Astrophysical Classics: Measuring the Age of the Earth

Astrophysical Classics: Measuring the Age of the Earth

It took homo sapiens hundreds of thousands of years on the planet to understand a fundamental, simple-sounding, question: how old is the Earth? The answer to this question has gone down in the history books as one of the most important geophysical and astrophysical discoveries of the past century. This paper, by Clair Patterson in 1956, is credited with providing the first accurate, measured age of the Earth.

Venus as a (non-habitable) Exoplanet

Venus transits the Sun, from the frame of the Earth, about twice every century, separated by eight years. The last one happened in 2004, and another is happening in June 2012. Observing the transmission spectrum during the 2012 transit—and comparing it to measured transmission spectra of the Earth, taken during lunar eclipses—will tell us how hard it will be to distinguish two planets that look identical in mass and radius, but have extremely different atmospheric properties.