Edwin Powell Hubble (1889-1953) was born in Marshfield, Missouri, nine years after a devastating F4 tornado destroyed most of the town, killing 99 people and injuring 100. The Hubble family moved to Wheaton, Illinois (near Chicago) the year Edwin was born.
After receiving a B.S. degree from the University of Chicago in 1910, Hubble spent three years at Oxford University as a Rhodes Scholar. The experience must have made quite an impression on young Hubble, as he returned to the U.S. with an affected British accent and other mannerisms (such as smoking a pipe) that stayed with him (and sometimes irritated others) for the rest of his life.
George Ellery Hale (1868-1938) offered Hubble a job at the Mount Wilson Observatory in 1919, and that same year also hired a talented man who would soon become Hubble’s assistant, Milton Humason (1891-1972), just as Mt. Wilson’s 100-inch Hooker telescope (the largest in the world at that time) started to see regular use.
Hubble identified Cepheid variables in M31, the Andromeda Nebula (and some other spiral nebulae), using the 100-inch in 1922-1923. From those observations, Hubble determined without a shadow of doubt that the Andromeda Nebula is in fact another galaxy of stars lying far beyond our own Milky Way galaxy. Up until this time, there was great debate about whether “spiral nebulae” like M31 were within our own galaxy or beyond it. Many thought that our galaxy was the entire universe. Thanks to Edwin Hubble and those who followed him, we now know that our galaxy is but one of many billions in this unimaginably vast universe we are lucky enough to explore.
How did Hubble use the faint Cepheid variables to determine the distance to M31? Cepheid variables are very luminous yellow giant and supergiant stars whose luminosity is directly related to the period of time it takes for the star to vary in brightness from brightest to dimmest to brightest again. The longer the period, the brighter the star really is. Knowing the apparent brightness of a star (dependent on distance), and knowing its true brightness (not dependent on distance), we can easily calculate the distance to the star. In the case of M31, the Andromeda Galaxy, we now know its distance to be 2.48 ± 0.04 million light years. M31 and the Milky Way are comparable in size and mass, and are by far the two largest galaxies of the Local Group, which contains at least 80 members. M31 and our Milky Way are moving towards each other due to gravitational attraction, and they will “collide” in about 4 to 5 billion years, probably leading to the formation of a giant elliptical or lenticular galaxy. But no one on Earth will witness this event. Due to the warming Sun, the surface of the Earth will become lifeless in a billion years or so.