The Milky Way Galaxy is about 80-100 thousand light years in diameter, about 3,000 light years in thickness, and about 250-300 thousand light years in circumference. It is composed of 200 to 400 billion stars (exact number not yet known). As a guide to the relative physical scale of the Milky Way, if the galaxy were reduced to 130 km (80 mi) in diameter, the solar system would be a mere 2 mm (0.08 in) in width.
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It would take the solar system about 225-250 million years [9] to complete one orbit ("galactic year"), and so is thought to have completed about 20-25 orbits during its lifetime. The orbital speed is 217 km/s, i.e. 1 light-year in ca. 1400 years, and 1 AU in 8 days.
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