The Universe (Astrophysics) (Gravity provides the force that creates…
The Universe (Astrophysics)
Gravity provides the force that creates orbits
The planets move around the Sun in almost circular orbit.
Satellites are kept in their orbits around planets by the gravitational attraction of the planet
If an object is travelling in a circle it is constantly changing direction (and so constantly accelerating), which means there must be a force acting on it.
The force that makes this happen is provided by gravitational force (gravity). The gravitational attraction of the Sun keeps the planets and comets in their orbits around it.
The force causing this is centripetal force. It acts towards the centre of the circle.
The object keeps accelerating towards what it's orbiting but the instantaneous velocity (which is at a right-angle to the acceleration) keeps it travelling in a circle.
This force would cause the object to fall towards whatever it was orbiting, but as the object is already moving, it just causes it to change direction.
Our solar system has one star - The Sun
Our solar system is all the stuff that orbits the Sun. This includes things like:
Comets - lumps of ice and dust that orbit the Sun. Their orbits are usually highly elliptical (a very stretched-out circle) - some travel from near to the Sun to the outskirts of the solar system.
Planets - these are large objects that orbit a star. The eight planets in our solar system are, in order (from the Sun outwards): Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Asteroids - lumps of rock and metal that orbits the Sun. They're usually found in the asteroid belt.
Dwarf planets, like Pluto are planet-like objects that aren't big enough to be planets.
Artificial satellites usually orbit the Earth in fairly circular orbits.
Moons - these orbit planets with almost circular orbits. They're a type of natural satellite.
We are part of the Milky Way Galaxy
The universe is a large collection of billions of galaxies.
So the universe is mostly empty space and is really big.
A galaxy is a large collection of stars.
Galaxies themselves are often millions of times further apart than the stars are within a galaxy.
Our Sun is just one of the many billion stars which form the Milky Way galaxy. Our Sun is about halfway along one of the spiral arms of the Milky Way.
The force which keeps the stars together in a galaxy is gravity. And like most things in the universe, galaxies rotate like a Catherine wheel.
The distance between neighbouring stars in the galaxy is often millions of times greater than the distance between planets in our solar system.