What is apparent and absolute magnitude?
Magnitude is a measure of brightness on a logarithmic scale. The apparent magnitude (m) of a celestial body is a measure of its brightness as seen by an observer on Earth, normalized to the value it would have in the absence of the atmosphere. Absolute magnitude (M) is defined as the magnitude a star (or any other celestial object) would have if placed at an exact distance of 10 parsecs (32.6 light years) from us. (Wikipedia) The ‘distance modulus’ is the difference between the apparent magnitude and absolute magnitude of a celestial object (m – M), and provides a measure of the distance to the object, r.