Messier 100 is a spiral galaxy in the constellation Coma Berenices, about 55 million light-years from Earth. Messier 100 is a starburst galaxy, with star formation prominent near the centre of the galaxy in two tightly wound spiral arms. The looser, outer spiral arms also contain star forming regions with clusters of young, hot, blue stars. The galaxy contains around 400 billion stars and has a radius of 53,500 light-years. Charles Messier, the 18th century French astronomer, catalogued over 100 galaxies and clusters. Through the telescopes available at the time, comets, nebulae, globular clusters and galaxies appeared just as faint, diffuse blobs. The image is from the NASA/ESA Hubble Space Telescope's Wide Field Camera 3.