the sun - Is the Sun really a medium size star?

It is true that a surprisingly large number of stars are smaller (and thus less massive) than the Sun. However, the stars that are bigger than the Sun are often much bigger.

Look at this chart:

^{Image courtesy of Wikipedia user Jcpag2012 under the Creative Commons Attribution-Share Alike 3.0 Unported license.}

Notice how small the Sun is compared to some of the other stars. It's tiny! It is indeed a small star - in technical terms a main sequence dwarf.

However, despite its size, it is clear that there are many more stars less massive than the Sun that there are stars more massive than the Sun. Why? There are two reasons:

1. Lower-mass stars live longer.


2. More low-mass stars can form in a given region than high-mass stars.

^{Encyclopedia of Astronomy and Astrophysics}

The distribution of masses can be quantified in an initial mass function, typically given in the form
$$xi(m)=km^{-alpha}$$

When you integrate this over a range of masses, you can find how many stars are within that range. Not surprisingly, this number gets lower and lower as you slide the endpoints to more massive stars. You can see this decrease from the fact that $xi'(m)<0$, so long as $k>0$ and $alpha>0$ - which is assumed by the model, according to empirical data.