A Magnitude is the measure of
brightness of a
celestial object. It is a logarithm scale that is
used to determine levels of
brightness between other
stars. The ratio of apparent
brightness between two
stars is:
There are actually two types of
Magnitude: apparent and absolute. Apparent magnitude
is the how bright a
star looks from
Earth. Absolute
magnitude is the true
brightness of a
star.
When comparing the apparent and
absolute magnitude of a
star, we get what is called
the Distance Modulus:
This is actually a very powerful
equation in that if we know the absolute and
apparent magnitude of a
star, we can determine its
distance - and its pretty accurate too.
In addition to comparing
stars, we
can also compare color ratios between stars to
learn surface
temperature. This color ratio is also
called a
B-V ratio (B=blue, V=visual or green) that
is determined by using filters (Blue and Green in
this case):
For example, a star with a
V < B ratio, the
surface temperature is higher than a
star with a
V >
B ratio. As a note, other filters can be (and often
are) used.
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