Research Astronomer John Butler created an exhibition, ``Measuring the Solar System'', timed to coincide with the 8 June 2004 Transit of Venus, the first such transit visible for 121.5 years (the last was on 6 December 1882). The exhibition presented drawings, images and artefacts held by the Armagh Observatory and elsewhere, concerning various previous transits of Venus which historically had provided the first direct measurements of the size of the solar system.
Transits of Venus usually occur in pairs separated by 8 years, each transit `season' (when Venus and the Earth happen to lie in an exact straight line with the Sun) currently beginning at alternating intervals of 105.5 and 121.5 years after the last event of the previous pair. (In fact, the key to understanding Venus transits is the 395/243 mean-motion commensurability with the Earth, which produces a nearly exact 243yr cycle of events.) Recent transits have occurred on 7 December 1631 and 4 December 1639; 6 June 1761 and 3 June 1769; and 9 December 1874 and 6 December 1882. The 8 June 2004 event will be followed by another on 6 June 2012; and then by another pair on 11 December 2117 and 8 December 2125.
The Armagh Observatory Transit of Venus exhibition was open to the public, Monday to Friday, during the two-week period 31 May to 11 June. Further details of the exhibition can be found on the Observatory web-site at http://star.arm.ac.uk/venustransit/exhibit/. In addition, staff made arrangements on the day of the transit to provide (i) a live web-cast of the transit, for projection in the Library and on the internet, using data from the 5-inch Meade ETX-125EC; (ii) observations of the transit by the `projection' technique with the newly restored Grubb 10-inch refractor; and (iii) further observations using a portable solarscope borrowed from the Armagh Planetarium and other instruments. Unfortunately, poor weather meant that only limited opportunities were available to observe the Sun properly during the transit, but conditions improved towards the end of the event and several people, including the Mayor of Armagh City and District Council, Councillor Mrs Pat O'Rawe MLA, were able to enjoy the final stages of the phenomenon and witness 3rd and 4th contacts.
Systems Manager Martin Murphy reported that despite the generally cloudy weather the Observatory web site for the transit generated so much interest that the internet connection was saturated at full capacity from about 08:00 until approximately 04:00 the following day. On the main web site (http://star.arm.ac.uk/) average daily `hits' for May, approximately 13,000, rose to almost 300,000 on June 8, and average Distinct e-Visitors (DeVs) rose from approximately 1,200 to 16,500 for the same period. Owing to caching by the large internet service providers (ISPs), this is very much a lower limit to the number of people who viewed the site.
The Director thanks the many staff who involved themselves in these arrangements and activities, especially John McFarland, Martin Murphy, David Asher, John Butler, Apostolos Christou, Michael Smith and PhD students Amir Ahmad, Natalie Behara, Ana M. García Suárez, Bebe Ishak, Miruna Popescu, Babulakshmanan Ramachandran, and Ignacio Ugarte Urra.