In this exercise we measure the period and apparent magnitudes of Cepheid variables in the galaxy M100 on FITS images with the free European Hands-On Universe software SalsaJ. The absolute magnitude is derived using the Period-Luminosity relation and the distance to M100 can then be determined using the distance relation. Finally we calculate a value for the Hubble constant (using a value for the recession velocity of M100 observed by other scientists) and estimate the age of the Universe. English Version. LASER PRINT. Full-colour.