Artist's concept of Edwin Hubble's galaxy classification system, created to classify galaxies depending on their appearance, This system is sometimes called Hubble's Tuning Fork. At the left are elliptical galaxies, which are classified depending on how round they appear. The scale goes from E0 (the roundest) to E7, the most elliptical. Further to the right are lenticular galaxies, which are an intermediary class between ellipticals and spirals (classified SA0 or SB0, depending on if they have a bar at the core). To the right are the spiral galaxies, and they are classified depending on how tightly coiled (Sa, Sb and Sc) the spiral arms are (top branch), and if their core hosts a barred shape (bottom branch). The barred galaxies get the classification SBa, SBb and SBc, where SBa has the most tightly coiled arms.
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