The Morphology of Galaxies: The Hubble Sequence
(We are starting on Chapter 16 now!)
First, it should be realized, the existence of other galaxies
such as our own, was not fully recognized until about 60 years ago.
A famous debate occurred in 1920 between
|
Harlow Shapley |
|
Heber Curtis |
Shapley and Curtis argued over the ``Scale of the Universe." Curtis argued that the Universe is composed of many galaxies like our own, which had been identified by astronomers of his time as ``spiral nebulae". Shapley argued that these ``spiral nebulae" were just nearby gas clouds, and that the Universe was composed of only one big Galaxy. In Shapley's model, our Sun was far from the center of this Great Universe/Galaxy. In contrast, Curtis placed our Sun near the center of our relatively small Galaxy.
With time, both were shown to be right AND wrong:
Shapley was proved more correct about the size of our Galaxy and the Sun's location in it, but Curtis was proved correct that our Universe was composed of many more galaxies, and that ``spiral nebulae" were indeed galaxies just like our own.