r_earth = 6378.137e3  # Earth equat. radius [m]
m_earth = 5.9742e24  # Earth mass [Kg]
c = 2.99792458e8  # speed of light [m/s]
# Earth rotation speed [rad/s] Groten 2004, adopted by the IERS in 2010 as the
# reference
Om_t = 7.292115 * 1e-5
g = 9.81  # Gravity constant [m/s^2]
