June 7, 2005

Open source software looks skyward

Author: Lee Spain

The open source software movement is making the leap from the desktop to the stars with applications like Virtual Moon Atlas, Stellarium, and Celestia. Amateur astronomers use these programs to identify lunar features, chart celestial bodies for observing sessions, and take users on virtual tours of the universe.

Virtual Moon Atlas

Since my old 60-millimeter telescope is a tad small for observing deep space objects like galaxies, my journey started with one small step to the moon. Created by a programmer (Christian LeGrand) and a lunar observer (Patrick Chevalley), Virtual Moon Atlas 2.1 is a Windows application distributed under the GNU General Public License. Written in Delphi 6, it comes in lightweight form, without OpenGL graphics, and heavyweight (basic and expert), with OpenGL graphics. The lightweight form provides a two-dimensional map of the moon and a complete database of lunar topographical features. The heavyweight form provides the same features with more graphic detail. The interfaces are identical. As a user, I simply looked at a large map of the moon on the left side of the screen, clicked on an item of interest, and read information about the feature in tabbed folders on the right side of the screen.

Each time I selected a lunar feature, Virtual Moon Atlas quickly responded with abundant information: feature type, when it was formed, dimensions, coordinates, description, level of astronomer interest, best times for observation, minimal equipment required, print references, and Web links for additional imagery. Other tabs on the right side of the screen allowed me to log my own observation notes, compute details about the position and phase of the moon, and sort the database of lunar objects based on a variety of criteria. Virtual Moon Atlas allowed me to plan several lunar observing sessions and made them more rewarding by directing me to the most intriguing objects.


My journey continued on to the planets with an exciting planetarium program called Stellarium. This beta version is available for the Linux, Windows, and Mac OS X operating systems, and requires a graphics card capable of rendering OpenGL graphics.

Stellarium took me from a light-polluted backyard and put me in a virtual country meadow for my observing session. To set up for an accurate depiction of the sky, you enter the latitude and longitude of your observing location (or guess by placing yourself on a world map), put in the date and the time of your observing session, and select how quickly you want time to move. As day gives way to night, the sky will darken and the virtual heavens reveal themselves. You can click on various celestial objects with the mouse to find out what they are, and center them in the screen by tapping the tool bar. The interface is unobtrusive and uses hotkeys extensively.

The fun really begins when you zoom in on an object. I found Jupiter, zoomed close in on it, and saw its moons. I was astonished to see that the great red spot and storms in the gaseous bands of the planet were animated! As my observing session progressed, the storms and red spot moved across the planet's face while the moons slowly made progress in their orbits. This detail far surpasses anything that I see with my puny telescope. However, Stellarium users wanting even more amazing views can find a link on the program's Web site to a company that can provide a compatible planetarium projector and planetarium dome for around $20,000.

This version 0.6.2 software generally ran smoothly, but it crashed when I tried to use its screen capture capabilities. This program closely mimicked my night sky, but I would have liked a function to create printer-friendly sky charts for my observing sessions.


For the final leg of my journey, I had to leave this planet -- the views from here can be so limiting. Fortunately, Celestia 1.3.2, an open-source application for Linux, Windows, and Mac OS X, could take me virtually to the celestial bodies.

Jupiter's moon Thebe, in Celestia - click to enlarge

I started out from a perspective in orbit high above our planet, then took a guided tour of the universe. I took command and selected the objects I wanted to visit. The application uses vast amounts of photographic imagery compiled by space agencies and astronomers worldwide to create a richly textured virtual universe. It allows users to visit celestial bodies, fly around them, and zoom in for a closer look. Celestia draws on a database of over 100,000 stars, and has a catalog of more than 100 objects in the solar system, including man-made ones. I took a look at the International Space Station, but tinkerers can add their own spacecraft.

The only drawback I found with this program was the interface. While it is clean and uncluttered, Celestia does rely heavily on mouse gestures that take some time to become familiar.

Applications like this are almost enough to make a casual observer like me leave telescopes behind. But, then again, I could take a giant leap in telescope quality for the cost of Microsoft Office, which, thanks to open source software, I no longer need to pay.

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