This is because the relative mass of another planet in the Solar System or the combined mass of two binary stars can be calculated in units of Solar mass directly from the orbital radius and orbital period of the planet or stars using Kepler's third law, provided that orbital radius is measured in astronomical units and orbital period is measured in years.
Hal ini karena massa relatif planet lain di tata surya atau massa gabungan dari dua bintang biner dapat dihitung dalam satuan Surya massa langsung dari radius orbit dan periode orbit planet atau bintang menggunakan hukum ketiga Kepler, asalkan orbital radius diukur dalam satuan astronomi dan periode orbit diukur dalam tahun.