[acapella34]

in my revision guide it says nearby galaxies all have similar patterns of lines in their emission and absorption spectra? why???
i asked my teacher whether its coz those galaxies are in the same phase in fusion ( for e.g. the galaxies were made roughly the same time so they are still fusing hydrogen in the stars they contain) but my teacher says you cant assume this
just coz galaxies are close to eachother doesnt mean they are nearly the same age and even if they are doesnt mean they are in the same stage of fusion - so wont have similar patterns of lines because it depends on the stars they contain in the galaxies which in turn depends on how much mass was initally available to form those stars - so this determines its stage in fusion i.e. whether its hydrogen/helium fusion.
so that brings me back to the original question why do galaxies nearby have similar patterns on lines in their absorption and emission spectra?

sorry for the long question but my revision guide is seriously annoying it just states facts and doesnt explain why it is so, thanks for taking the time to read this!

[EyesSetToKill]

Well most stars spend most of their life in the Main Sequence like our Sun, just fusing Hydrogen into Helium.
Therefore, on their atomic emission spectra they will have a similar pattern as it will show mainly H/He.

Also, as they are nearby galaxies they probably came to existence at a similar time because of the Big Bang. Of course this is some galaxies and is only an assumption.

Yeah I know what you mean, but in the end they are there just to guide you in your revision. Look in the text book if you are unsure.

Hope this helps, and just contact me if you need any more help! (Except on electric fields...I don't get them!)