 Solar mass

The solar mass, written $M_{\odot }$, is a mass unit based on the Sun, approximately $1.99\times 10^{30}\mathrm{kg}$. Expressing stellar masses in this unit makes comparisons immediate: a $2M_{\odot }$ star has roughly twice the Sun's mass. It does not follow that it has twice the solar luminosity, because the mass-luminosity relation is nonlinear.

Orbital observations constrain the gravitational parameter $GM$ more directly than mass in kilograms. The nominal solar mass parameter supplies an exact conventional conversion for such comparisons; converting it to kilograms additionally requires the measured gravitational constant. A nominal constant is therefore distinct from claiming that the physical Sun's changing mass is known exactly.^[ref]

A solar mass (often denoted as \( M_\odot \)) is a standard unit of mass used in astronomy to measure the mass of stars and other astronomical objects. It is defined as the mass of the Sun, which is approximately \( 1.989 \times 10^{30} \) kilograms (or about \( 333,000 \) times the mass of Earth).