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The last transit of Venus that you or I have been able to see..

The last transit of Venus in our lifetime, which took place on June 5th 2012. Surely not many of you could see it because the visibility was not too good. The most fortunate were the people of the north-eastern Oceania and Asia region, and of course in the Arctic Circle. Some of you perhaps saw it in June 2004. If not, I’m afraid you’re running out of life chances, as the next event will be late 2117, and since you’re reading these lines (then you’re at least the age of knowing how to read) the probability that you’ll live to that date is quite small.

To explain the magic of the event is but a simple geometric coincidence without major transcendence. It is but a small “eclipse” of the Sun, but instead of it being the Moon that causes the eclipse, in this case it is the tiny planet of Venus.

We must take advantage of every “rare” event to get the most juice possible. The most obvious application, which has been used since the eighteenth century is to use transits to measure the distance between the Sun and Earth (distance known as Astronomical Unit ), using trigonometry, or more precisely by measures of parallax . The first accurate determinations were made by Joseph La Lande which measured a distance of 153 ± 1 million km. A century later, Newcomb got the value of 149.59 ± 0.31 million km, which at the time was amazing accuracy.

The value currently considered (measured with radar and telemetry techniques from space probes) is known with a precision of a few meters. I want to highlight an educational initiative of ESO who used this technique during the transit of Venus in 2004, for thousands of schoolchildren and observers worldwide could combine their observations and thus regain the value of the Astronomical Unit. All the measures of the more than 1500 participants were combined to determine with GPS the moments in which the different phases of the transit happened. The value finally obtained was 149.6 ± 11.8 million km.

Other more “modern” applications for this last transit of 2012 are indirectly related to the search for extrasolar planets . It has attempted to determine the variation pattern of overall brightness of the sun during this mini-eclipse (which unlike 2004 the Sun happens being in an active period magnetically speaking), to try to learn how to apply it to detect planets in other Similar stars. Also study the atmosphere of Venus can serve both to better understand the meteorology of the planet, to have a reference of the atmospheres we might expect to see on extrasolar planets, in this case uninhabitable.

An example is the animation of the right where it is to study the twilight phenomenon or “twilight” that clearly is seen in the bottom of the disc of Venus, as the Sun passes behind. More information on the project page .

Finally, I leave here with a photo. (credit: JAXA, NASA), the transit of 2012 was taken with the instrument SOT on board the satellite HINODE .

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