Life and Death of Stars
From so far away, it's hard to imagine that every twinkling star in the night sky is an enormous ball of gas, ferociously devouring millions of tonnes of hydrogen every second to emit vast quantities of energy across the universe. In fact it is only on the most intense of hot summer days that we can really appreciate the true ferocity of our own star, the Sun.
Just like living organisms, stars all have a life cycle which they carry out. They all start in the same way in clouds of dust and gas, however stars with a mass greater than the Chandrasekhar Limit (1.4 solar masses) will have much more violent endings of their lives - either exploding in a supernova or forming incredibly dense neutron stars or black holes.
Two stars in the night sky which look similar in "brightness" may be millions of light-years apart, yet due to the further star being brighter we can not tell the difference. This effect is an example of the two kinds of brightness - apparent magnitude (m), the brightness of an object as observed from Earth, and absolute magnitude (M), the brightness of an object as observed from a distance (d) of 10 parsecs. These are related by the equation:
M = m + 5 - 5 log d
We can also use the brightness of stars to work out what stage of their life they are in. By plotting luminosity (absolute magnitude) relative to the Sun against the temperature (obtained from known emissions of colours at specific temperatures) in what is known as a Hertzsprung-Russell Diagram, we get a very specific pattern where each stage has a specific region of the graph.