Transits of Venus in 2004 and 2012
Transits of Venus are a rare occurrence and take place within 1º 45’ of the nodes. Because five synodic revolutions of Venus take 8 years, they commonly occur eight years apart at one node. This node will again be favourably placed some 240 years later and near the halfway point a pair of transits is likely to occur at the other node. Transits of Venus have occurred in 1761 and 1769 (seen by Captain Cook from Tahiti), 1874 and 1882. The next pair of transits will occur in 2004 and 2012 and after that 2117 and 2125.
Compared with transits of the inner planet Mercury, the transits of Venus will be quite spectacular. Mercury had an apparent diameter of 10" at its last (grazing) transit seen from Australia on 16 November 1999. Venus will have a diameter of 58" for both 2004 and 2012 transits and thus the disc will have nearly 35 times the surface area of Mercury on that previous occasion. (The apparent diameter of the solar disc will be 1891" for both transits.) The photograph below has a simulated disc of Venus to a similar scale and resolution superimposed upon the image of the Mercury photograph taken at the 1999 transit.
(For the skeptics, nothing in this photo is quite what it appears. The original photo was taken of a piece of white paper on which the image of the transit of Mercury was projected. The print of this photograph was scanned, the contrast increased, and the image was then sharpened a little electronically in the photo processing. Then a yellow colouration was added to make the sun appear more 'lifelike'. Finally Venus was added electronically as a blob of the appropriate size and the colour of the sky background with a slightly soft outline for realism. Though I certainly intend to carefully observe and photograph the event and its attendant phenomena - see following - this is one event that would be exceedingly easy to fake providing you started with a photograph of the sun at the appropriate resolution.)
I have checked Jean Meeus’ tables, David Herald’s ‘Occult’ computer program, and ‘Starry Night’ planetarium program. I have given preference to the Herald program which lists Australian sites, and have arrived at the following scenario for these transits:
8th June 2004
This transit will cross the southern part of the solar disc from position angle 115º to 215º.
The first contact (exterior of the disc of Venus) will occur around 3.07 pm Eastern Australian time (5hrs 07min UT) when in the Brisbane area, the sun is at 20 degrees altitude.
Second contact, when the disc of Venus is wholly within the sun occurs around 3.26pm (5hrs 26min UT) when the sun has sunk to 17 degrees altitude. (Meeus' geocentric tables has first and second contact occurring 10 minutes later). Venus then continues crossing the solar disc and local sunset prevents further observation at 5.00pm. The transit continues and mid point is reached after 8hrs UT with third contact a little after 11hrsUT and fourth contact twenty minutes later. The transit will last 6hrs 12minutes.
6th June 2012
This transit crosses the northern part of the solar disc from position angles 40º to 291º.
The whole of this transit will be visible from Eastern Australia. As an example, from Brisbane, first contact will occur around 8.15am (22hrs 15minUT on the 5th) with the sun 19 degrees in altitude, second contact at 8.34am (22º alt), the centre of the transit at 11.30am (1hr 30min UT on the 6th) (40º alt), third contact around 2.26pm (27º alt) and fourth contact around 2.44pm (25º alt). Meeus’ geocentric figures for the beginning of this transit correspond closely but by the end are 11minutes late. The transit will last 6hours 40 minutes.
For interest the next following transit on December 11th 2117 is central at around 12.50pm Eastern Australian Time and it again favours Eastern Australia, though summer weather can sometimes be capricious. However perhaps this is just of academic interest for the reader...
As in the case of transits of Mercury, the 'back drop' effect also occurs for Transits of Venus. However it is much more apparent due to the additional factor of Venus' thick atmosphere. Perhaps as early as before the commencement of the transit, a bright ring will be seen outlining the planet. Certainly this effect should at least be able to be observed between the first and second contacts on the section of the planet that is not projected against the sun. Then on second contact (and again before third contact), there will not be a clean break or merger with the solar limb, but rather a black 'teardrop' effect will be seen joining the planet and limb, and when it disappears the two will be well separated. The thick atmosphere also tends to give the planet a slightly fuzzy outline. Careful timings (if possible) of all four contacts are also valuable, and you will need to record your longitude and latitude when reporting them.
CAUTION: It is stressed that appropriate precautions be taken when attempting any solar observations. A mishap or carelessness may cause permanent damage to sight.
Finally…The following are three frames from a 'powerpoint' presentation simulating the 8 June 2004 event as seen from South East Queensland:
