This paper considers the possibility that Earth could suffer a runaway or moist greenhouse effect, which probably turned Venus into a hellish wasteland long ago.
Tuesday was was the second of this century’s pair of transits of Venus; I didn’t catch the 2004 transit, but I was fortunate to have a prime view of Tuesday’s. Like many others, I turned my eyes (safely behind sun filters) towards the Sun and the little black dot traversing its surface. I asked the Astrobites authors to share their experiences with us.
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.