What are some alternatives?
When comparing Space Engine and Gaia Sky, you can also consider the following products
Stellarium - Stellarium is a free open source planetarium for your computer.
Celestia - Celestia - real-time 3D visualization of space.
Solar System Scope - 3D model of the Solar System and night sky in real time
KStars - KStars is a Desktop Planetarium for KDE.
Sky Map - Sky Map (formerly the Google Sky Map) turns your Android-powered mobile phone into a window on the...
Universe Sandbox - Universe Sandbox ² is a physics-based space simulator.