IF you read these words midmorning Saturday, the writer, all going well, will be in an aeroplane somewhere over eastern Europe, speeding homewards after a meeting about weather satellites in Turkey,
The text has been written nearly seven days before, but an astronomical prediction, unlike a long range weather forecast, is so uncannily dependable that one can be absolutely sure that the prescribed event will indeed take place on schedule.
Thus, a week in advance, I can confidently forecast that there will be a partial eclipse of the sun about 2 p.m. until 4.30 p.m. this afternoon.
A solar eclipse occurs when the moon in its circumambulation around the Earth passes directly between our planet and the sun. It obscures our view of the solar disc or, viewed from space, the moon casts a shadow on the surface of the Earth. Since the moon is tiny compared to Earth, it casts only a small shadow, a circle about 150 miles in diameter that skims rapidly from west to east across the surface.
Today this shadow will move from north east Canada across Greenland and Iceland, and then over Europe before disappearing over western Asia. This eclipse is a partial one which means that at most, some 60 per cent of the solar disc will be obscured.
The impact of a solar eclipse is largely due to a curious coincidence. It so happens that viewed from Earth, the apparent size of the lunar disc exactly matches that of the face of the sun.
In round figures, the sun is 400 times as big as the moon, but it is 400 times further away from us, so the two bodies appear from our vantage point to be very similar in size - a fact which can be verified by the even most casual observer of the skies.
Throughout the ages, eclipses have often been regarded at best as a bad omen and at worst as the malign influence of an evil spirit.
They signalled the death of the sun or moon, a threat to the established order and more or less the end of civilisation at that time. A popular concept in many cultures saw the event as an attack by a fierce monster - a dragon, a lion or an evil serpent - which proceeded to devour the body in the heavens.
It was generally accepted that the only way of warding off this great catastrophe was to create a noise, known variously as "hullabaloo" or "pandemonium", by banging drums and pots and pans. The noise never failed after a time to frighten the devouring monster and forced it to release the sun or moon.
Indeed, this remedy still works, as you may verify yourself if you put it to the test this afternoon.