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The Universe (Astrophysics) (We are part of the Milky Way Galaxy (The…
The Universe (Astrophysics)
We are part of the Milky Way Galaxy
The distance between neighbouring stars in the galaxy is often millions of times greater than the distance between planets in our solar system.
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.
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.
Galaxies themselves are often millions of times further apart than the stars are within a galaxy.
A galaxy is a large collection of stars.
So the universe is mostly empty space and is really big.
The universe is a large collection of billions of galaxies.
Our solar system has one star - The Sun
Our solar system is all the stuff that orbits the Sun. This includes things like:
Moons - these orbit planets with almost circular orbits. They're a type of natural satellite.
Artificial satellites usually orbit the Earth in fairly circular orbits.
Dwarf planets, like Pluto are planet-like objects that aren't big enough to be planets.
Asteroids - lumps of rock and metal that orbits the Sun. They're usually found in the asteroid belt.
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.
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.
Gravity provides the force that creates orbits
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.
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.
The force causing this is centripetal force. It acts towards the centre of the circle.
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.
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.
Satellites are kept in their orbits around planets by the gravitational attraction of the planet
The planets move around the Sun in almost circular orbit.