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Following several years in which enhanced activity has been clearly apparent, the Leonids were expected to show rather more ‘normal’ rates in 2004, with their parent, Comet 55P/Tempel-Tuttle, now more than six years past perihelion. By this time, encounters between Earth and the denser ‘ortho Leonid’ material relatively close to the parent comet’s nucleus can be considered less likely, and we should see a return to the lower (though still respectable) ‘clino Leonid’ activity seen in, say, the 1980s. In recent years a revised model of the ortho Leonids has emerged, based on distinct ‘filaments’ of debris shed from the comet at separate perihelion returns. This model has been used successfully by David Asher and Robert McNaught, Esko Lyytinen and others to predict the timing (though not necessarily the intensity) of strong, even storm, peaks in the Leonids between 1999 and 2002.
An interesting prediction for 2004 suggested a possible distant encounter between Earth and a Leonid filament from the 1001 perihelion (30 revolutions ago!) late on 8 November - almost a week before the nominal start of the shower’s usual activity. No confirmatory observations have been reported in the literature.
Extending the series of possible filament encounters of recent years were predictions for the 1333 (20 revolution) trail early on Nov 19d, and the 1733 (8 revolution) trail late on Nov 19d. Closest passage to the mean stream/comet orbit occurred around Nov 17d 09h UT; this is normally the clino Leonid maximum, as quoted in the BAA Handbook. With the passage of time since Comet Tempel-Tuttle’s perihelion, the possible major filament encounters have come progressively later, those on Nov 19d being only a day or so from the normal end of the shower’s annual activity.
Unlike the strongly-moonlit 2003 return, the Leonids of 2004 were favoured by dark skies, with the Moon a waxing crescent setting before midnight local time around Nov 17d. Once again, however, poor weather held sway for observers in the UK. A total of only 12H 59m formal watch time, amounting to a 131 meteors (35 sporadics, 77 Leonids, 19 Taurids) has been reported by:
J Abbott, N Bone, A Ibrahim, T Lloyd Evans, G Spalding, M Stephens.
Observing between 0155-0305 UT on November 17-18, Ayman Ibrahim at Hirghada, Egypt reported 3 sporadics and 10 Leonids - certainly not exceptional activity - a few hours ahead of the annual maximum.
The one well-covered night from the UK was November 18-19, with good skies and modest Leonid rates between 02h UT and dawn about four hours later. Corrected ZHRs of the order of 15-25 are found from the available data. There is nothing to suggest unusually strong Leonid activity at this time - nor was any great enhancement forecast for the ca. 06h 42m UT encounter with the 1333/20-rev trail. Formal analysis figures are given below, but it should be borne in mind that these are based on relatively small samples:
| 2004 Nov |
Sol. long. |
Teff |
Av. LM |
F |
NSp |
CHR |
NLeo |
Alt. Rad. (o) |
ZHR |
| 19d02h46m |
237.06 |
1.00 |
6.30 |
- |
7 |
9.0±3.4 |
8 |
39.0 |
15.3±5.4 |
| 03 46 |
237.10 |
1.00 |
6.30 |
- |
4 |
5.1±2.6 |
4 |
46.5 |
6.6±3.3 |
| 04 15 |
237.12 |
1.00 |
6.00 |
1.06 |
3 |
5.9±3.4 |
11 |
52.9 |
23.1±7.0 |
| 04 50 |
237.15 |
2.00 |
5.90 |
- |
7 |
7.3±2.8 |
13 |
54.3 |
13.9±3.9 |
| 05 15 |
237.16 |
1.00 |
5.41 |
- |
3 |
11.5±4.6 |
5 |
58.8 |
15.9±7.1 |
From his favourable clear-sky location in southern France, Michael Stephens recorded 10 Leonids in LM 5.0 conditions from 0408-0508 UT on Nov 19-20, suggesting ZHR around 45 (with the caveat that the dataset is still on the small side!). James Abbott in Witham, Essex, noted 4 Leonids in a casual 15-minute inspection of the sky up to 01h UT on the same night. No reports suggesting particularly high activity at these times have appeared elsewhere. As in past years, a reasonable number of bright Leonids were in evidence, though no fireballs have been reported. Best was a mag. -4 Leonid with a 7-second persistent train seen from Sussex and Oxfordshire at Nov 19d 05h 18m UT. Trains were left by 50% of Leonids, compared with 11.5% of sporadics. |
