compiled by Alastair McBeath
based on data in IMO Monograph No.2: Handbook for Visual Meteor Observers,
edited by Jürgen Rendtel, Rainer Arlt and Alastair McBeath, IMO, 1995,
with additional contributions from Rainer Arlt, Marc de Lignie,
Jürgen Rendtel and Paul Roggemans.
Layout by André Knöfel.
Prepared for WWW by Sirko Molau
IMO’s Meteor Shower Calendar for 1998 contains the following items:
- Introduction
- Highlights January to March
- Highlights April to June
- Highlights July to September
- Highlights October to December
- Abbreviations
- Tables
- Lunar phases for 1998
- Working list of visual meteor showers
- Radiant positions during the year in alpha and delta
- Working list of daytime radio meteor streams
- Useful addresses
Introduction
Welcome to the 1998 International Meteor Organization (IMO) Meteor Shower Calendar. This year promises to be an extremely interesting one, with most major showers free from moonlight interference (except the eta-Aquarids and Perseids), the prospect of a Draconid return in October, and a possible meteor storm from the Leonids in November. Do not forget that monitoring of meteor activity should ideally be carried on throughout the rest of the year too, however! We appreciate that this is not practical for many observers, and this Calendar was devised as a means of helping observers deal with reality by highlighting times when a particular effort may most usefully be employed. Although we include to-the-hour predictions for all the more active night-time and daytime shower maxima, based on the best available data, please note that in many cases, such maxima are not known more precisely than to the nearest 1° of solar longitude (even less accurately for the daytime radio showers, which have received little attention in recent years). In addition, variations in individual showers from year to year mean past returns are at best only a guide as to when even major shower peaks can be expected, plus as some showers are known to show particle mass-sorting within their meteoroid streams, the radio, telescopic, visual and photographic meteor maxima may occur at different times from one another, and not necessarily just in these showers. The majority of data available are for visual shower maxima, so this must be borne in mind when employing other observing techniques. The heart of the Calendar is the Working List of Visual Meteor Showers, thanks to regular analyses using the IMO's Visual Meteor Database, the single most accurate listing available anywhere today for naked-eye meteor observing. Even this can never be a complete list of all meteor showers, since there are many showers which cannot be properly detected visually, and some which only photographic, radar, telescopic, or video observations can separate from the background sporadic meteors, present throughout the year. The IMO's aims are to encourage, collect, analyze, and publish combined meteor data obtained from sites all over the globe in order to further our understanding of the meteor activity detectable from the Earth's surface. Results from only a few localized places can never provide such total comprehension, and it is thanks to the efforts of the many IMO observers worldwide since 1988 that we have been able to achieve as much as we have to date. This is not a matter for complacency, however, since it is solely by the continued support of many people across the whole world that our steps towards constructing a better and more complete picture of the near- Earth meteoroid flux can proceed. This means that all meteor workers, wherever they are and whatever methods they use to record meteors, should follow the standard IMO observing guidelines when compiling their information, and submit their data promptly to the appropriate Commission for analysis. Visual and photographic techniques remain popular for nightly meteor coverage (weather permitting), although both suffer considerably from the presence of moonlight. Telescopic observations are less popular, although they allow the fine detail of shower radiant structures to be derived, and they permit very low activity showers to be accurately detected. Video methods have been dynamically applied in the last few years, and are starting to bear considerable fruit. These have the advantages, and disadvantages, of both photographic and telescopic observing, but are already increasing in importance. Radio receivers can be utilized at all times, regardless of clouds, moonlight, or daylight, and provide the only way in which 24-hour meteor observing can be accomplished for most latitudes. Together, these methods cover virtually the entire range of meteoroid sizes, from the very largest fireball-producing events (using all-sky photographic patrols or visual observations) through to tiny dust grains producing extremely faint telescopic or radio meteors. However and whenever you are able to observe, we wish you all a most successful year's work and very much look forward to receiving your data. Clear skies!
