Pogson ratio (?p?d?s?n) n (Astronomy) the brightness ratio of two celestial objects that differ by one magnitude. On the Pogson scale a difference of 5 magnitudes is defined as a difference of 100 in the intensities of two stars; therefore a difference of 1 magnitude is equal to the fifth root of 100, i.e. 2.512[C19: named after N. R. Pogson (1829?91), British astronomer]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014