In message , Benoît
Morrissette writes
It was Edwin Hubble who first resolved individual stars in the Andromeda
galaxy in 1923.
http://home.cwru.edu/~sjr16/20th_people_hubble.html

He could only resolve the super giants but that was enough for him to find a
few cepheids wich gave him a way to measure the distqance and to proove that
the "Andromeda nebulae" was in fact a real galaxy with real stars. Before
that, it was believed that those "spiral nebulaes" were clouds of gas in our
own galaxy.

An other proof is given by sir Isaac Newton: using spectroscopy analysis, we
can measure the rotation speed of galaxies about themselves and around other
galaxies. Gas alone do not have enough mass to account for the
gravitationnal force that do that. Only billions of stars can do that.

While i think about that: we can see those galaxies, right? Where do you
think the "light" comes from? Clouds of gas do not emit light, stars do...

Surely not?? What about the Orion Nebula and its big brother in the
Large Magellanic cloud? I'm not too sure about your second proof either.
Haven't "galaxies" recently been found that do appear to be just gas
clouds, without stars? Though I do know that spectroscopy shows that M31
and most other galaxies are made of stars like our own Sun, rather than
gas clouds.
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Save the Hubble Space Telescope!
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