Solar-mass
The solar mass (M☉) is a standard unit of mass in astronomy, equal to approximately 1.99 × 1030kilograms. It is used to indicate the masses of other stars, as well as clusters, nebulae and galaxies. It is equal to the mass of the Sun, about two nonillion (two quintillion in the long scale) kilograms:
The above mass is about 332946 times the mass of Earth (M⊕), or 1048 times the mass of Jupiter (MJ).
Because Earth follows an elliptical orbit around the Sun, its solar mass can be computed from the equation for the orbital period of a small body orbiting a central mass. Based upon the length of the year, the distance from Earth to the Sun (an astronomical unit or AU), and the gravitational constant (G), the mass of the Sun is given by:
The value of the gravitational constant was first derived from measurements that were made by Henry Cavendish in 1798 with a torsion balance. The value he obtained differs by only 1% from the modern value. The diurnal parallax of the Sun was accurately measured during the transits of Venus in 1761 and 1769, yielding a value of 9″ (9 arcseconds, compared to the present 1976 value of 8.794148″). From the value of the diurnal parallax, one can determine the distance to the Sun from the geometry of Earth.
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