May 5, 2012
Hubble To Use Moon As Mirror To Observe Venus Transit
NASA officials have announced plans to use the moon like a mirror in order to allow them to see the forthcoming transit of Venus across the face of the sun on June 5 and 6, the U.S. space agency announced in a Friday press release.
The seemingly unorthodox technique is necessary because the Hubble Space Telescope, which will be used to observe the transit, cannot look at the sun directly. To work around that issue, astronomers will be pointing the telescope at our planet's satellite, using it to capture reflected sunlight and allowing them to isolate the minute fraction of the light which passes through Venus's atmosphere.
"These observations will mimic a technique that is already being used to sample the atmospheres of giant planets outside our solar system passing in front of their stars," NASA said in a statement posted to the Hubble mission page. "In the case of the Venus transit observations, astronomers already know the chemical makeup of Venus's atmosphere, and that it does not show signs of life on the planet. But the Venus transit will be used to test whether this technique will have a chance of detecting the very faint fingerprints of an Earth-like planet, even one that might be habitable for life, outside our solar system that similarly transits its own star.
"Venus is an excellent proxy because it is similar in size and mass to our planet," they added, noting that the astronomers would use a variety of different Hubble instruments in order to view the transit in a wide range of wavelengths, ranging from ultraviolet to near-infrared light. During the event, the space telescope will be taking pictures and performing spectroscopy in order to provide additional information about the planet's atmosphere.
In preparation for that event, NASA on Friday released a photograph of the lunar impact crater Tycho, which they refer to as one of "the most violent-looking places on our moon." The image was taken with the Hubble's Advanced Camera for Surveys and was part of the space administration's preparation for the upcoming transit.
"Hubble will observe the moon for seven hours, before, during, and after the transit so the astronomers can compare the data. Astronomers need the long observation because they are looking for extremely faint spectral signatures. Only 1/100,000th of the sunlight will filter through Venus's atmosphere and be reflected off the moon," NASA officials explained.
"Because the astronomers only have one shot at observing the transit, they had to carefully plan how the study would be carried out. Part of their planning included the test observations of the moon, made on Jan. 11, 2012," which included the image captured of the Tycho crater, they added. "Hubble will need to be locked onto the same location on the moon for more than seven hours, the transit's duration. For roughly 40 minutes of each 96-minute orbit of Hubble around the Earth, the Earth occults Hubble's view of the moon. So, during the test observations, the astronomers wanted to make sure they could point Hubble to precisely the same target area."
According to NASA, this will be the last time this century that Venus will pass in from of the sun, and the next time the phenomenon will occur will be in the year 2117. The transit, which usually happens twice in a span separated by eight years, last occurred in 2004, they added.
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