extending beyond the stellar disk is a much thicker disk of gas. recent observations indicate that the gaseous disk of the milky way has a thickness of around 12000 light years–twice the previously accepted value. as a guide to the relative physical scale of the milky way, if the solar system out to the orbit of pluto were reduced to the size of a us quarter (about an inch or 25 mm in diameter), the milky way would have a diameter of 2,000 kilometers. at 220 kilometers per second it takes the solar system about 240 million years to complete one orbit of the galaxy (a galactic year).