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Introduction to
Astrophysics and Cosmology
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GALAXY EVOLUTION
The picture here shows the various types of galaxies known, and a timeline showing their evolution. E stands for elliptical galaxies, where the integer following is representitive of how elliptical it is: E0 is very circular and round, whereas an E6 is more of an elongated circular shape (ellipse). S stands for spiral galaxies and SB for barred spiral galaxies, the differences of which can be observed in the photograph. The lowercase letter following the S or SB classification represents the length of the spiral arms of the galaxies.
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