EDWIN P. HUBBLE
Cosmological Revolutionary
Most people know of Edwin P. Hubble because of the space observatory that bears his name. The Hubble Space Telescope is one of the great workhorses of astronomy and has shown astronomers fascinating objects and processes throughout the universe. Its name honors one of the astronomical stalwarts of the early twentieth century.
What did a former lawyer from Marshfield, Missouri, do to get his name on a telescope? He proved that some distant clouds of light in the sky are actually distant galaxies that lie well beyond the boundaries of our own home galaxy, the Milky Way. In a very real sense, his work presaged the great work of the telescope that bears his name.
From Law to Astronomy
Edwin P. Hubble was born in 1889, the son of an insurance executive. He was interested in science as a child, studied mathematics and astronomy in college, and at his father’s urging, studied law at Oxford University in England. When he turned twenty-five, Hubble decided to make a profession of astronomy and attended the University of Chicago, earning his PhD in 1917. His major interest was the study of so-called faint nebulae. After serving in the army in World War I, Hubble joined the staff of Mount Wilson Observatory in California, where he used the newly finished 100-inch Hooker telescope to study these objects in more detail.
Hubble’s Major Accomplishments
Edwin Hubble put his access to one of the world’s best telescopes to good use. While studying the Andromeda Spiral Nebula (today known as a spiral galaxy) in 1923, he discovered the flicker of a Cepheid variable star. These are used as “standard candles” in determining distances in the universe. His discovery answered a question: whether or not these spiral nebulae were inside our own galaxy or whether they lay much farther away. Using his measurements of Cepheids, Hubble was able to show that they were very distant and definitely not part of our own galaxy. Up until that time, many astronomers held the view that the Milky Way was the entire cosmos. Hubble’s discovery showed, for the first time, that the universe was much larger than anyone thought. It was a revolutionary finding. Astronomers continue to use Cepheid variables as one part of a cosmic distance toolkit to determine how far away objects are and how fast they are moving. This remains one of Hubble’s greatest contributions to astronomy.
Hubble also discovered that objects in the universe seem to be moving apart, thus showing that the universe is expanding. He determined that the velocity of this so-called “recession” is faster the farther away an object lies from us. This idea of an expanding universe rocked astronomy and is one of the principal foundations of the science of cosmology. Others had suggested that the universe might be expanding; Hubble went to work to calculate a rate of expansion based on his observations. That expansion rate came to be called the Hubble Constant, often noted in astronomy literature as Ho (pronounced “H-naught”). Hubble originally calculated it to be about 500 kilometers per second per megaparsec. Today, with more sensitive telescopes and techniques, the value of Ho has been adjusted to 67.15 ± 1.2 kilometers per second per megaparsec.
Edwin Hubble observed many galaxies in his career, and he set to work classifying these objects by their shapes. His Hubble sequence of galaxy morphologies is the basis for classifications still used today. Galaxies can be spiral, elliptical, lenticular, or irregular. In modern astronomy, the classifications of spirals in particular are subdivided into spirals with tightly wound arms and big central bulges, spirals not so tightly wound and having fainter bulges, and loosely wound galaxies with very faint central regions. Lenticulars have bright central regions but no spiral arms and look similar to the elliptical galaxies (which also have no spiral arms). Irregulars are just that—blob-shaped galaxies with no spiral arms, but often showing brilliant regions of star formation. The Large and Small Magellanic Clouds are good examples of irregulars.
Edwin P. Hubble continued his work at Mount Wilson until his death in 1953. His work revolutionized astronomy and cosmology, and it’s no wonder that the Hubble Space Telescope is named for his life and accomplishments.