The opening quarter of the year brings several low activity showers, including the first of the year's main diffuse ecliptical stream complexes, the Virginids, active from late January to mid-April. Of the two better showers, only the northern-hemisphere Quadrantids in early January are free from moonlight. The other, the alpha-Centaurids, a sometimes good southern hemisphere shower (maximum around February 7, 16h UT) is too close to full Moon for non-radio observations. The minor delta-Cancrids in mid-January lose out too to a bright Moon, along with the gamma-Normids in mid-March. Daylight radio peaks are due from the Capricornids/Sagittarids around 13h UT on February 1, and the chi-Capricornids on February 13, probably around 14h UT. Neither radio shower has been well-observed in recent times, and as both have radiants under 10°-15° west of the Sun at maximum, they cannot be regarded as visual targets even from the southern hemisphere.
Active : January 1-5; Maximum : January 3, 17h UT (lambda = 283.16°); ZHR = 120 (can vary around 60-200); Radiant : alpha = 230°, delta = +49°; Radiant drift: see Table 3; Radius : 5° at maximum; V = 41 km/s; r = 2.1 at maximum, but variable; TFC : alpha = 242°, delta = +75° and alpha = 198°, delta = +40° (beta>40° N); PFC : before 00h local time alpha = 150°, delta = +70°; after 00h local time alpha = 180°, delta = +40° and alpha = 240°, delta = +70° (beta>40° N). Figure 1: Radiant position of the Quadrantids [image:843] The year commences with a good return of the Quadrantids for northern hemisphere observers, as the Moon will be a waxing crescent setting by the local late evening hours of January 3. Since the shower's radiant is in northern Bootes, it is circumpolar for many northern locations, but it attains a useful elevation only after local midnight or so, and gets higher towards morning twilight. The Moon will thus present no problems in 1998. An interesting challenge is to try spotting the occasional long-pathed shower member from the southern hemisphere around dawn, but sensible Quadrantid watching cannot be carried out from such locations. The maximum time given above is based on the best-observed return of the shower ever analysed, from IMO 1992 data, confirmed by radio results in 1996 and 1997, and a repeat of which time in 1998 would favour sites from Alaska and the Northern Pacific islands to Far Eastern Siberia, China and Japan. The peak itself is short-lived, and can be easily missed in just a few hours of poor winter weather in the north, which may be why the ZHR level apparently fluctuates from year to year, but some genuine variability is probably present too. An added level of complexity comes from the fact that mass-sorting of particles across the meteoroid stream may make fainter objects (radio and telescopic meteors) reach maximum up to 14 hours before the brighter (visual and photographic) ones, so observers should be alert throughout the shower! Past observations have suggested the radiant is very diffuse away from the maximum, contracting notably during the peak itself, although this may be a result of the very low activity normally seen away from the hours near maximum. Photographic and video observations from January 1-5 would be particularly welcomed by those investigating this topic, using the PFCs and TFCs given above, along with telescopic and visual plotting results.
Active : February 15 - March 10; Maximum : February 24 (lambda = 336°); ZHR = 2; Radiant : alpha = 168°, delta = +16°; Radiant drift: see Table 3; Radius : 5°; V = 23 km/s; r = 3.0; TFC : alpha = 140°, delta = +37° and alpha = 151°, delta = +22° (beta>10° N); alpha = 140°, delta = -10° and alpha = 160°, delta = 0° (beta<10° N). Figure 2: Radiant position of the delta-Leonids [image:53] This minor shower is probably part of the early Virginid activity. Rates are normally low, and its meteors are predominantly faint, so it is a prime candidate for telescopic investigation. Visual observers must make very accurate plots of the meteors to distinguish them from the nearby Virginids and the sporadics. Northern hemisphere sites have a distinct advantage for covering this stream, whose radiant is well on view for most of the night near the peak, close to the "Sickle" or "Head" of Leo, but southern hemisphere watchers should not ignore it, as they are better-placed to note many of the other Virginid radiants. With the Moon just two days before new at the shower's maximum, conditions could scarcely be better for observing it.
April to June
Meteor activity picks up towards the April-May boundary, with showers like the Lyrids, p-Puppids and h-Aquarids, and only this latter source suffers from moonlight this year. During May and June, most of the activity is in the daytime sky, with six shower peaks expected during this time. Although a few shower members from the o-Cetids and Arietids have been reported from tropical and southern hemisphere sites visually in previous years, sensible activity calculations cannot be carried out from such observations. For radio observers, the expected UT maxima for these showers and the Moon- affected h- Aquarids are as follows: April Piscids -- April 20, 13h UT; delta-Piscids -- April 24, 13h UT; eta-Aquarids -- May 6, 04h UT; epsilon-Arietids -- May 9, 12h UT; May Arietids -- May 16, 13h UT; o-Cetids -- May 20, 11h UT; Arietids -- June 7, 15h UT; zeta-Perseids -- June 9, 14h UT; beta-Taurids -- June 28, 14h UT. The ecliptical complexes continue with some late Virginids and the best from the minor Sagittarids in May-June.
