No Rigel is a huge, blue supergiant of spectral class B8 Ia, Rigel has an intrinsic brightness about 40,000 times as luminous as that of the sun.

The Hertzsprung-Russell diagram is a scatter graph of known stars. It shows the absolute magnitudes (actual brightness at a set distance) versus the spectral type or classification (which is effectively what their temperature is). Stars, when plotted onto this graph, tend to fall into set patterns. The position of a star within a pattern (or sequence) can give further information, such as how old the star is.

It may be just about anything. The apparent magnitude tells us how bright the star looks to us, not how bright it really is. The apparent magnitude (or brightness) depends both on the absolute magnitude (real brightness), but also depends on the star's distance.

Essentially it's 'brightness' on the vertical scale and colour on the horizontal scale. The brightness can be expressed as luminosity, compared with our suns luminosity, or as absolute magnitude. The colour can also be expressed in terms of temperature, the colour shows what the temperature is. The colour can be categorised in to groups or spectral classes.

The H-R diagram compares a star's surface temperature to its absolute brightness.