Betelgeuse is not very bright in the sky, but has a really large absolute magnitude. Why do you think this is? Find at least 2 reasons!

Sound waves travel faster in a low-density gas

Explanation:

First of all, let's remind that sound waves are pressure waves: they consist of oscillations of the particles in a medium, which oscillate back and forth along the direction of motion of the wave (longitudinal wave).

The speed of sound in an ideal gas is given by the equation

where

is the adiabatic index of the gas

p is the gas pressure

is the gas density

From the equation, we see that the speed of sound is inversely proportional to the square root of the density: therefore, the lower the density, the faster the sound waves.

So, sound waves will travel faster in a low-density gas.