Galileo used his telescope in 1609 to look at the hazy Milky Way in the sky andfound it to be composed of many stars. It was eventually understood that the Sunwas just one of the many stars in the Milky Way. But what were the size and shapeof this Milky Way galaxy? In 1750, a watchmaker in England, Wright, proposedthe so-called "grindstone model", in which the entire Milky Way is like a thickdisk-shape grindstone. This is pretty close to the real shape of the Milky Way.However, without the means to measure the distances between stars, these werejust conjectures lacking substantial proofs. The first scientific study of the size and shape of the Milky Way was done bythe discoverer of Uranus, Herschel, who tried to answer this question in 1784. Infact, he did not actually know the distances between stars, as the first distanceobservation was done using the parallax method not until 1838. Instead Herschelassumed that the distribution of stars was homogeneous, and that the stars’brightness was similar. Therefore, the number of stars in one direction would tellus the distance between the solar system to the edge of the Milky Way in thatparticular direction. He used this star-counting method to infer that the MilkyWay's shape is like a disc, about 15,000 light-years in diameter, 3,000 light-yearsthick, and centered around the solar system. For the next 100 years or so, althoughastronomers improved on Herschel’s observations, the results were almost thesame. It was just that the estimate of the size of the Milky Way increased graduallyto a diameter of about 30,000 light-years, and 6,000 light-years in thickness.