Though not as spectacular as transits of Venus, those of Mercury are much more common. I observed my first transit in 1960 and since then we have had transits in 1970, 1973, 1986, 1993,1999, and 2003. The next transit occurs on November 8^th 2006. The following transit of Mercury then does not occur until May 9^th 2016 (Universal Time), and this occurs at the wrong time to be visible from Australia.

These transits occur when inferior conjunction takes place near the nodes of the orbit and occur in May (descending node) and November (ascending node).

Principally because of elliptic nature of its orbit, the size of Mercury can vary considerably. It was 10" in diameter at its grazing transit on November 15^th 1999 (see below), 12" in diameter for the May 2003 transit, and once again will be10" for the November 2006 event. The diameter of the solar disc was 1902" in May 2003 and will be1937" for the November 2006 event. A report and photographs of the May 7^th 2003 transit appears on this site under 'Observations' and is available as a 'Powerpoint' upon application.

This transit travels in a north-westerly direction entering the south-eastern part of the disc at position angle 141º and leaving it on the western limb at position angle 269º. First contact occurs at 5.12amEAST (not daylight saving time) (19hrs 12min UT) for Brisbane with the sun only 4º altitude (having risen at 4.52am) and second contact occurs at 5.14am. Because of the low altitude these would be very difficult to observe from Eastern Australia. Mid transit occurs at 7.41amEAST (36º altitude in Brisbane) and third and fourth contacts respectively at 10.08am and 10.10am when the sun is 68º degrees altitude in Brisbane. The total length of the transit is 4hours 58 minutes.

An interesting phenomena for transits of both Mercury and Venus is the 'black drop' effect caused by atmospherics or optically. This occurs immediately after second contact or immediately before third contact. Instead of joining or separating cleanly with the solar limb a tear shaped drop effect is briefly observed connecting the planet and solar limb. It is worth watching for. Careful timings 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.