6 June 2012: last Venus transit of our century

In the past, great importance was attributed to the transit of Venus for measuring the distance between Earth and the Sun (the Astronomical Unit), and therefore for our knowledge of the Solar System.

In the present age of  radar measures of the Sun-Earth distance with uncertainties of the order of few tens of meters, the importance of such phenomenon seems limited to its rare occurrence and spectacular aspects. In fact, the average alignment of Venus at the node line between the Sun and the Earth only occurs every century and a quarter.  The next transit will occur on 11^th September 2117.

The upcoming Venus transit of 6th June 2012 is much awaited by astrophysicists since it will allow them to collect some of the most important measures for improving present techniques for detecting exoplanets, i.e. planets orbiting stars other than the Sun. Venus transit observations are particularly important due to Venus’ great similarity to Earth.

In the near future, these techniques will enable investigation of the atmospheres of earth-size planets and thus possibly answer several questions among which is the answer to the question if we are really alone in the corner of the Universe.

Among the astrophysicists who are awaiting the phenomenon is Paolo Molaro of the Astronomical Observatory of Trieste of the National Institute for Astrophysics, who is Principal Investigator of the team availing of HARPS spectrometer installed at the ESO 3.6 meter telescope at La Silla in Cile, on the Andean Mountains.   Paolo Molaro and his colleagues, among them the Italian astrophysicist Lorenzo Monaco of ESO, will measure spectral lines of the Sun’s integrated light with the aim of confirming the “signature” of the transit of Venus.

However, the telescope will not be aimed at the Sun but at the Moon because measures will be performed on the light reflected by Earth’s satellite, since this is the only way to obtain an integrated solar spectrum, i.e. a spectrum of the whole disc of the Sun. Observations are aimed at measuring the distortion of the Sun’s velocity profile caused by the transit of Venus. According to Paolo Molaro:  “it is quite a small difference, of the order of one meter per second. Almost the movement of a person walking in the street,  but it is now or never, at least in this century”.

On the occasion of the Venus transit and to illustrate his observational programme, Paolo Molaro will give a public talk entitled “Venus transit: history and science” on Tuesday 5^th June at 5.00 pm in the seminar room of the Observatory’s seat of Villa Bazzoni, address: Via Bazzoni n. 1, Trieste.

The principal events occurring during the transit of Venus as viewed in Trieste area (click on the image for computer animation): the transit begins in the night of  6th June and therefore will be visible only at sunrise at 5.07 am.  At that time Venus will be visible on the final part of the transit, almost at egress from the solar disk. The transit viewed from Trieste will last slightly more than one hour and will end at 6.55 am, but this final phase of the transit  will not be easy to observe since at that time the Sun will be low on the horizon behind the Karst plateau.

Astronomical Observatories and Institutes located in the zone in which the entire transit is visible will transmit online all the phases of the  transit, among them are Hawaii’s Mauna Loa Observatory and NASA.

Further information on Venus Transit are available on the web page of  Venus Transit 2004 (by M. Messerotti).