The movement of Galaxies.

[wonderboy]

I don't know if this has been posed before or if anyone can help but I love astronomy, I love the beautiful pictures the mind boggling scenarios and the face that when you look at a galaxy, of which there are billions upon billions (i would imagine) that you are probably looking at (through default) millions of stars that have orbiting planets that contain life whether primitive or intelligent.

My question is, that with all the beautiful images available, how come there is no real time footage of a galaxy moving that can be found? im sure they move im sure i read that they do. surely there are galaxies far enough away that they can be observed moving clockwise or counter-clockwise? is this even possible, i.e are galaxies so big that their rate of movement looks sooooo slow? I dunno. I just want to see it.


Wonderboy!

[Chris Peterson]

My question is, that with all the beautiful images available, how come there is no real time footage of a galaxy moving that can be found? im sure they move im sure i read that they do. surely there are galaxies far enough away that they can be observed moving clockwise or counter-clockwise? is this even possible, i.e are galaxies so big that their rate of movement looks sooooo slow? I dunno. I just want to see it.

A galaxy has a typical rotation period on the order of 100 million years. We've been observing them closely for about 100 years, and most of the high resolution imagery is from the last 50 years or less. So the problem is that they simply haven't moved enough in the time we've been observing to actually see any change.

[wonderboy]

Thanks Chris.

I thought that would have been the answer. It's annoyed me for ages that. I bet its rotating really fast aswell, which makes it scary that its going to take it 100 million years to do one turn.

[Wayne]

Do some simple mathematics. Galaxies rotate as a unit (thanks, dark matter halo), so we can get angular velocity just from the radius and the rotational period.

The Milky Way rotates once every 200 million years (give or take) and it's 50,000 light years in radius. This means a star on the outer edge travels 2.pi.r distance in 200 million years. Evaluating that gives us 315,000 light years as the distance travelled in 200 million years.

This means they travel 0.00157 light years in one year, or 1.5E10 kilometers per year or 100 AU per year. 100 AU is roughly from one edge of Kuiper Belt to the other.

[wonderboy]

Thanks for that. it makes sense that something so big should look as if its moving so slow, even though its covering vast amounts of distance.

[The Code]

The Milky Way rotates once every 200 million years (give or take) and it's 50,000 light years in radius.

Pardon me.

http://en.wikipedia.org/wiki/Milky_Way


I always thought is was 100,000 light years across.

Mark

[Chris Peterson]

The Milky Way rotates once every 200 million years (give or take) and it's 50,000 light years in radius.

I always thought is was 100,000 light years across.

In other words, you two agree?

[Wayne]

Pardon me.

http://en.wikipedia.org/wiki/Milky_Way


I always thought is was 100,000 light years across.

Mark

Sorry for laughing at you like I am now... But tell me how radius relates to diameter?

[wonderboy]

This is quite funny haha

[The Code]

You was meant to laugh.
But, I posted the Wikipedia. Full details.
However. I only just noticed my error.

I always thought is was 100,000 light years across.

Tut Tut.

Mark