– In April 1845, the world’s largest telescope pointed toward the M51 nebula, a fuzzy patch of light near the Big Dipper.Peering through the telescope was astronomer Lord Rosse. He was the first one to see the nebula’s spiral shape.
This telescope was the first to show that this bright spiral nebula was not a cloud of gas, but a constellation of stars. Examining photographic negatives of the Great Spiral taken on different nights, Edwin Hubble made a great discovery. He found that the nebula contains dozens of stars whose brightness fluctuates.
Astronomers knew how to calculate the distance to this special type of star.By determining the distance to the stars, Hubble found the distance to the spiral. Hubble discovered that the Great Spiral lay far beyond our Milky Way.it was an immense “island universe” of stars, millions of light-years away: another galaxy.