Astronomers Predict Spectacular
The Leonid meteor shower is expected to produce a particularly spectacular display in November 1998 according to Professor Iwan Williams of Queen Mary and Westfield College, University of London, who has been studying what is known about the stream of meteoroids in space which is responsible for the shower. Professor Williams presents his findings at the UK's National Astronomy Meeting at Southampton University on Friday 11th April 1997. The Leonids produce grand displays about every 33 years. The last time was in 1966, but 1998 could be better than 1999, Professor Williams says.
Meteor streams are formed from the dust grains released by the nucleus of a comet when it gets near to the Sun and becomes active. If the Earth's orbit crosses through the meteor stream, we experience a meteor shower. Over time, the dust grains spread slowly round the comet's orbit. When they are distributed around the whole of the orbit, the same number of meteors are seen at about the same time each year. However, this is not the case with the Leonids.
The Leonids are dust from comet Temple-Tuttle, discovered in 1865, but that dust is still in a large clump close to the comet. It has not had enough time to spread all round the orbit. That means that the Leonids produce large numbers of meteors when Earth is near the comet - about every 33 years - and are rather sparse or non-existent at other times.
Professor Williams says that his calculations suggest 'the display will be spectacular but not awesome, - that is several thousand meteors per hour rather than tens or even hundreds of thousand as has been the case on some occasions in the past.' He also thinks 1998 will possibly be the best year rather than 1999 since the comet's closest approach to Earth is between the two dates but closer to November 1998.
The start of the serious scientific study of meteors is generally attributed to the spectacular display produced by the Leonids in November 1833. It was studies of this shower that led to the observation that the meteors appeared to originate from a single point, or radiant, in the sky. This was correctly interpreted as signifying that the meteoroids move on essentially parallel tracks in the solar system, as a stream. In the case of the Leonids, the radiant is in the constellation Leo - hence the name of the shower.
The mathematician John Couch Adams (1819-1892) (who also predicted the existence of the planet Neptune) studied changes in the Leonid stream and concluded that the orbital period of the Leonid meteors was about 33.25 years. This was remarkably similar to that of the newly discovered Comet Temple-Tuttle. It was also soon realized that spectacular displays of the Leonid stream had occurred at the same interval. Good displays were seen in 1799, 1833 and 1866. Since then, spectacular displays occurred around 1900 and in 1966.