Science: Stars And Planets: December
Friday 27 November 1998
Meanwhile, friends and colleagues who'd been up the previous night had been phoning in with descriptions of some brilliant fireworks early on the 17th. Meteors as bright as Venus; shooting stars that cast shadows; the odd fireball that rivalled the full Moon. One colleague was even woken by the brilliance of a fireball exploding outside his curtains.
Astronomers across Europe and beyond filed reports of brilliant Leonids that morning, falling at a rate of ten every minute. British astronomers in the Canary Islands saw even more, a meteor every few seconds, as dawn rose over the Atlantic. By the time Leo rose in the US, rates were down to one or two per minute. This was also the rate seen by disappointed astronomers in Japan and China, and the overflying Nasa scientists.
There was no great meteor storm to rival years such as 1966, when the US was treated to a sky filled with meteors falling like snow - up to 20 meteors every second. In these terms, the display seen from Europe this year was just a heavy shower.
What went wrong? Iwan Williams, of Queen Mary and Westfield College in London, whose cautious prediction for 1998 of four meteors per minute, was one of the most accurate, points out that the interplanetary debris causing the Leonid display does not come in a single stream. Most astronomers had focused on a dense bunch of debris, shed from comet Tempel-Tuttle, which intersects the Earth once in 33 years, and creates a true storm. Williams says that the Earth missed this dense patch, or maybe clipped its fringes. That's why there was no storm over east Asia.
But there is also a thin sprinkling of particles scattered around the comet's orbit, which gives us a meagre shower every year, about one meteor every five to ten minutes. In the excitement over a possible storm, many astronomers had neglected this "normal annual peak". But this year the tenuous stream was much denser than expected - and that's what hit us in the early morning of 17 November, exactly on time.
What does this mean for next year? Professor Williams is pessimistic. "The whole stream is drifting away from the Earth, so the normal peak may be enhanced but not as much as this year."
On the other hand, if we happen to hit the dense bunch of debris in 1999, there will be a storm visible over Europe that will dwarf this year's show. So we'll be taking no chances next year, even if it means losing two or three nights' sleep!
WHAT'S UP: Jupiter is still brilliant all evening, shining brighter than any of the stars. With good binoculars look for its four biggest moons. A small telescope will reveal some of the bands of cloud that stretch around the giant planet.
Turn your telescope to another bright "star" to the left of Jupiter, and you'll see the spectacular sight of Saturn and its famous rings, now tilted towards the Earth and visible in all their splendour. And a small telescope will show Saturn's largest moon, Titan, when it is furthest from the planet's glare, around 5, 13, 21 and 29 December.
Early on 14 December, look out for a shower of shooting stars from the northeast. You may catch one or two of these Geminid meteors each minute, streaming out from the Gemini constellation, the twins. Unlike most meteors, shed by comets, the Geminids are debris from an asteroid, called Phaethon.
NIGEL HENBEST AND
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