Measuring the mass of a star now only takes two things: a planet and a moon.

David M. Kipping, a predoctoral fellow at the Harvard-Smithsonian Center for Astrophysics, has developed a new method to measure the mass of a star when provided information about the planets and moons orbiting the star.

The findings, published online earlier this month in the Monthly Notices of the Royal Astronomical Society Letters, will allow researchers to calculate the star’s mass with greater precision, according to Kipping. Previously, astronomers measured the temperature and age of the star to estimate its mass.

With Kipping’s method, researchers can measure the diameters, orbit radii, and orbit periods of the planet and moon. Then, Kepler’s third law of planetary motion can be used to derive the mass of the star.

“It was one of those papers where you get struck by an idea and you sit down late at night and do the math,” said Kipping, who researches exoplanets and exomoons, which are planets and moons outside of the Earth’s solar system.

Kipping has yet to use his method, as no exomoons have been discovered yet. But that may change in the near future, according to Laird M. Close, an astronomy professor at the University of Arizona and an exoplanet expert.

Close said that NASA’s Kepler spacecraft—an observatory launched in March 2009 that seeks to find earth-like exoplanets—has the ability to detect exomoons. Researchers have discovered more than 90 transiting exoplanets and confirmed the existence of more than 400 others.

Close said that Kipping’s method would allow researchers to confirm estimates and calibrate the models they use to measure the mass of a star.

“That’s what science is about—checking your assumptions,” Close said.

While Close said that Kipping’s method is a “difficult way to find the mass of a star,” he added it would likely still be accessible to undergraduate astronomy and physics students.