# Is everything in space spinning in the same direction?

19 April 2016

## Question

Do the bodies floating in space - be they stars, planets of whatever - have different spinning directions - that is are some spinning clockwise and others ant-clockwise while some are doing up down type of spinning orientation? Or is everything spinning in the same direction?

Kat Arney put this question to Cambridge astronomer Matt Middleton...

Matt - Okay. So the basis of this is conservation of angular momentum, which most of us will probably be familiar with if we watch Tom Daly dive, and hopefully win gold at Rio. Kat - It's all about the angular momentum, obviously.

Matt - Is it really. So, as a diver, be it Tom Daly or any of the other favourites, tucked in they spin around faster, if they open up they spin around slower, so thats conservation of angular momentum in action. Chris - The other example is a ballerina.

Matt - A ballerina is a really good example...

Chris - A ballerina or an ice skater when they're doing a pirouette.

Matt - Chris, whatever you're the biggest fan of really. Kat - Anyway, back to the physics. We've got things spinning round.

Chris - Other heavenly bodies to talk about out in space Matt, yes.

Kat - So we've got stuff like spinning round?

Matt - Yes, okay. So a star forms from something called a protostellar disc. So you have a molecular cloud - these big things everyone's probably seen pictures of something like the Horsehead Nebula. These beautiful massive columns of gas and then, eventually, a star will form when the gas cools and it actually begins to rotate. When it begins to rotate it actually flattens and forms a disc and in the centre you've got a newborn star. That disc is rotating and it's going to be rotating in the same direction that the star is rotating because you're conserving angular momentum.

Kat - What makes it start rotating in the first place. Is it just like whatever random wobble is there?

Matt - It's random motions that start because you start hitting things over and over again. They all start moving with the overall angular momentum.

Chris - It's like the average. That all the particles that come to the party to make the star, they add all of their own bit of spin and the average, when you sum it all up, some going one way, some going the other, will end up being in one direction, another band...

Matt - It all part of that collapse and that movement is a . yes. Kat - But within that kind of solar system would all the planets be spinning the same way? And what about our own solar system - is everything spinning the same way in our own solar system?

Matt - So many questions. Okay. So, this disc of gas it cools, it forms planets. They have their own little discs and therefore they're going to be travelling in the same direction. So, in a perfect scenario you'd have a star in the middle rotating in one direction. The planets will then also all be going round in the same direction, the same direction that disc was going and the planets will also be spinning in the same direction as the central star. But - and I can use Chris as this. Chris look at me. Okay.

So for me, I'm rotating this clockwise but what direction does it look like for you?

Chris - Well you're turning a biro over and over in you hand and you're saying.

Matt - It's not a biro it's an ink pen.

Chris - Okay and ink pen. You're turning it over and over in your hand - for you it's clockwise for me it's the other way round. It looks like it's turning anticlockwise.

Matt - So the way it looks to us is just a matter of perspective. To say that everything is spinning in the same direction, it doesn't really have any meaning. You have to put it in the perspective of the observer. But going back to our own solar system, there are, in fact, two planets that do not spin in the same direction - Venus and Uranus). We believe that they've just encountered another body.

Kat - Kind of like billiard ball smacking together? They've then spun off the other way round?

Matt - Yes. So, Uranus actually spins almost on it's axis and Venus spins in the other direction and so they may have well encountered in the very early period of our solar system another body may have struck it, it's transferred angular momentum, it's now spinning in a different direction. So certainly in our own system there's evidence that things don't have to spin in the same direction. Kat - Fair enough...