Observations: AstronomyCast The Milky Way

The Milky Way is the galaxy that contains the Earth. The Milky Way is a barred spiral galaxy 100,000–120,000 light-years in diameter containing 200–400 billion stars. It may contain at least as many planets, with an estimated 10 billion of those orbiting in the habitable zone of their parent stars. It appears as a flat disk. The Solar System is located within the disk, around two thirds of the way out from the Galactic Center, on the inner edge of a spiral-shaped concentration of gas and dust called the Orion–Cygnus Arm. As a guide to the relative physical scale of the Milky Way, if it were reduced to 100 meters (110 yd) in diameter, the Solar System, including the hypothesized Oort cloud, would be no more than 1 millimeter (0.039 in) in width, or a grain of sand in a sports field. This gives you a real feel for how large the universe truly is. With billions of galaxies in the Universe, our solar system is just a miniscule speck in just one of those billions and bilions of other galaxies. It is very humbling to think about how small one human being is in comparison to our own Milky Way galaxy and the Universe.