Johannes Kepler (Weil der Stadt, 1571 – Regensburg, 1630), Imperial Mathematician in Prague under Rudolf II, formulates the first two laws of planetary motion in Astronomia Nova (1609): planetary orbits are ellipses with the Sun at one focus (1st law), and a planet's radius vector sweeps equal areas in equal times (2nd law). The third law — the square of the orbital period is proportional to the cube of the semi-major axis — appears in Harmonices Mundi (1619). All three laws are possible because Kepler gains access to Tycho Brahe's body of observations, whose widow and heirs tried to block his access. Kepler spends five years analyzing Mars's orbit to rule out the circle and accept the ellipse. Kepler's laws are the empirical bridge between Brahe's observations and Newton's dynamics: the law of universal gravitation explains why Keplerian orbits have the shape they do.