Calculating motions in the Solar System – basic principles
How it works
In the Solar System, planets and other celestial bodies move in orbits around the Sun. For orbits around the same central body, the orbital period depends on the size of the orbit (Kepler's laws). The speed of a celestial body on an elliptical orbit is not constant, but is greatest at the point closest to the Sun and smallest at the point farthest from the Sun. The Sun's gravitational force keeps the celestial bodies in their orbits. Mean orbital speed and orbital period can be calculated using known formulas. Comparing the orbital periods and orbit sizes of different planets shows the regularities of planetary motion.
For celestial bodies orbiting the Sun, according to the 3. Kepler's law: The square of the orbital period T is proportional to the third power of the semimajor axis a of the orbit: T^2 ∝ a^3. For circular orbits, a corresponds to the orbital radius r.
An example
A planet has a semimajor axis that is twice as large as that of Earth. How many times longer does its orbit around the Sun take?
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50 Exercises
To the learning unit →Own explanation and own practice exercises by AmyMath. Subject reference framework: Astronomy. The topic assignment may vary by federal state.