Active : April 16-25; Maximum : April 22, 10h UT (lambda = 32.1°); ZHR = 15 (can be variable, up to 90); Radiant : alpha = 271°, delta = +34°; Radiant drift: see Table 3; Radius : 5°; V = 49 km/s; r = 2.9; TFC : alpha = 262°, delta = +16° and alpha = 282°, delta = +19° (beta>10° S). Figure 3: Radiant position of the Lyrids [image:54] The Lyrids are best viewed from the northern hemisphere, but they are observable from many sites either north or south of the equator, and are suitable for all forms of observation. Maximum rates are usually attained for only an hour or two at best, although in 1996, mean peak ZHRs of 15-20 persisted for around 8-12 hours. The ZHR can be rather erratic at times, a variability also seen in 1996, when rates ranged between 10-30 from hour to hour during the peak. The last high maximum occurred in 1982 over the USA, when a very short-lived peak ZHR of 90 was recorded. This unpredictability always makes the Lyrids a shower to watch, since we cannot say when the next unusual return may occur. As the shower's radiant rises during the night, watches can be usefully carried out from about 22:30 local time onwards. This year, the Moon will be a waning crescent in Capricornus/Aquarius for the peak, and will rise not long before dawn, so skies should remain dark for much of the night. The predicted maximum should favour sites across North America if correct, but variations in the stream could mean this is not the case in actuality.
Active : April 15-28; Maximum : April 23, 20h UT (lambda = 33.5°); ZHR : periodic, up to around 40; Radiant : alpha = 110°, delta = -45°; Radiant drift: see Table 3; radius : 5°; V = 18 km/s; r = 2.0; TFC : alpha = 135°, delta = -55° and alpha = 105°, delta = -25° (beta<20° N). Figure 4: Radiant position of the pi-Puppids [image:55] This is a young stream produced by Comet 26P/Grigg-Skjellerup, and shower activity has only been detected from it since 1972. Notable short-lived shower maxima of around 40 meteors per hour took place in 1977 and 1982, both years when the parent comet was at perihelion, but before 1982, little activity had been seen at other times. In 1983, a ZHR of about 13 was reported, perhaps suggesting that material has begun to spread further along the comet's orbit, as theory predicts. Comet Grigg-Skjellerup was due at perihelion on 1997 August 30, but in 1997 an almost full Moon coincided with the shower's peak. At the 1998 return, we reach the closest-approach point to the orbit almost eight months after the comet, so this will be a useful year to check for pi-Puppid activity further from the comet, especially as the Moon is just three days from new for the maximum. The shower is best-seen from the southern hemisphere, with useful observations mainly possible before local midnight, as the radiant is very low or setting after 1h local time. So far, visual and radio data have been collected on the shower, but the slow, bright nature of the meteors makes them ideal photographic subjects too. No telescopic or video data have been reported in any detail as yet either.
Minor shower activity continues apace from near-ecliptic sources throughout this quarter, first from the Sagittarids, then the Aquarid and Capricornid showers (discussed below with the Piscis Austrinids; the Southern iota- Aquarid and Northern delta-Aquarid maxima lose out to August's full Moon), and finally the Piscids into September. Other showers that vanish into bright moonlight this quarter include the Pegasids and Phoenicids in July; the Perseids in August (coverage is still important, but will be exceptionally difficult with a waning gibbous Moon; the maxima are predicted for August 12, 14h UT and August 12, 22h UT); and the alpha- and delta-Aurigids in September (alpha-Aurigid peak due around September 1, 05h UT). At least the minor kappa-Cygnids still survive this moonlight onslaught! For daylight radio observations, the interest of May-June has waned, but there remain the visually-inaccessible gamma-Leonids (peak due August 25d 14h UT), and a tricky visual shower, the Sextantids (maximum expected September 27d 14h UT). The latter has no problems from the waxing crescent Moon, but its radiant will rise less than an hour before dawn ineither hemisphere.
