There must be an invisible force that is acting on those galaxies. These two features make the accelerating universe the most probable explanation amongst its competitors (Riess 2012)
Second, looking along the equatorial plane, the closest stars are situated against a faint but luminous band, being "the blended light of billions of stars in the galaxy's disc. In 1785, astronomer William Herschel, by using a 48-inch reflector telescope of his own construction, counted the stars in more than 600 regions of the sky and concluded that "the majority are concentrated along a plane and that the galaxy is disc-shaped with the Sun at its center" (Parker, 1988, 156)
With the advent of large reflecting telescopes, such as the Mount Palomar reflector in the 1950's, it was determined that the distribution of stars in our galaxy was "shaped like a flattened disc similar to a double convex lens" and if viewed from above appeared "nearly circular with a concentration of stars in the center forming a spherical nucleus and other stars forming spiral arms." Thus, the entire structure has often been compared to a giant pinwheel (Pasachoff, 1990, 56)
In essence, the entire Milky Way galaxy is also moving and has been estimated to take some 3 billion years to make one complete revolution within the universe itself. In comparison, our Sun takes about 250 million years to complete one revolution around the center of the galaxy which is often referred to as a galactic year (Verschur, 1990, 178)
The term galaxy is used when a large group of stars, generally a billion or more, have clustered together due to a similar attraction to some gravitational attraction. The Milky Way Galaxy is actually a conglomeration of others such as the Canis Major Dwarf Galaxy and the Sagittarius Dwarf Galaxy whose masses have been consumed by the Milky Way (Wethington, 2009)