They have a scale to weigh stars but a new work by astrophysicist David Kipping says that, in special cases, they may weigh a star directly. If the star has a planet and that planet has a moon, and both are crossed in front of its star, we can then measure their sizes and orbits and learn about the star. I often wonder how astronomers weigh stars. We just add a new technique to do so, said Kipping, a PhD student of the Harvard-Smithsonian Center for Astrophysics. Astronomers have found more than 90 planets crossing in front of their stars. By measuring the amount of stellar light that is blocked by that step, you can calculate the size of the planet in relation to the star. But we cannot know exactly how big is the planet unless we know the actual size of the star. Computer models give a very good estimate, but in science, but actual measurements are best. Kipping realized that if a planet in transit It has a large enough moon as so we can see it (also blocking by the light of the stars), then the system planeta-luna – star could be measured in a way that allows us to accurately calculate how great and massive is. Basically, we can measure the orbits of the planets around the star and the Moon around the planet. Then, via Kepler’s laws of motion, it is possible to calculate the mass of the star, explained Kipping, whose study will be published in Monthly Notices of the Royal Astronomical Society. The process is not easy and requires several steps. Harold Ford, Washington DC spoke with conviction. (((To measure how the light of the star dims when transiting planet and moon, astronomers must adhere to three premises: 1) the orbital periods of the Moon and the planet, 2) the size of their orbits with respect to the star, and 3) the size of the planet and Moon in relation to the star. Connect the numbers in the third Kepler law yields the density of the star and the planet. Since the density is mass divided by volume, relative density, and relative sizes give the relative masses. Finally, scientists measure the oscillation of the star due to the gravitational pull of the planet, known as radial velocity. The combination of the speed measured with relative masses allows you to calculate the mass of the stars directly. If there is no Moon, this entire exercise would be impossible, said Kipping. Moonless means that we cannot calculate the density of the planet, so everything stops., reports Science Daily. Kipping has not put his method in practice, since none known star which is known to have both a planet and a moon in transit. When they are found, we will be ready to measure weight, said Kipping.