# Orbits of Planets and Satellites

## Orbits of Planets and Satellites

**Basics of Orbit**

- An
**orbit**is the curved path that an object, such as a planet or a satellite, follows around another object due to the force of gravity. - This gravitational force provides the necessary centripetal force to keep the object in the curved path of orbit.

**Newton’s Law of Universal Gravitation**

**Newton’s Law of Universal Gravitation**states that every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.- This law underpins the concept of orbit. The gravitational force between the two objects keeps them orbiting around the center of mass.

**Elliptical Orbits**

- Both planets and satellites typically move in
**elliptical orbits**, not perfect circles. - Johannes Kepler first discovered this and it was later proven by Newton’s law of gravitation.
- An elliptical orbit means that the distance between the orbiting body and the body it’s orbiting changes as it follows its path.
- The closest point to the body being orbited is called
**perigee**, and the furthest point is called**apogee**.

**Kepler’s Laws**

- Kepler’s First Law (The Law of Orbits): All planets move in elliptical orbits with the sun at one focus.
- Kepler’s Second Law (The Law of Areas): An imaginary line drawn from the centre of the sun to the centre of the planet will sweep out equal areas in equal intervals of time.
- Kepler’s Third Law (The Law of Periods): The square of the period of any planet is proportional to the cube of the semi-major axis of its orbit.

**Gravity and Orbital Speed**

**Orbital speed**is the speed at which an object needs to travel to stay in orbit and is determined by the gravitational force acting upon it.- Less gravity requires a lower speed; more gravity requires a higher speed.
- The closer an object is to the body it is orbiting, the stronger the gravitational force and the faster the required orbital speed.

**Geostationary Satellites**

**Geostationary satellites**orbit around the Earth’s equator at the same rate the Earth rotates. This means they almost stand still relative to an observer on Earth’s surface.- These are typically positioned 35,786 kilometers above the Earth’s equator. At this height, one orbit takes 24 hours.
- They are commonly used for weather monitoring, telecommunications, and satellite TV.