According to the Space Telescope Science Institute (STScI), the NASA Hubble Space Telescope will use the moon as a mirror in order to detect minor dips in brightness during Venus' transit past the sun, the institute said in a statement. Astronomers have said that Venus transits occur in pairs, separated by eight years. The next sighting is due to occur in June 5-6, and the one after believed to be in 2117. Due to the infrequency of the event the Director of STScI, Matt Mountain, has decided to undertake this project in order to learn how to detect atmospheres of earth-sized planets. The telescope will measure minute changes in light being reflected off the moon as Venus passes between the moon and the Sun. “We don't know if it will work, but it's worth a shot,” Mountain said in an interview with the Maryland Morning. “If it does work, we'll get an idea of what earth-size would look like … It will guide us in the future if we ever see dip like it; we're seeing a very small planet … It's quite a risky project, but the payoff would be quite remarkable, for we'd actually be able to measure the atmosphere of Venus using the Hubble Space Telescope.” The observation will be extremely delicate, as scientists must analyze over seven hours of data from the lunar readings, searching for faint spectral signatures. The Hubble orbits the earth in 96 minutes, 40 of which has the Earth occulting Hubble's view of the moon. Only 1/100,000th of the sunlight will filter through Venus's atmosphere and be reflected off the moon and with only one shot to have such an opportunity to study Venus, the astronomers must carefully plan how the study is to be carried out. In preparation for the event, astronomers have turned the Hubble towards Tycho, a prominent impact crater on the lunar surface. The picture taken and released by NASA using Hubble's Advanced Camera for Surveys, reveals lunar features as small as roughly 170 meters across. The large cavity near the top of the picture is the impact crater, caused by an asteroid strike about 100 million years ago. The bright trails radiating from the crater were formed by material ejected from the impact area during the asteroid collision. Tycho is about 80 kilometers wide and is circled by a rim of material rising almost 5 kilometers above the crater floor. The image measures 700 kilometers across, an area slightly larger than that of New Mexico.
