Optical magnitude

From Wikipedia, the free encyclopedia

An Optical Magnitude or simply magnitude is a measure of the brightness of astronomical objects as seen from a common reference point which in most cases is the Earth's surface. The system owes its origin to Eudoxus of Cnidus, noted Greek mathematician and astronomer who was a contemporary of Plato.

The star Vega is taken to have a magnitude of 0 and is used as the basis for assigning magnitude. It is a negative logarithmic scale (like the chemical pH) and thus brighter objects have more negative magnitudes. The Sun, brightest object in the sky, has a magnitude of -25. Thus, the Sun is 10 raised to 25 times brighter than Vega.