Piscis Austrinids and Aquarid/Capricornid Complex
Active : July 15-August 10; Maximum : July 28 (lambda = 125°); ZHR = 5; Radiant : alpha = 341°, delta = -30°; Radiant drift: see Table 3; Radius : 5°; V = 35 km/s; r = 3.2; TFC : alpha = 255° to 0°, delta = 0° to +15°, choose pairs separated by about 30° in alpha (beta<30° N). Figure 5: Radiant position of the Piscis Austrinids [image:669]
Active : July 12-August 19; Maximum: July 28, 06h UT (lambda = 125°); ZHR = 20; Radiant : alpha = 339°, delta = -16°; Radiant drift: see Table 3; Radius : 5°; V : 41 km/s; r = 3.2; TFC : alpha = 255° to 0°, delta = 0° to +15°, choose pairs separated by about 30° in alpha (beta<40° N). Figure 6: Radiant position of the Southern and Northern delta-Aquarids [image:668]
Active : July 3-August 15; Maximum : July 30 (lambda = 127°); ZHR = 4; Radiant : alpha = 307°, delta = -10°; Radiant drift: see Table 3; Radius : 8°; V = 23 km/s; r = 2.5; TFC : alpha = 255° to 0°, delta = 0° to +15°, choose pairs separated by about 30° in alpha (beta<40° N). PFC : alpha = 300°, delta = +10° (beta>45° N), alpha = 320°, delta = -05° (beta = 0° to 45° N), alpha = 300°, delta = -25° (beta<0° S.) Figure 7: Radiant position of the Alpha Capricornids [image:668]
Active : August 11-31; Maximum : August 20 (lambda = 147°); ZHR = 3; Radiant : alpha = 327°, delta = -6°; Radiant drift: see Table 3; Radius : 5°; V = 31 km/s; r = 3.2; TFC : alpha = 255° to 0°, delta = 0° to +15°, choose pairs separated by about 30° in alpha (beta<40° N). Figure 8: Radiant position of the Southern and Northern iota-Aquarids [image:669] The Aquarids and Piscis Austrinids are all rich in faint meteors, making them well-suited to telescopic work, although enough brighter members exist to make visual and photographic observations worth the effort too, primarily from more southerly sites. Radio work can be used to pick up the Southern delta-Aquarids especially, as the most active of these showers. The alpha-Capricornids are noted for their bright - sometimes fireball- class - events, which, combined with their low apparent velocity, can make some of these objects among the most impressive and attractive an observer could wish for. A minor enhancement of alpha-Capricornid ZHRs to around 10 was noted in 1995 by European IMO observers, although the Southern delta- Aquarids were the only one of these streams previously suspected of occasional variability. Such a concentration of radiants in a small area of sky means that familiarity with where all the radiants are is essential for accurate shower association for all observing nights. Visual watchers in particular should plot all potential stream members seen in this region of sky rather than trying to make shower associations in the field. The only exception is when the Southern delta-Aquarids are near their peak, as from southern hemisphere sites in particular, rates may become too high for accurate plotting. All the above listed shower maxima are almost free from lunar interference in 1998. The Piscis Austrinid, Southern delta-Aquarid and alpha-Capricornid maxima have only a waxing crescent Moon to contend with, while August's new Moon falls favourably for the Northern iota-Aquarid peak. All these radiants are above the horizon for much of the night.
Active : August 3-25; Maximum : August 18, (lambda = 145°); ZHR = 3; Radiant : alpha = 286°, delta= +59°; Radiant drift: see Table 3; Radius : 5°; V = 25 km/s; r = 3.0; TFC : alpha = 330°, delta = +60° and alpha = 300°, delta = +30° (beta> 20° N). The waning crescent Moon will rise during the local early morning hours at the kappa-Cygnid peak this year, a very minor nuisance only for watchers north of the equator, where the shower is chiefly accessible from. Its r- value suggests telescopic and video observers may benefit from its presence, but visual and photographic workers should note that occasional slow fireballs from this source have been reported too. Its almost stationary radiant results from its close proximity to the ecliptic north pole in Draco. There has been some suggestion of a variation in its activity at times, perhaps coupled with a periodicity in fireball sightings, but more data are urgently needed on a shower that often is ignored in favour of the Perseids during August.
