other galaxies essays

other galaxies essays The visible universe is estimated to contain 50 billion galaxies. We are located in the Orion arm of the Milky Way galaxy. The Milky Way is a spiral galaxy, consisting of four arms that reach out from a central bulge of stars. Besides the Orion arm where the solar system containing earth is located, the other three arms are the Sagittarius arm, the Centaurs arm, and the Persius arm. But there are other types of galaxies in the universe, different from the spiral galaxy. Astronomers use the Hubble classification method to identify galaxies. The classes of galaxy are Spirals, Barred Spirals, Ellipticals, and Irregulars. Edwin Hubble found that a Spiral Galaxy is characteristic of a nuclear bulge and twisting trails of stars and glowing interstellar clouds of dust. What varies in a Spiral galaxy is the size of the nuclear bulge and how tight the arms are wound. But the two variables are related, the bigger the bulge, the tighter the arms. Spirals with tightly wound arms and a big bulge are called Sa (spiral type a), moderately wound arms with an average bulge are called SB, and galaxies with loosely wrapped arms and a tiny bulge Sc. There is one more variable to a Spiral galaxy; it can also be a barred Spiral, which means that the nuclear bulge has bars of stars running through it. Astronomers believe this is more common in galaxies that have less dark matter. A barred spiral galaxy is classified using the same types as unbarred spirals, but they are titled SBa, SBb, and SBc depending on the winding of their arms and the size of the bulge. All galaxies discovered to date move with the arms trailing the rotation of the galaxy; except one (NGC-4622), which is lead by the points of its arms. Elliptical galaxies are named for their round look. Hubble subdivided elliptical galaxies according to how round or oval they appear. E0 galaxies are the roundest, while E7 Galaxies are the most elongated. The Hubble method of clas...