Stellar mass is a term used in astronomy to describe how much mass is in a star. Scientists often measure this mass by comparing it to the mass of the Sun, which is called a solar mass (M☉) For example, the star Sirius has about 2.02 times the mass of the Sun, which is written as 2.02 M☉.[1] A star's mass will change over its lifetime because mass is lost with the stellar wind or thrown out by pulsational behavior, or if extra mass is accreted, such as from a binary star.