Portal:Astronomy/Did you know/6

... that the asteroid 2011 XC2 missed the Earth by less than 1 lunar distance on 3 December 2011?
... that the mass-luminosity relation, first derived by Arthur Eddington in 1924, helps astronomers find the distances to binary star systems?
... that the planetary nebula Abell 39 is unusually spherical, yet its central star is offset from the center?
... that data from Mariner 10 led to the discovery of Mercury's magnetic field in 1974?
... that the Toronto Magnetic Observatory had to be moved as the University of Toronto's electric lighting was interfering with observations?