Celestia is a free, real-time 3D visualization of space software that allows users to explore our universe in three dimensions. Available on Windows, Linux, MacOS, iOS, and Android, Celestia offers a unique and immersive experience that sets it apart from other planetarium software.

One of the main features of Celestia is its ability to take users beyond the surface of the Earth. With the program, you can travel throughout the solar system and visit over 100,000 stars, or even beyond the galaxy. The program features a smooth and seamless movement system that makes it easy to explore the universe, with an exponential zoom feature that lets you explore space across a huge range of scales, from galaxy clusters down to spacecraft only a few meters across. The 'point-and-goto' interface also makes it simple to navigate through the universe to the object you want to visit.

Celestia also comes with a large catalog of stars, galaxies, planets, moons, asteroids, comets, and spacecraft, and it is expandable, with dozens of easy to install add-ons available that include more objects to visit. Additionally, the software allows users to add their own content, making it possible to construct whole planetary systems, nebulae, galaxies, or fictional objects.

Celestia also has interactive planetarium capabilities, allowing users to easily navigate to any world and land on its surface. When used as a planetarium, Celestia shows accurate positions of solar system objects in the sky, and users can switch labels and other supporting features on and off with hotkeys, or zoom in and out on an object of interest, for example Jupiter’s system of moons.

Other features of Celestia include Virtual Textures, which can be used to display extremely high-resolution textures or close-up features on planetary surfaces, with Celestia only loading the tiles it needs to display, increasing performance. Additionally, it has audio playing capabilities and supports different types of trajectory data, like Sampled Orbits for example can be used for spacecraft paths, or you can use NASA’s SPICE kernels for various solar system objects.

Overall, Celestia is a powerful and immersive space exploration software that offers users an unparalleled experience of exploring our universe in three dimensions. Its seamless movement system, expansive catalog of objects, and expandable content make it a must-have for anyone interested in space exploration and education. With its compatibility with different platforms and easy-to-use interface, Celestia is an excellent tool for all ages to learn and explore the universe in an interactive way.