Active : September 1-30; Maximum : September 20, (lambda = 177°); ZHR = 3; Radiant : alpha = 5°, delta= -1°; Radiant drift: see Table 3; Radius : 5°; V = 26 km/s; r = 3.0; TFC : alpha = 340° to 20°, delta = -15° to +15°, choose pairs separated by about 30° in alpha (beta any). Figure 9: Radiant position of the Piscids [image:64] The Piscids are a poorly-studied minor shower, with a radiant very close to the March equinox point in the sky. Consequently, they can be studied equally well from either hemisphere throughout the night near the September equinox, close to their probable maximum time. This year, new Moon falls exactly on September 20, but there is some doubt as to exactly when the Piscid peak may occur - or indeed, if there is only the one. Telescopic and video methods can be usefully employed to study it, along with careful visual plotting.
October to December
Ecliptical minor shower activity reaches what might be regarded as a peak in early to mid November, with the Taurid streams in action (the Southern Taurid maximum will be lost to bright moonlight this year, but something of the Northern peak should still be seen). Before then come an important return of the Draconids, the Orionid and the minor epsilon-Geminid maxima. This is also a key year for the Leonids in November, and a good one to check for a repeat of 1995's outburst for the alpha-Monocerotids. December's full Moon claims the maxima of the chi-Orionids, Phoenicids (December 6, 13h UT) and the early, better, part of the weak Puppid-Velid complex, as well as much of the Monocerotids and sigma-Hydrids. This does mean the Geminids, Coma Berenicids and Ursids are all much better-placed with regard to the Moon.
Active : October 6-10; Maximum : October 8, 17-23h, (lambda = 159.40°), ZHR = periodic, up to storm levels; Radiant : alpha = 262°, delta = +54°; Radiant drift: negligible; Radius : 5°; V = 20 km/s; r = 2.6; TFC : alpha = 290°, delta = +65° and alpha = 288°, delta = +39° (beta>30° N). Despite the presence of a waning gibbous Moon, which will rise within 2-3 hours of nightfall for the northern hemisphere sites this shower is visible from, 1998 is a very important year for observing the Draconids. This periodic shower has produced spectacular, brief, meteor storms twice already this century, in 1933 and 1946, and lower rates in several other years (ZHRs around 20-200+), most recently in 1985. So far, detectable activity has only been seen in years when the stream's parent comet, 21P/Giacobini-Zinner, has returned to perihelion, which it is expected to do again in 1998 November. Perturbations of the stream, coupled with the fact that the 1946 event remains the best-observed return, mean predicting when activity might occur is very difficult. The spread in solar longitudes at which notable past activity has been detected is from lambda = 195.26° (1985) to lambda = 197.0° (1933), which equates to times between October 8, 17h UT and October 10, 12h UT in 1998. This is certainly a period that all observers should be alert to, using a full range of techniques, but with the Earth expected to pass the comet's node at lambda = 195.398° (October 8, 21 h UT), times earlier in this period may be more likely. The peak time given in the box above is a mean value of the previous returns, and should be viewed more as a general guide than an absolute value. The radiant, near Draco's "Head", is circumpolar from many locations, but is higher in the pre-midnight and near-dawn hours on October 8-10. Photographic and video data would be especially valuable in case high rates do take place.
Active : October 14-27; Maximum : October 18, (lambda = 205°), ZHR = 2; Radiant : alpha = 102°, delta = +27°; Radiant drift: see Table 3; Radius : 5°; V = 70 km/s; r = 3.0; TFC : alpha = 90°, delta = +20° and alpha = 125°, delta = +20° (beta>20° S). A weak minor shower, whose meteors are very like the Orionids, active, and at maximum, around the same time, so great care must be taken to separate the two sources by instrumental techniques - especially video or telescopic work - or visual plotting. New Moon on October 20 presents an excellent opportunity to obtain more data on them from either hemisphere, although northern observers have an advantage. The radiant is higher only after midnight.
