Orbital Motion
- There are many orbiting objects in our solar system and they each orbit a different type of planetary body
Orbiting Objects or Bodies in Our Solar System Table
- A smaller body or object will orbit a larger body
- For example, a planet orbiting a Sun
- In order to orbit a body such as a star or a planet, there has to be a force pulling things towards that body
- Gravity provides this force
- The gravitational force exerted by the larger body on the orbiting object is always attractive
- Therefore, the gravitational force always acts towards the centre of the larger body
- The gravitational force will cause the body to move and maintain in a circular path
Gravitational attraction causes the Moon to orbit around the Earth
- Gravity causes different astronomical orbits to orbit certain others
- In general:
- Planets orbit the Sun
- Moons orbit planets
- Comets orbit the Sun
- Artificial satellites to orbit the Earth or any body in the Solar System
Differences in Orbits
Orbits of Planets
- There are several similarities in the way different planets orbit the Sun:
- Their orbits are all slightly elliptical (stretched circles) with the Sun at one focus (approximately the centre of the orbit)
- They all orbit in the same plane
- They all travel the same direction around the Sun
- There are also a few differences:
- They orbit at different distances from the Sun (different orbital radius)
- They orbit at different speeds
- They all take different amounts of time to orbit the Sun
- The further away a planet is from the Sun, the slower it travels and therefore the longer it takes to orbit
The orbits of planets around the Sun
Orbits of Moons
- Moons orbit planets in a circular path
- Some planets have more than one moon
- The closer the moon is to the planet:
- The shorter the time it will take to orbit
- The greater the speed of the orbit
Comets
- The orbits of comets are very different to those of planets:
- Their orbits are highly elliptical (very stretched) or hyperbolic
- This causes the speed of the comets to change significantly as their distance from the Sun changes
- Not all comets orbit in the same plane as the planets and some don’t even orbit in the same direction
- As the comet approaches the sun, its speed increases
- As it moves further away from the sun, its speed decreases
The elliptical orbit of a comet
