Wednesday, October 15, 2014

From the Peruvian Andes to galaxies and the Big Bang

A century ago our universe was just a little village called the Milky Way. Today, we know that there are billions of galaxies in the cosmos, and that the universe is expanding due to the Big Bang. The Peruvian Andes played a fundamental role in those discoveries.

Less than a century ago, Edwin Hubble showed that certain "nebulae" are actually galaxies like our Milky Way, by using the so-called period-luminosity relationship of variable stars known as cepheids, that allowed him to estimate distances. Using cepheids located in the Andromeda "nebula", Hubble concluded in the 1920s that Andromeda is far outside our Galaxy. Later, Hubble found that the most distant galaxies have the largest velocities away from Earth. This means that the Universe is expanding, and that everything started in the Big Bang.

Andromeda "nebula". (c) NASA.
Hubble relied on the period-luminosity relationship of cepheids to estimate how far away are distant galaxies. This relationship was discovered by American astronomer Henrietta Leavitt, using observations taken in the Peruvian Andes, more exactly from the Boyden Station in Arequipa. The Harvard College Observatory built that observatory in the 1890s and early 1900s, to have access to the Souther Sky. Henrietta Leavitt measured the brightness of variable stars in the Magellanic Clouds, and discovered the period-luminosity relationship followed by cepheid variables.

Thus, observations from the Peruvian Andes were key to set the standard ruler to measure large distances, leading to the birth of Extragalactic Astronomy and Cosmology. In another post I'll describe how observations gathered in Harvard's observatory in Arequipa led to the birth of Stellar Astrophysics.

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