 In 1926, there were enough galaxies known for Edwin Hubble to create a morphological classification scheme. This is his diagram. His students called it the Hubble Tuning Fork. Hubble's scheme divides galaxies into three broad classes based on their visual appearance. Elliptical galaxies have smooth, featureless light distributions and appear as ellipses in images like Centaurus A. They are denoted by the letter E followed by the integer N, representing a degree of ellipticity. Spiral galaxies consist of a flattened disk with stars forming a spiral structure and a central concentration of stars known as the bulge like the whirlpool galaxy. They are given the symbol S or SB if it has a bar core followed by a letter A through C. As we move from A to C, the spiral arm structure becomes more open, the amount of dust in young stars decreases, and the central bulge of the galaxy decreases in size relative to the disk size. Lenticular galaxies also consist of a bright central bulge surrounded by an extended disk-like structure, but unlike spiral galaxies, the disks of lenticular galaxies have no visible spiral structure and are not actively forming stars in any significant quantity. NGC 2787 is an example of these. They are designated S0. These broad classes can be extended to enable finer distinctions of appearance and to encompass other types of galaxies such as irregular galaxies, which have no obvious regular structure, either disk-like or ellipsoidal. Large Magellanic Cloud is an example of this. Since Hubble, others have added characteristics such as bars, rings, and spiral arm characteristics.