FlightGear is an open-source flight simulator. The goal of the FlightGear project is to create a sophisticated and open flight simulator framework for use in research or academic environments, pilot training, as an industry engineering tool, for DIY-ers to pursue their favorite interesting flight simulation idea, and last but certainly not least as a fun, realistic, and challenging desktop flight simulator. FlightGear implements extremely accurate time of day modeling with correctly placed sun, moon, stars, and planets for the specified time and date. FlightGear can track the current computer clock time in order to correctly place the sun, moon, and stars in their current and proper place relative to the earth. FlightGear has the ability to model a wide variety of aircraft. FlightGear allows users and aircraft designers access to a large number of internal state variables via numerous internal and external access mechanisms.