When did scientists know that the Milky way Galaxy is not the only galaxy in the universe?

Question

Meaning that there are other galaxies in the universe...

And by scientists, I mean any scientist. Whether it be a scientist from NASA, the European Space Agency (ESA) or anywhere else.

And what was the name of the scientist who made this discovery?

Answer 1

It is quite true that Hubble was the first to show that this was true, but the idea had been around for a long time.  It was first proposed in 1755 by Immanuel Kant.  

Answer 2

In 1923 Edwin Hubble found what he thought was a "spiral nebula" to be inside our galaxy. It was later classified as a galaxy, existing outside our galaxy. It was the first observed galaxy by a telescope.

Answer 3

In areas of thought one can say anything, but only in science do you actually need to show evidence that you are right. So Kant should be given some credit but actually showing that the nebulae were galaxies required a lot of work: red shift, Cephid variable observations etc.  

Answer 4

Ken is right. Hubble's observations simply confirmed what many people had long suspected, but could not prove. I think the turning point was the "Great Debate" between two prominent Astronomers: Harlow Shapley and Heber Curtis.

Shapley's contention was that the Milky Way was the only galaxy in the universe, whereas Curtis argued that the "spiral nebulae" were in fact other galaxies - "island universes". Hubble's observation of Cepheid Variable stars in the Andromeda "nebula" allowed him to demonstrate that Andromeda was incredibly distant, so as to put it way beyond the boundaries of our own galaxy.

Please read the website below, it has an excellent break-down of the Great Debate and will answer your question more fully.

Answer 5

Although the Andromeda Galaxy had been known and observed for centuries, it wasn't until Edwin Hubble's work on Cephid variables in M31 led to the astounding realization that, the (then called) Andromeda "Nebula" could not possibly be a part of the Milky Way.  If the Milky Way is only 100,000 light years across, how could this object be 2.5 Million light years away???

This was in 1923.  

In 1929, he "wowed" the astronomy community more when he detected that galaxies were "redshifting" away from us and each other, hence, all the support for an expanding universe.

Answer 6

^ Like they said, it was Hubble looking at what was then called the Andromeda Nebula, but we now call the Andromeda Galaxy.