If they look into the sky one night next week, they may see... a red Moon.

Blazing across the heavens will be two fiery stars -- the first comets of the Millennium that are expected to be visible by the naked eye.

Then, in June, Earth, Venus and the Sun will all be directly aligned, staging a cosmic eclipse that no human alive today has seen.

Not for nothing have keen astronomers around the world pencilled this as the time to take their annual vacation and place nightly orders of pizza in order to devote their fullest gaze to the skies.

The show kicks off on Tuesday May 4 with a total lunar eclipse, which occurs when the Moon, the Sun and Earth are all in alignment.

The Moon will slide into the cone of shadow of the Earth cast by the Sun but it will not become invisible, for it will be tinged by residual sunlight that is deflected by Earth's atmosphere.

As most of this light is in the red part of the spectrum, the Moon often turns coppery, orange or even brown.

"The eclipse will be widely visible from Europe, Africa, Asia and Australia," says NASA expert Fred Espenak.

"North America will miss the entire event, but most of South America will witness the last stages of the eclipse which will already be in progress at moonrise. Similarly, the Moon sets in eastern Asia and Australia during various stages of the eclipse."

In easterly time zones, the date will be May 5 (total eclipse is from 1952 to 2108 GMT on May 4).

Total lunar eclipses usually occur every couple of years. But planetary dynamics mean that we are right in a splurge of them: there were two in 2003 and there will be a fourth on October 28.

In the meanwhile, two major comets, both of them spotted only within the last few years, will be sliding into position for good viewing from Earth as they race past us on their elliptical track around the Sun.

They are C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR), whose strange names are derived from their discoverers -- two US robot telescopes that scour the heavens for space rocks.

Comets have long been considered the harbingers of great events, of famine, earthquakes, war, the death and birth of kings.

Astrophysicists find them just as fascinating, as the primitive material of frozen gas, dust and rock left from the building of the Solar System some 4.6 billion years ago.

The last comet to be visible to the naked eye from Earth was Hale-Bopp, which put on a spectacular in 1997.

"Predicting the brightness of 'new' comets -- those freshly arrived from the outermost reaches of the Solar System, like these -- is fraught with risk," says the US magazine Sky & Telescope.

"With a little luck, one or both could become distinctly visible to the naked eye. Or they could remain targets only for binocular users who know just where to look."

Comet NEAT will be at its closest on May 6, coming within 48,020,000 kilometers (30,013,000 miles) of Earth, while LINEAR's nearest approach will be on May 19, at 39,790,000 kms (24,870,000 miles).

These are the preludes for June 8, when Venus, the Solar System's second planet, will be directly aligned between Earth and Sun.

Venus will be visible as a tiny black dot crawling over the face of the Sun -- and for that reason, proper eye protection is an absolute must.

"This 'Venus Transmit' happened last time in 1882," says Richard West of the European Southern Observatory (ESO).

"It now provides a vast public in Europe, Africa, Asia and Australia the opportunity for a unique experience."

ri/bm

+ Websites: (http://sunearth.gsfc.nasa.gov/eclipse/lunar.html); (http://skyandtelescope.com); (http://space.com); (http://www.vt-2004.org)

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