Milky Way and Andromeda collision

[John]

http://www.telegraph.co.uk/sciencean...-expected.html

Interesting stuff this, and scary to think about, even though it is about 3 billion years away. But how do they know how fast the Milky Way moves? 600,000mph apparently... in what direction exactly? How do they measure its speed? Do they do it in comparison to other things outside the galaxy?

Is everything in these reports accurate, is, I guess, what I'm asking?

[MattR]

I don't know John, but unless they discover the secret of eternal life I wouldn't let it keep you up at night :D

[mathare]

It's mainly done by measuring light from distant galaxies etc etc. The speed of light is a constant so they can use that and doppler shifts I think to work these things out

[Win2Win]

They use red shifting to discover how fast things are moving towards/away from us.....or they just hold their fingers to the sky and measure it that way :)

[mathare]

They use red shifting to discover how fast things are movingg towards/away from us

As I said, doppler shifts on light

[Win2Win]

The Doppler effect covers a wide variety of waves, not redshift specifically.

[mathare]

Reshift is just a specific form of doppler shifting though. I was keeping it simple and generic :)

[MattR]

I was keeping it simple and generic :)

Generic maybe :D

[scoobydoo]

Let's hope Patrick Moore signs up in the next few days eh.

[vegyjones]

Speaking of Milky Way, I saw an old advert for it the other day.

Are they bringing the nouget filled one back? I used to like that, can't stomach the one with the white centre!

[mathare]

Generic maybe :D

Oops, sorry.

Either Wiki redshift/doppler shift and see what you can get from that, or...

Think about a police car with its siren blaring. The noise changes as the car approaches and then speeds past you, right? That's because the frequency of the soundwave changes as the car is moving relative to you. If you stand still on the street with a police car down the road to your left you'll hear the siren as a given noise. That noise will change as it gets nearer to you and when it goes past you'll hear the siren differently. That's doppler shifting. It affects light as well as sound so astrophysicists can measure light from a given galaxy (or whatever) and compare that to what it should be if everything is static. They can then tell that the galaxy is moving away from them as the light is redshifted in the same way as the police siren is as the car moves away from you. The degree of redshift can be determined so we then know how fast the universe is expanding.

That's not helped any has it?

[barrelmaniac]

Im not really going to worry about this too much, I will probably be dead by the time this happens anyway

[MattR]

Last one out turn off the light!


Actually Mat it did help a bit.

[bigmazey]

This is all very well but can the doppler shift predict what is going to win tommorrow.

Mabye its Final Approach 6.25 Leopardstown or Acrosstheuniverse 2.25 Warwick.

[Win2Win]

Due to the speed of light when you see a horse just before the line, it has actually passed it....as you brain does not process at the speed of light...so if you speed up your brain to lightspeed you'll know the result a billisecond () before everyone else

[MattR]

As comedian Stephen Wright once said; What happens if you are travelling at the speed off light and put your headlights on?

[Win2Win]

As comedian Stephen Wright once said; What happens if you are travelling at the speed off light and put your headlights on?

You see them as normal