Henrietta Leavitt is considered one of the most important contributors to the field of astronomy. She discovered that variable stars with greater luminosity had longer periods. Leavitt was left in charge to identify variable stars in the Small Magellanic Cloud. She realized that the stars she had observed were indeed variable stars – named Cepheid Variables – because their brightness changed in a pattern. Like variable stars, the Cepheid Variables dimmed and brightened in regular periods.
However, Leavitt began to notice the relation between the brightness of a star and its’ period. A brighter star would exhibit a longer period for it to be at maximum brightness, dim down to minimum brightness, and brighten back to maximum brightness again. Leavitt graphed out the relation, showing that the brightness of a star and its’ period followed a straight line. This discovery is known as the “period-luminosity relationship.”
In addition, to account for the idea that a star may appear fainter because it is further away, Leavitt stated that because all the Cepheid variables were in the Small Magellanic Cloud, it can be assumed that they are all nearly at the same distance from Earth. Therefore, a Cepheid Variable’s apparent brightness
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One astronomer, Edwin Hubble, found a variable star located inside Andromeda’s spiral nebula and measured its’ period. By using Leavitt’s period-luminosity relationship, Hubble found the luminosity of that variable star. By knowing the star’s luminosity and measuring its’ apparent brightness, Hubble was able to calculate the distance from Earth to Andromeda. He calculated a distance of over 900,000 light years, which exceeded the distance across the Milky Way (100,000 light years). His findings proved that Andromeda was a galaxy in its’ own right, and therefore it is possible that there are other galaxies out in the