I made a simulator of the Solar System using Qt, VTK, and C++. Qt is an IDE for creating GUI applications using C++, and VTK is a library for 3D computer graphics, image processing, and visualization. The highlight of the simulator is the real mode where you can create a realistic Solar System from file, with actual physical parameters from which different properties of the planets can be observed. One such example could be: “How much longer is a year on Mars compared to that of on Earth?”.
The source code can be found in my Github.