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Celestia: The final frontier at the click of a mouse

Celestia is a 3D astronomy application developed by Chris Laurel. The program allows students to travel through the universe, modeled after the actual universe - at least what is known to mankind - at any speed, in any direction and at any time in history. Celestia displays and interacts with objects ranging in scale from artificial satellites to entire galaxies in three dimensions, from perspectives which would not be possible in a typical school planetarium or textbook photographs.

NASA has used Celestia in conjunction with trajectory analysis software and even created a web-based Celestia exploration activity for educational use.[1]

Celestia can be downloaded for Linux, Mac OS X, and MS Windows XP and Vista. Celestia is free, open-source software available through the General Public Use License (GNU).

Viewing Earth in Celestia

Basic Operations

Celestia will start up in a window, and if everything is working correctly, you'll see Earth in front of a field of stars. Displayed on-screen, is some information about your target (Earth), your speed, and the current time (Universal Time, so it'll probably be a few hours off from your computer's clock).

Right drag the mouse to orbit Earth and you might see the Moon and some familiar constellations. Left dragging the mouse changes your orientation also, but the camera rotates about its center instead of rotating around Earth. Rolling the mouse wheel will change your distance to Earth--you can move light years away, then roll the wheel in the opposite direction to get back to your starting location. If your mouse lacks a wheel, you can use the Home and End keys instead.

When running Celestia, you will usually have some object selected. Currently, it's Earth, but it could also be a star, moon, spacecraft, galaxy, or some other object. The simplest way to select an object is to click on it. Try clicking on a star to select it. The information about Earth is replaced with some details about the star. Press G (or use the Navigation menu), and you'll zoom through space toward the selected star. If you press G again, you'll approach the star even closer.

Press H to select our Sun, and then G to go back to our Sun. Right click on the sun to bring up a menu of planets and other objects in the solar system. After selecting a planet from the menu, hit G again to travel toward it. Once there, hold down the right mouse button and drag to orbit the planet.

The Tour Guide is a list of some of the more interesting objects you can visit in Celestia. Select the Tour Guide option in the Navigation menu to display the Tour Guide window. Choose a destination from the list, click the Goto button, and you're off.

Educational Advantages and Special Features

Celestia uses the Hipparcos Catalogue (HIP) which logs almost 120,000 stars. Celestia uses the VSOP87 theory of planetary orbits which is considered to be extremely accurate. Because Celestia uses this theory, it can provide a solar and lunar finder and accurately display the orbital paths of planets, moons, satellites, spacecraft, etc.

A planetarium is a big expense for a school district. Maintaining the ceiling, projector, and other fixtures are just a few of the associated expenses with operating a planetarium. Most school districts can only afford to have one planetarium, and it is most likely found at the high school or middle school. Because of this, visiting the planetarium for classes not held at that building requires taking a field trip which can take a considerable amount of otherwise productive learning time out of the day. Due to this fact, and the schedule of the planetarium's availability, visits to the planetarium may occur as little as once a year.

Celestia now makes it possible for a student to view the entire known universe, planets, stars, moons, sun, satellites, and constellations on his or her computer screen - everything a planetarium can do and a huge amount more. Celestia also enables students to view the solar system at any point in history or the future. For example, the picture to the right shows a screenshot of Celestia showing the position of the sun and condition of the earth approximately 5 billion years from now.

The death of Earth 5 billion years from now
Solar eclipse in Celestia

Another great feature of Celestia is the eclipse finder. Celestia will display all the eclipses during a period of time specified by the user, and give students the option to go to one of the eclipse dates and view what the eclipse looks like out in space. For example, the picture on the left shows a solar eclipse from the perspective of the moon with the earth ahead and the sun directly behind. Never before has such an opportunity existed for the naked eye.

The picture on the left shows what viewing a satellite looks like in Celestia. Viewing a satellite and/or navigating to a satellite is as easy as using the task bar menus to select a satellite location. This is a feature that could be utilized in conjunction with the feature to visit any point in history when studying the Hubble Space Telescope. Students would be able to observe and see the changes and upgrades done in the last 3 maintenance missions.

Satellite as seen in Celestia
Saturn with labeled moons

Color-coded labels make it easy to see what students are looking at in Celestia. For instance, planet names are blue, and moons are green. The picture on the left shows a view of Saturn and all of its moons. From that view it is difficult to see the moons apart from the surrounding stars, so the green labels help point out exactly where Saturn's moons are.

Celestia is very economical and has almost no cost associated with its use. Celestia is available for Mac OS, Windows OS, and a few builds of Linux OS making it versatile enough to fit almost any platform. It is also open-source (GNU license) so the software is free. The only cost associated with Celestia is the cost of upgrading computer video cards in the somewhat rare case that a video card cannot support Celestia. Since Celestia is free, it can be distributed to teachers for home use so they can start using it and become familiar with it, as well as begin to create lesson plans and activities surrounding Celestia.

Possible Issues Using Celestia

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Technical Issues

On 3D accelerator cards with a limited amount of memory, resizing the main Celestia window can cause textures to disappear. This occurs because so much memory is required for the frame buffer that there's not enough left for textures. There are a several workarounds: 1) Use a smaller window, 2) Make sure your display is set to 16-bit (high color) mode, 3) Try running Celestia in full screen mode.

Celestia struggles to function normally in 256 color mode. It is best to change the color settings to 16-bit or 32-bit if those settings are supported. This may not be available on older machines.

If objects look good at a distance but get too dark when you approach them closely, try upgrading to the most current version of drivers available for the computer's video card. For some older cards, this still won't fix the problem.

For all of these technical issues, the developers are aware and are working to eliminate many of these issues in future releases of Celestia.

Education Challenges

Celestia gives the student an incredible amount of freedom to explore the entire known universe by clicking on objects and using the "Goto" key to get there or traveling freehand at any speed. It is very easy to get lost and turn around a not see the solar system behind you. Teachers need to have a good working knowledge of the program in order to support these issues if a student should become lost in the universe. The program makes it fairly easy to navigate back to the sun (press H) or any other object in space by using the task bar menus as long as the student knows how to take advantage of that feature.

Since Celestia is a 3D program, it demands a decent degree of performance from a computer's processor and video card. This could potentially be a problem for schools working with older machines - this is especially a concern for elementary schools in many cases. Generally however, Celestia can render images very quickly - much faster than the 3D environment found in Second Life for example.

There are so many activities that can be done using Celestia, teachers should have activities planned for students to do so as not to overwhelm them with the phenomenal amount of information available in Celestia.

References

  1. ^  http://learn.arc.nasa.gov/planets/ "NASA Celestia Exploration Activity"
  2. http://en.wikipedia.org/wiki/Celestia
  3. http://www.shatters.net/celestia/ Celestia Web Site

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