters for north, south, east, and west of detail in Stellarium, and this is where in the sky. and [PgDn]. 100 degrees gives you a fish- you enable and disable options, al- The most impressive thing about Stel- eye view; you can restrict the field of though most features can be modified larium is that it gives you command over view to a minimum of 0.001, which is via the icons on the lower left. Star time – just like the Celestia planetarium. what happens when you zoom into a re- Names, Up to mag means that the names You can go back to any point in history – mote planet. Gamers will probably have are displayed up to a certain luminosity, to view the night sky in the year 0, for guessed that FPS means “Frames per second.” If this value is too low, the dis- play will be jerky. On the lower left, you can see the vari- ous options that Stellarium offers in the form of a row of switches that you can enable or disable. The four icons on the lower right let you manipulate the time. Stellarium normally comes up in full- screen mode; pressing [F1] gives you a normal window. You can control the pro- gram by pressing keyboard shortcuts. There is a list of shortcuts on the Web at [3], or you can click the question mark icon to display the internal list. If the graphics performance is not good enough when you press the left mouse button to take a look around, you will need to tweak the video settings. To do so, click the screwdriver icon to go to the menu with the basic settings. Change to the Video tab, and reduce the Screen Resolution. The two options below Projection distort the viewer’s per- Figure 2: Planetarium in the snow. You can watch the skies from a variety of landscapes and spective; you then see your environment at different times of year.

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ward and back fields from the left relate to constella- through time, and tions. You can click on the leftmost icon the triangle in the to draw lines between groups of stars center takes you to give you a clearer view of the con- back to realtime stellation. The next box gives you the mode. In the Loca- names of the constellations. And when tion tab, you can you click the third box, artist’s impres- define the location sions show less imaginative users why of the planetar- these constellations are known by their ium. In the CVS mythical names (Figure 3). The next version, you can two icons let you drop coordinate sys- even use the tems over the imaginary celestial mouse wheel, or sphere, an Azimuthal Grid and an press [PgUp] and Equatorial Grid, both of which are coor- [PgDn] to zoom dinate systems for defining the position into the map and of a celestial body (see the Coordinate Figure 3: An artist’s impression of the constellation Capricornus. specify the loca- Systems box). tion. If you like the idea of floating silently example, or to watch future eclipses. You As an alternative, just discover the co- through space, you can just switch off can define the Current Time in Date & ordinates of your current location and the landscape and the atmosphere by Time. Below this there is a display that enter them. Wikipedia might help you clicking the next button, and the one indicates how fast time is elapsing: the track down the correct coordinates for two places to the right. The compass number 1.0 indicates realtime mode. You your location. icon between these two lets you enable can accelerate and slow down the pace This just leaves the Landscapes tab, the Cardinal Points; the button to the of time by pressing [L] or [J], and [K] which lets you change the landscapes right adds nebulae to the galaxy. Astro- takes you back to realtime. displayed by the program. Your options nomic nebulae (interstellar clouds of The icons at the bottom right give you are green meadows, forests, or a snow- dust and gas that either emit or reflect a graphical approach to changing the capped mountain – all of them are quite light) first appear as flashing yellow dots time. The double triangles take you for- breathtaking (Figure 2). in space and reveal interesting forms when you zoom in. Table 1: Stellarium Controlling the Show When you left click a specific object, Keyboard Shortcuts Time to test the small icons in the lower the celestial body is surrounded by a left corner of the screen. The first three flashing cursor: clicking on the arrow Shortcut Effect [F1] Full screen [Up-Arrow] Rotate up Coordinate Systems [Down-Arrow] Rotate down Viewed from the earth, planets rotate altitude line crosses the horizon (an arc) [Right-Arrow] Rotate right about a fixed point known as the celes- is referred to as the azimuth (Figure 4). [Left-Arrow] Rotate left tial pole. The celestial pole actually com- This coordinate system is fairly simple, Left click Select object prises two poles. If you are at the North and it is not suitable for determining the [Space] Focus on object Pole, the celestial pole is located directly exact position of an object such as a [PgUp] Zoom in on object at the zenith. The same thing applies to planet that is highly dependent on the [PgDn] Zoom out from object the South Pole, but in this case, the ze- position of the viewer and the motion of nith is known as the nadir. In other the Earth. [T] Track object words, the celestial poles are south and [Ctrl]+[S] Grab screenshot Equatorial Grid (Right Ascension/ Decli- north viewed from the equator. The [Ctrl]+[R] Record actions as script nation (RA/ Dec) coordinate system) This imaginary celestial sphere connects [7] Stop script coordinate system also uses the Hippar- these two poles, thus creating a celestial [M] Open text menu cos Star Catalog. Starting at the celestial coordinate system. The celestial equator [1] Open configuration equator, it measures the exact position resides in a plane that is at right angles menu of a star in the coordinate system. Start- to the celestial poles – just like the Earth’s ing at the vernal equinox point, a fixed equator – but the celestial poles are not star, the first angle, or right ascension, is Catalogs identical to the North and South Poles. determined along the celestial equator, Hipparcos Catalog: Based on data for Azimuthal Grid (Altitude/ Azimuth coordi- and the second angle, or declination, is the locations and movements of 118,000 nate system) A positioning method for determined by reference to the north stars collected by the Hipparcos satel- celestial bodies. Locate a fixed star and pole to pinpoint the position of a celes- lite. imagine an angle that points straight tial body in the coordinate system (Fig- down from the star to the horizon from ure 5). The RA/Dec coordinate system Messier Catalog: Lists astronomic the viewer’s perspective. This angle de- has the advantage of allowing exact po- objects, mainly galaxies, nebulae and termines the altitude. The horizontal dis- sitioning, as the celestial equator is star clusters; named for its editor tance from north to the point where the static. Charles Messier.

