For followers of Nostradamus, this is a chance to relish. What better time than the year 2000 -- prelude to the new millennium -- to predict all sorts of catastrophes driven by celestial objects? And the planets, jointly taunting the doomsayers, have chosen to dance together before their eyes.

Mars, Jupiter and Saturn clustered for the first time on April 6, within a circle 9 degrees wide. On April 14, they gathered again in a 5-degree circle. And last month's dance was just a prelude to this month's fiesta. On May 5, Mercury, Venus, the Moon and the Sun join in too, grouping in a circle of 26 degrees.

Illustration shows the planets as they align today. Photo: NASA

The Moon will soon part company, but the planets will continue to cluster till May 17, when Mercury, Venus, Mars, Jupiter and Saturn, plus the Sun, will be crammed within a 19 degrees 25 minutes circle. A crowded picture indeed. But even a doomsayer should know that such gatherings are not uncommon. In the last couple of thousand years, the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn have gathered within a 30-degree circle twenty-eight times, and today is the twenty-ninth.

All this with no dangerous consequences for the Earth, for the simple reason that nothing can happen. The Solar System is so wide and empty that the planets are like grains of sand scattered in space. The Sun and Moon induce tides on Earth, for the entertainment of sunbathers and windsurfers on the beaches. The tides vary as time passes, in ways well explained by the changing configuration of Sun and Moon.

Planets also cause tides on the Sun. In order of importance, Jupiter, Mercury, Venus and the Earth all exert tidal effects, which have not yet been measured.

The present alignment of the planets is a special event for those studying this effect. It will delight the scientific researchers who are interested in the influences of the planets on the Sun and, conversely, the influence of the Sun on the planets, including the Earth.

But that's all. Earthquakes? Other calamities and disasters? Pure fancy!

So what is this planetary grouping? When we look up at night, everything within our field of vision is projected onto the dome of the sky, the celestial sphere. And if two or more objects lie in almost the same direction, they will appear close together on the dome even if in reality they are they are at vastly different distances. A planetary grouping is therefore a perspective view of an alignment in space. Is that all? Yes.

Watch the planets with SOHO

An instrument on the U.S./European SOHO satellite sees three planets almost in line with the Sun itself, which is the white ring inside the mask that blocks its direct light. The horizontal streaks on the planets are instrumental effects. Photo: NASA/ESA

Last month was the only opportunity to see the planets gathering in line, with the naked eye. Now they are invisible because they are too close to the Sun in the sky. However, that is an advantage for the ESA-NASA SOHO spacecraft, which observes the sky in the Sun's vicinity with its coronagraph LASCO. Already Jupiter, Saturn and Mercury are in the field of view, as seen in the accompanying SOHO image.

During the coming days the planets change positions relative to the Sun, and on May 15 Venus will join them in the LASCO field of view. But then Mercury will move out of the picture, so the unprecedented sight of four planets near the Sun will not last long. It will be shown in a mid-May report, here on the ESA Science web site.

Meanwhile, anyone can watch the dance of the planets near the Sun, day by day, by visiting the SOHO web page of "Very latest images" and looking at the LASCO C3 image.

So don't panic, but enjoy the cosmic spectacle and consider the following test of your astronomical skills!

Cassini-Huygens is in the line too
Jean-Pierre Lebreton, ESA's project scientist for Huygens says: "If you had good enough eyes (I mean a very big telescope) you would be able to spot the Cassini/Huygens spacecraft as well, in the alignment of the planets!"

The NASA-ESA Cassini/Huygens spacecraft is bound for Saturn, where ESA's Huygens probe will land on Saturn's largest moon, Titan. At present Cassini/Huygens is on its way towards Jupiter, having exited the Asteroid Belt last month. Let's do a little exercise. Cassini/Huygens was observed from the Earth with a modest telescope a few days after launch in October 1997, and also in August 1999 after the Earth flyby.