Hubble was able to measure the distances to only a handful of other galaxies, but he realised that as a rough guide he could take their apparent brightness as an indication of their distance.
Hubble ay upang masukat ang distances na lamang ng isang dakot ng iba pang galaxies, ngunit siya realised na bilang isang magaspang gabay na siya ay maaaring umabot ng kanilang mga maliwanag liwanag bilang isang indikasyon ng kanilang distance.