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Meteor Shower Could Spur Bright Fireballs

November 1, 2008
Space.com

The Taurid meteors, sometimes called the "Halloween fireballs," show up between mid-October and mid-November, but November 5 to 12 will likely be the best time to look for them this year, taking into account both their peak of activity and the effect of increasingly bright moonlight on viewing conditions.

After the Moon sets - around 11 p.m. local time on Nov. 5, later on subsequent nights - some 10 to 15 meteors may appear per hour. They are often yellowish-orange and, as meteors go, appear to move rather slowly. Their name comes from the way they seem to radiate from the constellation Taurus, the Bull, which sits low in the east a couple of hours after sundown and is almost directly overhead by around 1:30 a.m.

Meteors - popularly referred to as "shooting stars" - are generated when debris enters and burns up in Earth's atmosphere. In the case of the Taurids, they are attributed to debris left behind by Encke's Comet, or perhaps by a much larger comet that upon disintegrating, left Encke and a lot of other rubble in its wake.

Indeed, the Taurid debris stream contains noticeably larger fragments than those shed by other comets, which is why in certain years - and 2008 is predicted to be one - this rather elderly meteor stream occasionally delivers a few unusually bright meteors known as "fireballs."

Two streams

The Taurids are actually divided into the Northern Taurids and the Southern Taurids. This is an example of what happens to a meteor stream when it grows old.

Even at the beginning, the particles could not have been moving in exactly the same orbit as their parent comet; their slight divergence accumulates with time. Meantime the Sun is not the only body gravitationally controlling the particles' orbits; the planets are having subtle effects on the stream. As the positions of the planets are constantly changing, the particles pass nearer to them on some revolutions than others - diverting parts of the stream, fanning it out and splitting it.

So what was originally one stream diffuses into a cloud of minor streams and isolated particles in individual orbits, crossing Earth's orbit at yet more widely scattered times of the year and coming from more scattered directions until they are entirely stirred into the general haze of dust in the solar system.

Another fireball year?

Dr. Victor Clube, an English astrophysicist and is an expert on comets and cosmology, indicated back in 1992 that the Taurid meteor stream contains perhaps a half a dozen full-size asteroids whose orbits place them squarely in the stream. Clube and his colleagues argue that the Taurids' range of orbits indicates they were all shed by a huge comet, originally 100 miles across or more, that entered the inner solar system some 20,000 years ago.

By 10,000 years ago it was desiccated and brittle; Encke's Comet might actually be the biggest leftover chunk.

Encke's has the shortest known orbital period for a comet, taking only 3.3 years to make one complete trip around the sun. Meteor expert David Asher has also discovered that the Earth can periodically encounter swarms of larger particles in certain years and 2008 is predicted to be one of those years.

In the September 2008 issue of "Meteor Trails" (the journal of the American Meteor Society), Robert Lunsford writes: "Maximum rates for the southern branch occur near November 5th and the northern branch peaks near November 12th. This year the Moon is favorable during the first week of November but the northern Taurids peak only a day before full Moon."

The two radiants lie just south of the Pleiades. So during the next couple of weeks, if you see a bright, slightly tinted orange meteor sliding rather lazily away from that famous little smudge of stars, you can feel sure it is a Taurid.

Adds Lunsford: "2005 was the last swarm year . . . many exceptional fireballs were seen especially along the U.S. East Coast on Halloween evening when fireballs as bright as the full Moon were witnessed.

Will 2008 offer a repeat performance? Only by going out and viewing this display will we know for sure!"

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