Active : October 2 - November 7; Maximum : October 21, (lambda = 208°), ZHR = 20; Radiant : alpha = 95°, delta = +16°; Radiant drift: see Table 3; Radius : 10°; V = 66 km/s; r = 2.9; TFC : alpha = 100°, delta = +39° and alpha = 75°, delta = +24° (beta>40° N); or alpha = 80°, delta = +1° and alpha = 117°, delta = +1° (beta<40° N). Figure 10: Radiant position of the Orionids and epsilon-Geminids [image:66] October's new Moon enhances the Orionids this year too. They are noted for having several maxima other than the main one detailed above, with activity sometimes remaining almost constant for several consecutive nights centred on this peak. In 1993, a submaximum as strong as the normal peak was detected on October 17-18 from Europe, for instance. All observers should be aware of these possibilities. Several subradiants have been reported in the past, but recent video work suggests the radiant is far less complex; photographic, telescopic and video work to confirm this would be useful, as visual observers have clearly had problems with this shower's radiant determination before. With a radiant almost on the celestial equator, the shower can be seen from most of the globe, and observations are possible from midnight onwards in both hemispheres, perhaps a little before in the north.
Active : November 14-21; Maximum : November 17, 19h UT (lambda = 235.25°), ZHR = 40+ (45 in 1996), but may reach storm levels in 1998-99; Radiant : alpha = 153°, delta = +22°; Radiant drift: see Table 3; Radius : 5°; V = 71 km/s; r = 2.9; TFC : alpha = 140°, delta = +35° and alpha = 129°, delta = +6° (beta>35° N); or alpha = 156°, delta = -3° and alpha = 129°, delta = +6° (beta<35° N); PFC : before 00h local time alpha = 120°, delta = +40° (beta>40° N); before 04h local time alpha = 120°, delta = +20° (beta>40° N); and after 04h local time alpha = 160°, delta = 0° (beta>40° N); before 00h local time alpha = 120°, delta = +10° (beta>0° N) and alpha = 160°, delta = -10° (beta<0° N). Figure 11: Radiant position of the Leonids [image:68] The recovery of the Leonids' parent comet, 55P/Tempel-Tuttle, on 1997 March 4 has raised hopes further that a storm of Leonids might occur in 1998 or 1999. There are, of course, no guarantees that this will happen, but all observers must realise that even discovering the absence of any unusual Leonid activity would still be very valuable information - albeit not all that interesting to witness! Visual IMO International Leonid Watch and radio observations in 1996 indicated quite a broad Leonid maximum between lambda = around 235.1°-235.4° (equivalent to 1998 November 17, 14h-22h UT), with one minor peak at lambda = 235.17° (1998 November 17, 17h UT). As the Earth should pass the node of the comet's orbit around 1998 November 17, 19h UT (lambda = around 235.3°), this may well be the most likely time for the very highest activity to occur. As the radiant, in Leo's "Head" or "Sickle" asterism, rises only around local midnight (or indeed afterwards south of the equator), places in the Far East, including China, Eastern Siberia and Japan, south through the Western Pacific islands to Australia, should be the favoured spots, if the maximum keeps to this time. Even a minor variation could mean places east or west of this zone may see something of the shower's best too, however. Look out for further updates in the IMO's journal WGN after the 1997 return. The Moon is just two days from new on November 17, so it will cause no problems this year, and all observing methods should be utilised to the full, especially photography and video if a storm manifests.
Active : November 15-25; Maximum : November 21, 20h UT (lambda = 239.32°), ZHR = variable, usually around 5 but may produce outbursts to around 400+; Radiant : alpha = 117°, delta = +1°; Radiant drift: see Table 3; Radius : 5°; V = 65 km/s; r = 2.4; TFC : alpha = 115°, delta = +23° and alpha = 129°, delta = +20° (beta>20° N); or alpha = 110°, delta = -27° and alpha = 98°, delta = +6° (beta<20° N); Another late-year shower capable of producing surprises, the alpha- Monocerotids gave their most recent brief outburst in 1995 (the top EZHR, around 420, lasted just five minutes; the entire outburst 30 minutes). Many observers across Europe witnessed it, and we have been able to completely update the known shower parameters as a result. Whether this indicates the propsed ten-year periodicity in such returns is real or not, only the future will tell, however, so all observers should continue to monitor this source closely. New Moon on November 19 makes this an excellent year for such scrutiny, with the radiant well on view in both hemispheres after about 23h local time or so.
