When astronomers are talking about different stars this is how they would they would refer to and classify them. So when you know the spectral type and luminosity of a star, it is easier to understand exactly what kind of star it actually is. Magnitude Astronomers measure a stars brightness on a scale of Magnitude . There are two ways to measure a stars magnitude. There is absolute magnitude and apparent magnitude.
Absolute magnitude is the actual brightness, or brilliance, of a star in outer space.
Apparent magnitude is how bright a star seems when seen from Earth. Another star, one that is actually dim, might appear brighter only because it is so close to Earth. On the Magnitude scale, the brightest stars are 0 magnitude or even minus magnitude. The higher the number is, the dimmer the star is.