Education
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Celestia |
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Celestia |
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There are several programs that display the wealth of images and data accumulated by satellites and telescopes during the past 10-20 years:
You dream of being an astronaut/cosmonaut, but struggle just to get out of bed in the morning? Now is your chance!
Celestia is a free real-time space simulation that lets you experience our universe in three dimensions. Unlike most planetarium software, Celestia doesn't confine you to the surface of the Earth. You can travel throughout the solar system, to any of over 100,000 stars, or even beyond the galaxy. All travel in Celestia is seamless; the exponential zoom feature lets you explore space across a huge range of scales, from galaxy clusters down to spacecraft only a few meters across. A 'point-and-goto' interface makes it simple to navigate through the universe to the object you want to visit. Most of the planet textures are based on image data from various NASA/JPL spacecraft.
Problems? Celestia makes use of the 3D-capabilities of your graphics card. If you find that the program is hopelessly slow, try again with a different computer and/or graphics card.
The simplest way to enjoy Celestia is to use a pre-prepared script. A celestia script will give you a tour of the solar system, or a view of Venus passing before the sun. It is not especially difficult to write your own scripts---see the additional information at the end of this page---but most people will find it more convenient to download one of the many scripts written by other users of celestia.
With a little practice, you can learn to manipulate celestia interactively. Usually this involves some interplay between the mouse and the keyboard or the menus. It will help initially to check the menu items
Options -> Objects -> Show Orbitsto help you find the otherwise small bodies hidden in space. If you start celestia interactively (not with a script), the first image will be that of Io, one of the moons of Jupiter. If the name Io is not written in the upper left corner of your screen, you need to first travel to Io. Choose from the menu Navigation -> Celestial Browser and then from the pop-up menu Sol -> Jupiter -> Io. Now click with the right mouse button on Io, and choose Goto. If you have already arrived at Io, read on.
| Mouse Commands | |
| Left click | Select a target, double click to center |
| Right click | Open a target menu, including information |
| Mouse wheel | Adjust distance to target |
| Left drag | Rotate the camera |
| Right drag | Rotate about the target |
It is quite likely that you will arrive on the dark side of Io, where the screen will be black. As a first exercise in the interactive use of celestia, hold down the right mouse button and keep dragging until you find the side of Io that is illuminated. If you are very close to Io, you must rotate the mouse wheel (or hold down both mouse buttons simultaneously and drag), to adjust your distance to Io so that the illuminated side of the moon is completely visible on the screen. At this stage the name Io will appear in the upper left of your screen, and the altitude above Io should be greater than or equal to 2000 km.
Next try to find Jupiter. Jupiter should be visible nearby, if you again hold down the right mouse button and drag, thereby rotating about the center of Io. When you find Jupiter, select it with the left mouse button, and move it to the center of the screen by double-clicking. Now click on Jupiter with the right mouse button and a menu will appear. Selecting Info from the menu will give you information on Jupiter. Selecting Satellites will list the bodies surrrounding Jupiter, including its moons. Selecting Goto will bring you much closer. Again you will have to rotate the mouse wheel to adjust your distance to the great planet so that it is completely visible on the screen. Now Jupiter should be written in the upper left of your screen, and the altitude should be at least 80,000 km.
Although it is possible to move about using the point and click method just described, the universe is large, and it is not always so easy to find things in this way. It is therefore wise to learn how to navigate using the keyboard and/or the menus.
| Action | Keyboard | Menu |
| Select a target | Enter | Navigation -> Celestial Browser (right click on the pop-up menu item) |
| Center the target | C | Navigation -> Celestial Browser (right click on the pop-up menu item) |
| Go to the target | G | Navigation -> Celestial Browser (right click on the pop-up menu item) |
| Move towards the target | Home | No menu item - Use the mouse wheel or Hold down both mouse buttons and drag |
| Move away from the target | End | |
| Zoom In | , | View -> Zoom In |
| Zoom Out | . | View -> Zoom Out |
As an example, press Enter on the keyboard, and type Saturn, followed by Enter again. You then type the letter G and you will go to Saturn. Using the menus, this operation is slightly more complicated: Navigation -> Celestial Browser followed by a pop-up menu with Sol -> Saturn. Right-clicking on Saturn and choosing Goto takes you to Saturn. The advantage of using the celestial browser is that it contains a complete list of destinations, including many which you probably never heard of. You can visit all the planets and many many stars in this way.
The difference between Move Towards and Zoom In is the same as in photography: Move Towards implies that you actually get closer to the target, while Zoom In implies that you remain in place but use the telephoto property to make a distant object fill the screen, narrowing the field of view. This distinction implies that there are two different ways to view the target: 1) GoTo the target with G, or 2) Center the target with C, followed by Zoom In.
| Action | Keyboard | Mouse |
| Follow the target | F | Right click on the target, choose Follow from the pop-up menu item |
| Sync to the target | Y | Right click on the target, choose Sync from the pop-up menu item |
Not only are celestial bodies constantly in motion with respect to each other, they also rotate. The commands Sync and Follow are designed to help you keep up! The best way to understand this is with an example. GoTo Earth, and use the Time menu to speed time up to a factor of 1000x its usual value. If the keyword Follow does not appear in the lower right corner of the screen, type F or right click on the Earth and choose Follow from the menu. You will observe that the Earth rotates against a fixed background. The point of observation can be adjusted with the menu item Navigation -> Goto Long/Lat, by selecting a latitude and longitude.
Now type Y or right click on the Earth and choose Sync from the menu.
Finally we consider a more sophisticated interactive use of the program, the passage of Venus before the sun on 8 June, 2004. On that day, Venus was visible from earth as a small shadow on the face of the sun. It could be seen with the naked eye (and appropriate protective solar glasses). Our task now will be to reproduce this experience within celestia.