Absolute Magnitude

If we want to compare the actual brightness (luminosity) of all stars then we should do as if they were at the same distance from Earth.

1. Why?

2. What standard distance is chosen to compare the brightness of stars? ( in light years and parsecs)

3. If we know how far away a star is in parsecs, d, and its apparent magnitude, m, then we can calculate its luminosity using the equation

M = m + 5 - 5 log10 d

In any question you get d will be a power of 10 so log10 d will be easy to find, e.g. 100 = 102   so    log10 100 = 2

4. Complete this table

Star m distance (parsecs) M
a 2.4 10  
b 4.1 100  
c 3.7 1,000  
d 4.5 10,000  
e 5.5 100,000