Figure 15-2 RIVUXG High-Tech Telescope of the Mid-Nineteenth Century (a) Built in 1845, this structure housed a 1.8-m-diameter telescope, the largest of its day. The improved resolution it provided over other telescopes was similar to the improvement that the Hubble Space Telescope provided over Earthbound optical instruments when it was launched. The telescope, as shown here, was restored to its original state in 1996–1998. (b) Using his telescope, Lord Rosse made this sketch of the spiral structure of the galaxy M51 and its companion galaxy NGC 5195. (c) A modern photograph of M51 (also called NGC 5194) and NGC 5195. The spiral galaxy M51 in the constellation of Canes Venatici is known as the Whirlpool Galaxy because of its distinctive appearance. The two galaxies are about 20 million ly from Earth.