# What Is Solar Mass?

A solar mass is the mass of the sun. Or, more precisely, it's 1.989 x 10^30 kilograms — about 333,000 Earths.

Astronomers use a solar mass as a basic unit of mass. Since most things in space are big and heavy — such as stars, galaxies and black holes — it makes more sense to talk about such cosmic objects in terms of solar masses as opposed to a much smaller unit, such as kilograms.

Thinking about objects in terms of solar masses also provides a more intuitive sense of the object's mass relative to the sun. The supermassive black hole at the center of the Milky Way galaxy, for example, is about 7.956 x 10^36 kg. Such a huge number is a bit harder to imagine than if you were to say the black hole is as massive as 4 million suns.

Thanks to Sir Isaac Newton, calculating the sun's mass isn't too hard, either. The sun's mass determines how strong its gravity is. And its gravity determines the orbital distance and speed of a planet like Earth.

For example, if the sun were more massive with a stronger gravitational pull, and if Earth were at the same distance from the sun, our planet would have to orbit faster or it would fall into the sun. If the sun were less massive with a weaker gravitational pull, Earth would have to orbit slower or it would be flung out of the solar system.

Newton's equations will calculate the sun's mass as long as we know the speed of Earth's orbit and the distance to the sun. Astronomers use basic geometry to calculate those two constants. Earth orbits the sun at about 67,000 mph (107,000 km/h), according to Cornell, and the distance from Earth to the sun (called an astronomical unit) is 92,955,807 miles (149,597,870 kilometers) according to the International Astronomers Union.