# Star expansion?

1. May 19, 2010

### meni ohana

Hi! my question is, if space expand, how come the stars (and planets) don't? they are part of the space and not "sitting inside" or somthing like that. meaning, the earth should grown bigger all the time.

you can think about marking a dot on a bloon, as you blow air inside the bloon starts to swell and the dot GETTING BIGGER AS WELL.

a related question, that might be answered by answering the last one, is if a star '90 light years' (random) away from earth send it's light rays toward us, and the space is spanding, then the conclusion is - by the time that light get to us, the planet will be maybe 150 light years away!

i need clarification
thanks!

2. May 19, 2010

### Mu naught

The expansion of the Universe is said to only occur on very very large scales - over galactic distances. As such, you would never be able to sense or measure it on such a small scale as the diameter of a star, or even 90 light years.

Also, just because the distance between two points in space is increasing, I don't think that means that locally an object has to be expanding with the space around it.

3. May 19, 2010

### mgb_phys

You can think of the expansion of the universe as a very weak force, individual stars and galaxies are held together by gravity. It's only between very distant galaxies where the gravitational force is very weak that the expansion of the universe is significant.

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