A clear sky on Wednesday evening will give people in Malta the opportunity to witness the first total eclipse of the moon visible from the Maltese Islands for over three years, the Astronomical Society said.

"This time round we will be favourably positioned to get a unique view from the first partial phase to the end of the eclipse."

The society said it was holding a public observing session at Żonqor Point, Marsascala, starting at 9 p.m.

The eclipse begins at 7:25 p.m. when the moon would still be below the eastern horizon. It would then be entering the earth's faint shadow called the penumbra, which is often difficult to detect in its early stages.

"Only as the moon slides deeper into the penumbral shadow would a keen-eyed observer see a subtle shading of the lunar surface.

"The moon rises at Malta just prior to it entering the earth's dark umbral shadow, an event which is expected to occur at 8:23 p.m.

"Even though the moon will be low in the twilit sky, one should notice its lower limb (eastern edge) getting dark. An unobstructed view toward the east will be a necessity," the society said.

It said that totality begins at 9:22 p.m. as the earth's shadow completely envelopes the moon. Totality will be at its midpoint at 10:14 p.m., and will end at 11:03 p.m.

How the moon will appear during totality is not known. Some eclipses are such a dark grey-black that the moon nearly vanishes from view. During other eclipses it can glow a bright orange.

The reason the moon can be seen at all when totally eclipsed is that sunlight is scattered and refracted around the edge of the earth by the atmosphere.

Global weather conditions and the amount of dust suspended in the air effect the transparency of the atmosphere.

A clear atmosphere on earth means a bright lunar eclipse. If a major volcanic eruption has injected particles into the stratosphere, the eclipse is very dark, the society said.

It noted that because of last year's eruptions of the Eyjafjallajökull volcano in Iceland and the Merapi volcano in Indonesia, clouds of ash and dust might still be floating high above the earth. As a result, the moon may appear darker than usual during this eclipse.

As the earth, moon and sun move out of alignment, sunlight will again illuminate the lunar surface.

For an hour after the end of totality the earth's dark umbral shadow will gradually uncover the moon. This phase ends at 0:02 a.m. on Thursday.

Until 1:01 a.m. the earth's light penumbral shadow will progress over the lunar surface until it leaves it.