Astronomers use the term apparent magnitude to explain how luminous an object is from Earth in the sky. The idea of a scale of magnitude goes back to Hipparchus, who invented a scale to explain the brightness of the stars that he could see. He awarded the brightest stars in the sky an apparent magnitude of 1 and he gave the dimmest stars he could see an apparent magnitude of 6. His scheme does not contain the sun , moon or planets.
A astronomical object ‘s apparent magnitude, such as a star or planet, is the brightness that an observer is observing at a given distance from the source. The smaller the distance from the target to the viewer, the larger the apparent brightness.
Two objects with the same apparent magnitude as seen from the Planet may be either:-
- Of the same luminosity, at the same distance from the Planet.
- Or varying levels of luminosity, at various distances from the Planet.