British Astronomical Association
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British Astronomical Association
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Meteor Section |
Autumn is traditionally the busiest time for meteor observers, with several fairly-respectable regular annual showers active, and random background sporadic rates at their highest for the year. Observers frustrated by the moonlight during Perseid maximum can at least use the autumn to keep in practice while obtaining some useful data on less well-covered showers, starting with the Alpha Aurigids as the Moon wanes back to New in late August.
Alpha Aurigids
Active August 25 - September 8
Radiant RA 05h 54m Dec +42o
One of autumn' s more obvious minor showers, the Alpha Aurigids become active as the Perseids die away. In some respects, the shower's very swift
meteors are similar to Perseids, but there is no connection between the two. The Alpha Aurigids produce reasonable numbers of bright, yellowish meteors,
several of which leave behind persistent ionisation trains lingering for a few seconds after the meteor itself has gone. Peak corrected Zenithal Hourly
Rates around September 1-2 are usually of the order of 10, corresponding to observed numbers of 6-7 Alpha
Aurigids per hour. Sometimes, however, the shower may show outbursts of higher activity, as last seen in 1994. The shower is well worth watching in
the late evening and early morning hours, and will be favoured by the absence of moonlight in 2003.
Piscids
Active September to October
Radiant RA 00h 36m Dec +07o (early September)
Throughout most of the year, a steady 'drizzle' of meteor activity comes from near the ecliptic plane. The Piscids are the autumn continuation of
this, producing low rates of slow, moderately bright meteors. At best, perhaps 2-3 Piscids per hour might be seen. Peaks are listed for September 8
and 12, and October 13, but the low rates produced by the shower make these uncertain.
Orionids
Active October 16-30
Radiant RA 06h 24m Dec +15o
Produced by debris from Comet 1P/Halley, the Orionids are autumn's finest regular shower, producing good observed rates (up to 15-20 meteors/hr in
ideal conditions) around their broad peak over October 20-22. The Halley debris stream is made up from interwoven 'filaments' of meteoroids, shed at
separate perihelion returns of the parent comet. This has led to a diffuse (possibly multiple) radiant structure, and the timing of activity peaks
seems to vary from year to year depending on which filaments are encountered by Earth. The radiant area lies between Betelgeuse and Gamma
Geminorum, rising around 22h UT on an October evening. Best rates are found, naturally,
in the early morning hours when the radiant has attained a reasonable altitude above the horizon.
Orionid meteoroids have, like the parent comet, a retrograde orbit around the Sun. Consequently, they impact on the upper atmosphere at very
high velocities, producing extremely swift meteors. A further result of this is that Orionids frequently leave persistent trains. Most
Orionids are in the medium brightness range (magnitude +2 to +4), but there are also a reasonable proportion of bright meteors among the activity.
Moonlight is a major influence on the Orionids in 2003. Last Quarter is on October 18, and the Moon is a bright waning crescent, rising more or
less at the same time as the radiant on Oct 20 and 21. By October 22, the Moon will be retreating further into the morning sky, allowing a slightly
longer 'window' of dark observing conditions. Orionid activity is certainly still worth following late into October's closing week, and observers are
encouraged to make good use of any clear skies in this period.
Taurids
Active October 20 - December 1
Radiants N RA 03h 44m Dec +22o
S RA 03h 44m Dec +14o
Observers covering the Orionids can expect to record occasional slow Taurid meteors during their watches. Produced by debris from Comet 2P/Encke, the
Taurid meteor stream is ancient and has become greatly spread out by planetary perurbations and solar radiation effects, such that its activity
lasts for about 6 weeks. Rates are never particularly high, but a steady 5-6 per hour can be expected during the most active part of the shower in the
early days of November. In common with many other near-ecliptic streams, the Taurids have become split into a couple of branches. The radiant
positions for these at maximum (nominally November 3) are given above; observers should remember that due to Earth's orbital motion, meteor shower
radiants move eastwards by about 1 degree per day, and allowance should be made in back-tracking to determine likely radiant alignment in watches made
at dates substantially removed from peak. At maximum, the northern Taurid radiant lies a little west of the Pleiades, the southern west of the
Hyades.
Taurid meteors are slow, and may occasionally be bright. In some textbooks, they are described as producing frequent fireballs. Analysis of observations in the BAA Meteor Section archives, however, suggests that while reasonable numbers of bright (mag/ 0 to -3, say) Taurids are reported in most years, fireballs (by definition mag. -5 or brighter) as such are no more abundant by proportion than in other showers like the Perseids. It is possible that some years are richer in bright Taurids than others.
Moonlight becomes something of a nuisance in evenings during early November. The Moon reaches First Quarter on November 1, and will be up until after midnight from November 3 onwards. The best time for Taurid observing in 2003 will be in late evening during the closing days of October and the very beginning of November.
Leonids
Active November 15 - 20
Radiant RA 10h 08m Dec +22o
Having commanded - literally! - the lion's share of attention in the past eight years or so, the Leonids should now be declining from the high -
sometimes exceptionally so - activity which followed the parent comet 55P/Tempel-Tuttle's early 1998 perihelion passage. No further
storm activity is anticipated in the current round, and the Leonid 'background' will probably revert to its normal peak ZHR of about 15 in the
next few years. This, it should be stressed, is still a respectable showing by any standards, and serious meteor observers, in for the long haul and
not just the 'glory' nights, will continue to cover the shower in the years ahead.
Unfortunately, circumstances for 2003 are singularly poor, with the Last Quarter Moon close to the shower radiant in Leo's 'Sickle' at peak around Nov 17-18. In the likely absence of elevated activity, there will probably be very little to be seen of the Leonids this year.
Page last updated: 21/11/2003