@article{Mueller:2011:NTG,
    author={Thomas Müller and Jörg Frauendiener},
    title={Studying null and time-like geodesics in the classroom},
    journal={European Journal of Physics},
    volume={32},
    number={3},
    pages={747},
    url={http://stacks.iop.org/0143-0807/32/i=3/a=011},
    year={2011}
}