British Astronomical Association
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British Astronomical Association
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Meteor Section |
Following the relatively low January to March activity, with minimal background sporadic rates and only minor showers present, April brings a welcome upturn. A favourable return of the Lyrids kicks off the more productive parts of what should be a very good year for meteor observing, with the majority of the most prolific showers well-placed with respect to moonlight.
Lyrids
Active April 19-25
Radiant RA 18h 08m Dec +32o
With New Moon falling on April 19 the Lyrids are, in 2004, blessed by dark sky conditions. On maximum night - Wednesday-Thursday 21-22 April - the Moon will be a 3-day waxing crescent, setting around midnight and not therefore interfering with observations during the early morning hours when the shower radiant is best placed. Lyrids emanate from a radiant some 10 degrees southwest (to the lower right in the UK) of Vega, near the Lyra/Hercules border. The radiant is low in the northeast at nightfall, but climbs rapidly and is well up in the east by the end of the night (all else being equal, most meteors will be seen from a shower when its radiant is higher in the sky).
Lyrid meteors are produced by debris from Comet C/1861 G1 Thatcher, ad are swift (geocentric velocity 49 km/sec). Bright Lyrids are reasonably abundant, and the brightest meteors often leave behind short-duration persistent trains.
Activity shows a reasonably sharp peak, expected around 2004 Apr 22d 02h UT - early in the morning for UK observers, and at a time when the radiant is high. In most years, peak corrected Zenithal Hourly Rate (ZHR; allowing for sky transparency and the elevation of the radiant above the horizon) is of the order of 10-15, corresponding to typical observed rates of 8-10 meteors/hr in reasonable conditions. The Lyrids have, however, produced outbursts of higher activity in past years: most recently, ZHR ca 100-200 was found for a brief spell in 1982.
Some reasonable observations were obtained by BAAMS members in 2003, indicating another 'normal' return with a reasonable crop of bright Lyrids, though observed rates were pegged back somewhat by haze conditions over much of the UK. Hopefully, we will have more transparent conditions for the well-timed, Moon-free 2004 return! Observers are, naturally, encouraged to make use of clear sky opportunities on all nights possible during the whole span of the Lyrids' activity period.
Pons-Winneckids
Active June 26-July 2
Radiant RA 14h 56m Dec +47o
Produced by debris from the short-period comet 7P/Pons-Winnecke, this shower has an interesting observational history. Substantial displays were seen in 1916, 1921 and 1927 associated with then-recent perihelion returns of the parent comet. Subsequent gravitational perturbations by Jupiter pulled the comet orbit outwards from that of the Earth by a large and, from the point of view of producing meteor activity, unfavourable 0.24 astronomical units. It therefore came as something of a surprise when a significant display of Pons-Winneckid meteors occurred on 1998 June 27-28, with observed rates up to 60 meteors/h over a roughly 12-hour period extending to about June 28d 03h UT. Later calculations by Asher and Emil'yanenko suggested that the outburst was produced by debris released from the parent comet at its 1825 perihelion, remaining in a 2:1 orbital/gravitational resonance with Jupiter. It is considered likely that we shall again encounter this material in 2004, bringing the possibility of a significant display peaking around 01h UT on the Saturday night to Sunday morning of June 26-27.
Pons-Winneckid meteors emanate from a radiant in northern Bootes (some European observers refer to the shower as the 'June Bootids'). The meteors are very slow, with geocentric velocity 14 km/sec. A characteristic of showers with such slow meteors - October's periodic Giacobinids are another example - is that the radiant is rather diffuse and poorly defined. Observations in 1998 showed most Pons-Winneckid meteors to be in the medium-to-faint magnitude rage; bright events were comparatively scarce.
Little if any Pons-Winneckid activity has been reported in the years since 1998: alerted by that year's unexpected return, observers have been on careful lookout! Certainly, nothing out of the ordinary happened in 2003: (The parent comet was back at perihelion in May 2002, but the material responsible for the outbursts is long-separated from it, and there is no reason to correlate high meteor activity with the comet's current movements).
The possible 2004 return will be accompanied by a waxing gibbous Moon (9 days old), low to the southwest around midnight UT. This shouldn't interfere too badly with observations, given that for UK observers the night sky at this time of year is essentially twilit in any case. Watches should be made by standard methods (outlined below); in the unlikely event of rates becoming higher than 5 meteors/minute, observers should concentrate on making counts, rather than recording magnitude, time and train data for individual meteors. The short summer night will restrict watches to only a couple of hours' duration, but it is still important that observers at least try to follow what activity, if any, is produced by the Pons-Winneckids this year - remember that negative reports are also of value, and should be submitted to the Meteor Section!
Despite the success of new models in forecasting the occurrence and timing of recent Leonid storms, there is no absolute guarantee that the forecast Pons-Winneckid activity will manifest in 2004 - actual naked eye, visual observations are essential to find out what's really going on.
Observations of the Lyrids and Pons-Winneckids will, as always, be welcomed by the Meteor Section Director at the address given in the Journal of the BAA.
August brings a very favourable return of the Perseids, peaking on Aug 12-13, for which observing notes will appear on these pages closer to the event.
Page last updated: 30/08/2004