
Period Calculator
An object's orbital period can be computed from its semimajor axis and the mass of the body it orbits using the following formula:

 a is the semimajor axis of the object
 P is the orbital period
 G is the gravitational constant
 M is the mass of the parent body

 Default units  Acceptable substitute units 
a  meters (m)  centimeters (cm), kilometers (km), miles (mi), feet (ft), Earth radii (Re), Solar radii (Rs), astronomical units (AU), light years (ly), parsec (pc)
 T  seconds (s)  minutes (m), hours (h), days (d), years (yr) 
G  N m^{2}kg^{2}  
M  kilograms (kg)  grams (g), Earth masses (Me), Solar masses (Ms) 
Sample problems:
1. A satellite orbits the Earth. It's semimajor axis is 7000 km. What is the satellite's orbital period in hours?
Enter 7000 km for a and 1 Me for M.
The calculator gives you an answer of 5830.318 s. Highlight the s and type h. It now gives you an answer of 1.6195 hr.

2. Astronomers discover a distant planet orbiting the Sun. It's semimajor axis is 1 light year. What is the planet's orbital period in years?
Enter 1 LY for a and 1 Ms for M.
The calculator gives you an answer of 501850205474964.06 s. Highlight the s and type y. It now gives you an answer of 15902421.421915896 yr.

 