Ask A Scientist© Astronomy Archive

Author:      janette l gubala
How bright do stars shine?  

Response #:  1 of 2
Author:      samuel p bowen
The amount of light a star emits depends on how much nuclear fuel is being
consumed and on whether any of the emitted light can escape the surface of
the star.  The light a star emits during its lifetime will change.  When a
star exhausts its nuclear fuel, it can expand and become a red giant, or it
can collapse and become a black hole.  There is lots known about stars and
the life they evolve through.

Response #:  2 of 2
Author:      hawley
The brightness of stars as seen from the Earth is called "apparent visual
magnitude"; it is designated by "m subscript v" and is a logarithmic scale
like the Richter scale used for earthquakes.  The brightest star seen from
the Earth's northern hemisphere is Sirius, the Dog Star with a _m subscript
v_ of -1.5 (the stellar magnitude scale is one in which a negative number is
brighter than a positive number).  The absolute visual magnitude, designated
by "M subscript v", gives the true brightness:
Deneb (alpha Cygnus) has Mv = -6.9, and Rigel (beta Orion) is almost as
bright with Mv = -6.8.  On the absolute scale, Sirius is only Mv = +1.4; it
appears to be the brightest because of its nearby distance, only 2.65
parsecs.