Why does a dwarf differ from the main sequence stars?

We start by taking a look at the Hertzsprung -Russell(HR) diagram, which is basically a scatter plot of stars, in a luminosity v.s temperature grid. The main sequence is when the stars are in the hydrogen fusion stage,i.e hydrogen is fused to produce helium. read more

All main sequence stars share a vital characteristic: they generate virtually all of their energy from hydrogen fusion in the star's core. Other than that, they can all be very different. Mass, temperature, and chemical composition vary tremendously from Class O down to Class M. Oddly enough, a main sequence star is called a dwarf. read more

Cheeky answer: because they are smaller than giant stars. That said, I don't know if there is a definite cutoff point where main sequence stars are no longer called dwarfs. I would certainly not think of main sequence stars of spectral types A, B and O as dwarfs. read more

Scientists think that 20 out of the 30 stars nearest to Earth are red dwarfs; however, none of them can be seen with the naked eye. The closest star to the sun, Proxima Centauri, is a red dwarf. Despite its frequent appearance, the term "red dwarf" does not refer to a single kind of star. read more