The Milky Way Galaxy

Our Milky Way Galaxy is a spiral galaxy that is about 100,000 light-years in diameter containing 200–400 billion stars. Our own Sun is just one of those stars. 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 called the Orion Arm. Stars and gas throughout the Galaxy rotate about the center at approximately the same speed, taking about 200 million years for one rotational cycle, and moving at a velocity of 552 to 630 km per second. At the center of the Milky Way, where it appears brightest, is a supermassive ‘black hole,’ measuring 4 million solar masses (i.e., 4 million times larger than our Sun).

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MWmodel

The Centre of the Milky Way

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