Don't miss the transit of Venus - you'll have to wait until 2117 for the next one!
Astronomers and space-gazers worldwide will be getting up extra early on Wednesday 6 June to make sure they catch the final transit of Venus of the 21st century.
The transit, which occurs when Venus passes directly between the Earth and the Sun, was last recorded in 2004. There won't be another one until the year 2117, with not many of us likely to be able to witness it then.
This transit only takes place on the rare occasions when the Sun, Venus and Earth are almost exactly in line; on average, it only happens every 80 years. Before the last transit, on 8 June 2004, no living person had seen a transit of Venus - the previous one was on 6 December 1882.
Transits occur in a 'pair of pairs' pattern that repeats itself every 243 years. First, two transits take place in December (around the 8th), 8 years apart. There follows a wait of 121 years and 6 months, after which 2 June transits occur (around the 7th), again 8 years apart. Then after 105 years and 6 months, the pattern repeats itself.
The 6 June transit will start at approximately 00:04 Central European Time (CET). It will then take about 20 minutes from the point when Venus first bears upon the disk of the Sun, the first contact, until the planet is fully silhouetted, the second contact. The planet will then take a curved path across the northern part of the Sun, and the mid-point of the transit will occur at around 03:30 CET. Venus begins to leave the Sun, the third contact, at about 06:37 CET, and the transit will be over, the fourth contact, at 06:55 CET.
The best parts of the world to watch the transit, predicted to last 7 hours in total, will be eastern Asia and Australasia, the Pacific Ocean and the north-western parts of North America. In Europe we will only be able to witness the later stages.
During the transit, Venus will be visible in silhouette as a dark disc set against the bright solar surface or photosphere. The planet is about 1/32nd of the diameter of the Sun, so it will block about 0.1% of the Sun's light from reaching the Earth.
To safely watch the transit, experts from the Royal Astronomical Society (RAS) advise using special eclipse-viewing glasses, so long as long as they are undamaged and observing is limited to a few minutes at a time. They also advise that eclipse glasses marked CE under the EU Directive on the safety of Personal Protective Equipment are preferable, as they are certified to conform to an agreed and effective safety standard. It is also useful to note that the capacity of eclipse glasses to block harmful radiations from the sun reduces with time, so any old glasses bought for watching previous eclipses should not be recycled, as their eye protection effectiveness cannot be guaranteed.
For researchers, the transit of Venus also presents two exciting opportunities.
Firstly, it is a chance to use Venus as an example of a transiting exoplanet, as astronomers will use the transit to test the techniques they have developed to analyse the composition, structure and dynamics of exoplanetary atmospheres.
Secondly, it allows simultaneous Earth- and space-based observations of Venus's atmosphere and offers new insights into the complex middle layer of Venus's atmosphere, a key to understanding the climatology of our sister planet.
An EU-funded research infrastructure (RI) project that has been supporting this work is EUROPLANET ('European planetology network'), which has received EUR 6 million of funding under the 'Capacities' Theme of the EU's Seventh Framework Programme (FP7). The project brings together 27 partner institutions from 16 European countries,
Dr Thomas Widemann of the Observatoire de Paris, one of the partner institutions, describes the transit of Venus as 'a unique opportunity to closely observe an Earth-like planet passing in front of a Sun-like star'.
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