RR Lyrae stars are a type of pulsating variable star that are found in the Milky Way galaxy. They are relatively old stars, with ages of around 10 billion years. RR Lyrae stars are also relatively small, with masses of around half the mass of the Sun.

One way to weigh an RR Lyrae star is to use its pulsations. RR Lyrae stars pulsate in a regular pattern, and the period of pulsation is related to the mass of the star. The more massive the star, the shorter the period of pulsation.

By measuring the period of pulsation of an RR Lyrae star, astronomers can estimate its mass. This method is only accurate for stars that are relatively close to the Earth, as the pulsations become fainter with distance.

Another way to weigh an RR Lyrae star is to use its motion. RR Lyrae stars are moving through the Milky Way galaxy, and the speed of their motion is related to their mass. The more massive the star, the faster it moves.

By measuring the speed of motion of an RR Lyrae star, astronomers can estimate its mass. This method is only accurate for stars that are relatively close to the Earth, as the motion becomes fainter with distance.

By using these methods, astronomers have been able to weigh RR Lyrae stars and learn more about their properties. RR Lyrae stars are an important part of the Milky Way galaxy, and they play a role in the galaxy's evolution.