How many moles of stars are in the known universe?

Let's work through a rough calculation of the number of Sun-like stars in the Universe. There are approximately 200 billion Sun-like stars in the Milky Way, and about the same number of galaxies in the observable Universe. So, let's say that the total number of stars in the observable Universe is about (200 billion) x (200 billion), or about 4x10^22 (four times ten to the 22) stars. A mole is defined as 6x10^23 of something, so a mole of stars is 6x10^23 stars. If we compare this number to our estimate of the total number of stars, we find that there is about 1/10 of a mole of stars in the Universe.

Needless to say, although moles are a good unit to use when dealing with atoms and molecules, there are fewer moles of stars in the Universe than you might think...