A special point in space in a three body system; the point at which one of the bodies is at rest in relation to the two others. Every planet has five Lagrangian points: three on a line defined by the planet and the star (Sun), and two on the planet's orbit, 60 degrees in either direction.
The Earth naturally has its Lagrangian points too.
SOHO orbits counter-clockwise around the L1 at the distance of 1,5 million kilometres (0,01 AU) from Earth. The period of this halo orbit is 178 days.
The existence of Lagrangian points was predicted by the French mathematician J.L. Lagrange in his 1788 book 'Mecanique analytique'. Lagrange had no illustrations in his book, because everything could be presented mathematically. We, however, shall use an illustration: the red dots represent the Lagrangian points of the blue planet.
