Astronomers are planning to use NASA’s Hubble Space Telescope to observe next
month’s historic transit of Venus across the sun’s face. But there’s a twist. Astronomers can’t point Hubble anywhere near the sun, because our star’s bright light could damage the telescope’s super-sensitive instruments. So Hubble will watch the June 5-6 Venus transit by using the moon as a mirror. The goal is to see if Hubble can determine the makeup of Venus’ atmosphere by studying sunlight that has poured through it. Astronomers already know a great deal about Venus’ air, so next month’s observations are a test run to see if the technique could be used to determine the atmospheric composition of faraway alien planets. Astronomers hope the method can help them find an alien Earth, a habitable planet much like our own, orbiting a distant star. Venus is an excellent proxy for this search because it’s nearly the same size and mass as Earth. Hubble will be locked onto one location on the moon’s surface for the entire seven-hour transit, during which Venus will appear as a tiny black dot crossing the sun’s face. Astronomers need the long observation time because they’re looking for extremely faint spectral signatures. Accoridng to astronomers only 0.001 percent of the sun’s light will filter through Venus’s thick atmosphere and be reflected off the moon. The astronomers will use an arsenal of Hubble instruments, the Advanced Camera for Surveys, Wide Field Camera 3, and Space Telescope Imaging Spectrograph, to view the transit in a range of wavelengths, from ultraviolet to near-infrared light. During the transit, Hubble will snap images and perform spectroscopy, dividing the sunlight into its constituent colors, which could yield information about the makeup of Venus’s atmosphere. Next month’s Venus transit is a special event. The last Venus transit occurred in 2004, but the next one won’t happen until 2117.