Un peu d'Astronomie!

Gunn Interactive by Dereck and Arthur Gun
(BCom,Info Systems, Comp Sci Flash animation/programming expert)
(english version)

Clic sur l'image pour voir le système solaire
(flash interactif)

Step by step!

"This is a view of the solar-system which shows it as we understand it to be. The Sun is in the centre, and the planets orbit at varying speeds. Notice how the outer planets move much more slowly than the inner ones.

This is the same view with the orbits turned off.

If you watch the planets move across the sky from on earth, they can move in a funny way. So let's take a closer look.

Now, let's put the Earth in the centre.

This will give you an idea of the motions of the other planets from earths point of view. Early astronomers had to make their models of the solar system from what they could see and they had to make years of careful observations. Many at first assumed the Earth was the center of the Universe.

Now the planets still keeping to their orbits, but it looks odd as we are keeping the Earth in the middle. Let's turn on the orbits.

That makes things a bit clearer, we can see that the planets are indeed sticking to their orbits.

Now let's look at Venus. Can we see the path that Venus traces through the sky? Turning on trails will help..

Let's wait a minute and watch the trail form. It makes an interesting curve doesn't it? By chance, the relative speeds of Earth's and Venus's orbits mean that a 5 sided pattern emerges. See how venus seems to spend a lot of time moving slowly around the earth, and then quickly comes in, goes backwards, and the accelerates off again. This is called retrograde Motion. Lets see how close Venus gets.

Wow, at it's closest, Venus is 4 times closer to us than the sun! At its furthest it's about 1.72 times further away. We can make this more clear if we change the units...

Okay, now we are using Astronomical Units. An Astronomical Unit is the mean distance between the Earth and the Sun - 149,597,871 km. How useful!

Now we know about Retrorade motion. Let's look at something else, Jupiter's motion in the sky!

Jupiter moves much more slowly. It's year is 4,334.5 Earth days long - almost 12 Earth years. Let's increase the speed!

That's better. See how the curve forming has small circles. Because Jupiter moves so much more slowly than the earth, the main movement we see in Jupiter's position is from the Earths own movement. We can get a better idea of where we are if we show the other planets.

Neat. We'll be able to get an even better if we turn orbits on.

That's the end of the lesson!

Hopefully you learnt something new. Now try something by yourself - what would the Earth's motion look like to a martian?"