Want to stay on top of all the space news? Follow @universetoday on Twitter
The Moon orbits the Earth and the Earth orbits the Sun, so does the Solar System orbit something? Yes, it orbits the center of the galaxy. At the center of the Milky Way is a supermassive black hole called Sagittarius A*. One Solar System orbit takes 220 million years.
The Milky Way is a barred spiral galaxy that fits into Hubble type Sb or Sc . That means that it is a spiral galaxy with a central bar-shaped structure of stars. Bars are found in approximately two-thirds of the known spiral galaxies. The bars affect both the motion of both interstellar gas and stars in a spiral galaxy and can affect spiral arms. Bars are thought to be relative latecomers to the Universe. A study by NASA’s Hubble Space Telescope shows that barred spiral galaxies were somewhat rare 7 billion years ago. The bars seem to be a sign of maturity for a galaxy.
Given that humans are the only intelligent life known in this Solar System, it is easy to think that the Milky Way is pretty small and empty. It is not. There are at least 200 billion stars in our galaxy and about 50 billion planets in orbit about them. Scientists estimate that 50 million of those planets could be in the habitable zone of their stars. The galaxy is approximately 100,000 light years across. It has a mass that is about 750 billion solar masses.
The Milky Way Galaxy belongs to the Local Group of galaxies. This group contains, 3 large and over 30 small galaxies. The Milky Way is the second largest (Andromeda is the largest) galaxy, but perhaps the most massive member of this group. Several of the dwarf Local Group members are companions of our galaxy. Our closest galactic neighbor, the Canis Major Dwarf, was just discovered in 2003. It is about 25,000 light-years away from us. This galaxy is currently in a close encounter with ours and has sections of its orbit within the volume occupied by the Milky Way.
Everything in the Universe seems to orbit something. The Solar System orbit is around the supermassive black hole Sagittarius A* and takes 220 million years to complete(a galactic year). In those terms our Solar System is very young at 21 galactic years and has only orbited 62 times since the beginning of the Universe 13.7 billion years ago.
We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.