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Published on Jun 26, 2016
A short video looking at the movement of the planets in their orbits and the movement of the Sun and the rest of the Solar System around the centre of our galaxy, the Milky Way.
We look at how we have got to a heliocentric model of the Solar System and the nature of the orbits of the planets as they revolve around the Sun.
Then, with the help of some animations, we look at how the planets move in space due to the combined movement of their orbits around the Sun with the movement of the Solar System in its orbit around the centre of the Milky Way.
The Sun, and the Solar System with it, orbits the centre of the Milky Way once roughly every 225 million years. This is a huge span of time and is known as a Galactic Year. One Galactic Year ago was around when the Dinosaurs started evolving. The Solar System travels at around 230 km per second as it orbits the centre of the galaxy.
The orbits of the planets are all at an inclination to each other - which means that they are not all on the same planes. With the exception of Mercury , these inclinations are relatively small on the scale of the animations depicted and so in practise would not make any practical difference.
In a similar way, in the animations, the orbits of the planets have been simplified to circles rather than ellipses. At the scale shown in the animation, showing them as ellipses would not make a noticeable difference. The only possible exception would be Mercury, which has a more elliptical orbit than the other planets. Even then, at this scale it would be difficult to see any difference, but it is worth remembering this point.
As the Solar System orbits the centre of the Milky Way galaxy, it also gently and slowly oscillates up and down in the plane of its orbit. It does this around four times during one orbit of the centre. As a result, for the purposes of these animations, the movement of the Solar System is basically a straight line.
As the Sun orbits the centre of the Milky Way, the Solar System is tilted over at 60 degrees, so sometimes one or more of the planets will "lead" the Sun whilst the others are behind it.
The stars are just a space background texture to show the movement of the camera position and are not to be taken to be the true position of the stars. The animation is speeded up so that one minute of the animation is about twenty years of real time.
This video is in large part thanks to inspiration and information provided by Phil Plait (the "Bad Astronomer") and I am very grateful to him. I must point out any inaccuracies are down to me!