Have you seen a transit of planet Venus? Chances are that you have not, since the last one took place in 1882. The next transit, which is a passage of a planet in front of the Sun, is due on Tuesday 8 June 2004 and is a sight not to be missed, because our island is very well placed to see the whole event from beginning to end.

From our Earth-bound vantage point, only transits of Mercury and Venus are possible. From the point of view of the outer planets, transits of the Earth (and any other planet nearer the Sun than them) may occur. On 11 May 1984, the Earth was in transit of the Sun for observers on Mars. The Earth took about 8 hours to go across the face of the Sun with the Moon about 6 hours behind, so that for a while both bodies would have been seen as black dots crossing the Sun ? had you been on Mars then.

Transits of Mercury are much more common than transits of Venus, with up to 13 Mercury crossings taking place on average per century. The last transits of Mercury seen from Mauritius were in 1993 and 2003. If you missed the opportunity of seeing the last transit of Mercury which took place on 7 May 2003, you will not have an opportunity to see one again in Mauritius until 13 November 2032. Do not worry: it will not be like waiting for Godot. Transits are rare events and those of Venus are even rarer. The last ones took place in 1874 and 1882, and the next are due in 2004, 2012, 2117 and 2125. The orbital characteristics of planet Earth and Venus are such that transits of Venus occur in pairs. The two transits within one pair are 8 years apart, and the pairs themselves occur with more than a century between them. Regarding the present pair, the 2004 event is favourable for Mauritius, while only the end of the 2012 show is to be seen from our local position.

It was Jonannes Kepler who, in 1629, was the first to predict the existence of transits, further to his discovery of the three laws of planetary motion which bear his name now. The great German mathematician and astronomer, however, did not see any in his lifetime as he died soon after in 1630, with a transit of Venus occurring just afterwards in 1631, seen by no one at all as it was not visible from Europe. The transit of Venus of 1639 became the first one ever to be witnessed, albeit only by two young and dedicated British astronomers: Jeremiah Horrocks and William Crabtree.

As from the next pair after 1639, a real transit craze began to shake the scientific community worldwide. As early as 1761, a transit was observed in Rodrigues by astronomer Alexandre-Gui Pingré ? a plaque was unveiled in 1991 at Pointe Vénus to commemorate the event. Pingré?s observations, however, were marred by poor weather. The rich Lord Lindsay also made transit observations from mainland Mauritius, at Belmont near Goodlands in 1874, where the remains of his observatory are still to be seen today.

Excellent visibility, weather permitting

The reason for journeying to the remote parts of the world to observe the transit was that the event gave the only method at the time of accurately determining the distance of the earth to the sun, commonly referred to as the astronomical unit. Knowledge of this distance was then used to determine precisely the absolute scale of other planetary distances within the solar system, which was poorly known before the end of the 19th century. The best determination of the astronomical unit before the invention of modern radar methods was thus obtained by photographic surveys carried out in 1874 by, inter-alia, Lord Lindsay from Mauritius, and also during the 1882 expeditions worldwide.

Prospects, weather permitting, are excellent for Mauritius for the forthcoming 2004 transit, with the entire event being visible locally. The planet is first in contact with the sun at 9.15 hrs, taking almost twenty minutes to cross the solar border. It then begins a leisurely 6 hour long crossing of the sun?s disk, to end completely at 15.26 hours, with maximum transit occurring at 12.21 hrs.

The Mauritius Astronomical Society will display, from 10.00 hrs to 15.00 hours, several motorized and fully filtered telescopes at the Collège du Saint Esprit for public observation of the event on the day. It is needless to say that a sine qua non condition for observation is adequate filtration, whether with the naked eye or with instruments of any kind. Because only a tiny fraction of the dazzlingly bright sun?s disk will be covered by Venus, observing the Sun will be hazardous, and may cause outright blindness, using improper filtration techniques, such as by reflection in water, through welder?s glass, photographic film, sunglasses or smoked glass. Observation is safe through welder?s glass of grade 14 and higher, or through special ?eclipse shades?, but these are not available locally: only grade 11 glass filters are available from local hardware stores.

Our skies at night

The transit of Venus should not make us forget that there are also plenty of features in our evening skies as well during this month of June. The favourable apparition of the planets is nevertheless now coming to an end, but Jupiter is still hanging high in the north-western evening sky, a fine sight with its four Galilean satellites clearly seen in small telescopes up to August, after which it too, like Venus, will be drowned in the sun?s glare but very far away on the other side of the Sun.

Regarding stars and constellations, use of the Star Disk of the Mauritius Astronomical Society (available in all bookstores), will quickly allow an observer to identify the Southern Cross high in the sky soon after sunset. This month also provides a fine opportunity to roam through the Milky Way with the aid of binoculars, particularly into the Scorpius-Sagittarius region practically overhead in the late evening as seen from Mauritius. This region is the centre of our own galaxy, which lies some 30,000 light years away from us, forever hidden from our mortal eyes by dense dust clouds lying directly in our line of sight. In Mauritius, the apparition of the strikingly white star Vega (Alpha Lyrae) in the north east by mid evening certainly announces that chilly winter nights are nigh.

In the movie Contact, an artificial radio signal is received from space that is broadcast from the star, 26 light years away. We also find in that motion picture the terrifying statement that ?if we are alone in space, it would be an awful waste of space?. While it would be too much to ask the radio astronomers at the awe-inspiring Bras d?Eau radio-telescope to confirm this sci-fi radio emission, many arguments have indeed been proposed in reply to the fascinating question: why is there intelligence at all in the universe? Astrophysicist Trinh Xuan Thuan, in his book The Secret Melody, prefers the idea whereby there must necessarily have been a Great Architect, who has engineered the constants of physics to have an unbelievably extreme precision so as to allow the emergence of man (the anthropic principle, which is the idea that we live in a universe fine tuned for life). Father Eamonn Mansfield (1934-1995), founder of the Mauritius Astronomical Society, shared this theological perspective of genesis, highlighting that all sacred texts proclaim that the heavens declare the glory of the almighty, not man. Indeed, if the universe was created only for man?s benefit, then it is a waste of space. Do we deserve it at all? But if the main function of the universe is to glorify a creating entity, it can then be wondered whether it is big enough?