Transit of Mercury, 7 May 2003
On the morning of 7 May 2003, astronomers, students and members of the public observed a transit of Mercury from the Royal Observatory, Greenwich (ROG).
In the past they were of great interest to astronomers and were used to measure the scale of the solar system. Although occuring more recently, transits of Venus are rarer still – the last was in 1882 and the next was observed in June 2004. See more on 2004 transit of Venus.
Transits occur when either Mercury or Venus move directly between the Earth and the Sun. Each planet is then seen in silhouette as a black disk in front of the Sun’s surface in a phenomenon rather like an interplanetary solar eclipse. Transits of Mercury are quite rare – on average 13 take place each century – and can only be observed safely with telescopes fitted with purpose-made filters.
The transit begins when the leading side of Mercury appears to touch the edge of the Sun’s disk at 06.11 BST. Shortly afterwards the Sun will have a small notch on its limb, which grows larger until 06.15 BST, when Mercury’s trailing edge passes in front of the solar disk. Mercury takes a long time to cross the Sun with the middle of the transit at 07.52 BST. At 11.28 BST the leading edge reaches the other side of the Sun and the transit ends when the trailing edge appears to touch the Sun's limb at 11.33 BST.
Throughout the event, telescopes with special protective filters will be trained on the Sun under the supervision of ROG astronomers.
Warning: Looking directly at the Sun with a normal telescope is extremely dangerous and can lead to permanent eye damage or even blindness. Never attempt to do this without full-aperture solar filters in perfect condition purchased from reputable astronomical suppliers.
