A rare transit of Mercury will take place tomorrow, the Astronomical Society said.

This will see the smallest planet in the solar system pass directly between the earth and the sun. The last time such an event was visible from Malta was in 2003, and the next time will be in 2019.

During the transit, Mercury will appear as a dark silhouetted disk against the bright surface of the Sun.

From Malta the transit will start to be seen at 1.12pm, when Mercury starts to enter the sun's disk. It will continue until the sun sets at 7.55pm.

The event is visible from parts of western Europe, the western part of north and west Africa, the eastern part of North America and most of South America.

People with access to a moderate-sized telescope should be able to see mercury as a dark disk on the sun, comparable in apparent size to a small sunspot, but somewhat darker.

The society warned that the blinding brilliance of the sun should never be viewed directly through optical instruments.

A safe observing method, it said, involved the projection of the sun's image with a telescope upon a piece of white cardboard which could be watched without harm to your eyes. This procedure has the advantage of allowing several persons to observe simultaneously with the same instrument.