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Figure 4: Sketch by Andras Mohari, Matthew Gates, and the Open Figure 5: The “Right Ascension/ Declination” coordinate system is Clipart Library describing the “Altitude/ Azimuth” coordinate sys- more complex, but it is independent of the viewer’s degree of lati- tem. tude. icon focuses on the selected plant. [init_location] when your script appears. Press [M] [PgUp] and [PgDn] then let you zoom in name = Munich to quit the menu; this automatically or out. latitude = +48 08'24.00\" launches the script. You can then press longitude = +11 34'30.00\" [7] to stop the script. Moonstruck altitude = 0 [Ctrl]+[S] grabs a screenshot, which Let’s take a closer look at the moon. To the program stores below your home di- get a better view of the moon, select the The longitude and latitude values follow rectory. With the right software, you can magnifying glass icon, or press [Ctrl] the name, however, the altitude you even create your own panorama photo +[F], then open the Planets & Moons enter does not make any difference. If of a garden or park to use as a landscape tab, and enter Moon in the text box. you set the flag_show_script_bar option for your private planetarium [5]. ■ When you press [Enter] to confirm, to true, an additional input box appears Stellarium searches for and focuses on in the lower menu, allowing you to con- INFO the planet. You can then use the zoom trol Stellarium by entering various com- [1] Stellarium project homepage: functions for a close-up view of the mands. There is a command reference http:// stellarium. sourceforge. net moon, or follow its orbit by pressing [T] on the web at [4]. [2] Stellarium source code: and speeding up the pace of time. This Stellarium also supports scripting. You http:// prdownloads. sourceforge. net/ technique also works for constellations, can press [Ctrl]+[R] to record your ac- stellarium/ stellarium-0. 7. 1. tar. nebulae, or stars, which you can also lo- tions in Stellarium. The program stores gz?download cate via the search function. You can ac- the recorded actions in a file titled stel- [3] Keyboard shortcuts in Stellarium: cess stars by entering their names or larium0.sts below your home directory. http:// porpoisehead. net/ mysw/ their Hipparcos Catalog number. Nebu- Pressing [Ctrl]+[R] stops the recording. stellarium_user_guide_html/ node20. lae are located based on the Messier Launching a script is a fairly convo- html Catalog conventions. (See the box la- luted process: first, copy the stellarium0. [4] Command reference: beled "Catalogs.") sts file to the /usr/local/stellarium/data/ http:// cvs. sourceforge. net/ viewcvs. py/ scripts/startup.sts directory, then re- *checkout*/ stellarium/ stellarium/ doc/ Invisible Worlds launch Stellarium, and press [M] to go to commands. html?rev=1. 16 Stellarium has a few tricks up its sleeve; the text menu. [5] “Panoramas with Hugin, you need a /.stellarium/config.ini file in Repeatedly press [Down-Arrow] to go Enblend and Autopano-SIFT,” your home directory to use them. to item 6. Scripts, and then press by Oliver Frommel; Linux Magazine Thanks to this file, the planetarium is [Right-Arrow] to move to 6.1 Local February, 2005, pg. 48. located in Paris by default, but you can Scripts: Select and exit to run. [6] Creating your own landscape: replace this with the value for your fa- You can then browse the existing http:// porpoisehead. net/ mysw/ vorite town. The entry for the German scripts by pressing [Up-Arrow] and stellarium_user_guide_html/ node39. city Munich is as follows: [Down-Arrow] and pressing [Enter] html

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