Asteroids' magnitudes

All asteroids' physical characteristics appear in an experimental formula where V, the observed relative magnitude of the asteroid is expressed as a function of the other parameters:

where:

H is the absolute magnitude of the asteroid (represents the intrinsic brightness for example in the V band)
is the distance between the asteroid and Earth (or the observer)
r is the distance from the asteroid and the Sun
is the angle between the lines of sight to Earth and the Sun as seen from the asteroid.
is a phase function that depends on the movements of the NEO

This formula is very useful in the study of asteroids since it gives an evaluation of the absolute magnitude H of the asteroid as a function of measurable parameters.

Once the absolute magnitude H of the asteroid is known, many other parameters of the asteroid can be calculated. In fact, H depends both on the size and on the albedo of the asteroid. Thus, if the albedo can be measured or inferred from other observations (for example giving an estimated value corresponding to the asteroid's spectral type) it is possible to evaluate the dimension of the object.