Active : December 7-17; Maximum : December 14, 05h UT (lambda = 262.0°), ZHR = 120; Radiant : alpha = 112°, delta = +33°; Radiant drift: see Table 3; Radius : 5°; V = 35 km/s; r = 2.6; TFC : before 23h local time alpha = 87°, delta = +20° and alpha = 135°, delta = +49°; after 23h local time alpha = 87°, delta = +20° and alpha = 129°, delta = +20° (beta>40° N); alpha = 120°, delta = -3° and alpha = 84°, delta = +10° (beta<20° N); PFC : alpha = 150°, delta = +20° and alpha = 60°, delta = +40° (beta>20° N); and alpha = 135°, delta = -5° and alpha = 80°, delta = 0° (beta<20° N) Figure 12: Radiant position of the Geminids [image:72] One of the finest annual showers presently observable, their early stages will be lost to moonlight this year, but their peak occurs with a waning crescent Moon which should present few problems, and then only late in the night. Well north of the equator, the radiant rises around sunset, and can be usefully observed from the local evening hours onwards, but in the southern hemisphere, the radiant appears only around local midnight or so. Even here, this is a splendid stream of often bright, medium-speed meteors, a rewarding sight for all watchers. The peak has shown slight signs of variability in its maximum rates and the actual peak timing (ZHRs were around 110 around lambda 262.2°-262.4° in 1996, for instance), so the best activity may occur a little before or after the suggested time above. Even so, European, African, Near Eastern and American sites are the most likely beneficiaries of the very best Geminid rates in 1998. Some mass- sorting within the stream means the fainter telescopic meteors should be most abundant almost 1° of solar longitude ahead of the visual maximum, with telescopic results indicating these meteors radiate from an elongated region, perhaps with three sub-centers. Further results on this topic would be useful, but all observing methods can be employed to observe the shower.
Active : December 12 - January 23; Maximum : December 20, (lambda = 268°), ZHR = 5; Radiant : alpha = 175°, delta = +25°; Radiant drift: see Table 3; Radius : 5°; V = 65 km/s; r = 3.0; TFC : alpha = 180°, delta = +50° and alpha = 165°, delta = +20° before 03h local time; or alpha = 195°, delta = +10° and alpha = 200°, delta = +45° after 03h local time (beta>20° N). Figure 13: Radiant position of the Coma Berenicids [image:73] A weak minor shower that is usually observed only during the Geminid and Quadrantid epochs, but which needs more coverage at other times too, especially to better-define its maximum. The shower is almost unobservable from the southern hemisphere, so northern watchers must brave the winter cold to improve our knowledge of it, especially this year as its expected peak is just two days after new Moon. The radiant is at a useful elevation from local midnight onwards.
Active : December 17-26; Maximum : December 22, 18h UT (lambda = 270.7°); ZHR = 10 (occasionally variable up to 50); Radiant : alpha = 217°, delta = +76°; Radiant drift: see Table 3; radius : 5°; V = 33 km/s; r = 3.0; TFC : alpha = 348°, delta = +75° and alpha = 131°, delta = +66° (beta>40° N); alpha = 63°, delta = +84° and alpha = 156°, delta = +64° (beta 30° to 40° N); Figure 14: Radiant position of the Ursids [image:672] A very poorly-observed northern hemisphere shower, but one which has produced at least two major outbursts in the past half-century or so, in 1945 and 1986. Several other rate enhancements, recently in 1988 and 1994, have been reported too. Other similar events could easily have been missed due to poor weather or too few observers active. All forms of observation can be used for the shower, since many of its meteors are faint, but with so little work carried out on the stream, it is impossible to be precise in making statements about it. The radio maximum in 1996 occurred around lambda 270.8°, for instance, which might suggest a slightly later maximum time in 1998 of December 22, 20h UT. The Ursid radiant is circumpolar from most northern sites (thus fails to rise for most southern ones), though it culminates after daybreak, and is highest in the sky later in the night. The waxing crescent Moon will give dark skies for observations almost all night on December 22.
alpha, delta: Coordinates for a shower's radiant position, usually at maximum; is right ascension, is declination. Radiants drift across the sky each day due to the Earth's own orbital motion around the Sun, and this must be allowed for using the details in Table 3 for nights away from the listed shower maxima. r: Population index, a term computed from each shower's meteor magnitude distribution. r = 2.0-2.5 is brighter than average, while r above 3.0 is fainter than average. lambda: Solar longitude, a precise measure of the Earth's position on its orbit which is not dependent on the vagaries of the calendar. All lambda are given for the equinox J2000.0. v: Atmospheric or apparent meteoric velocity given in km/s. Velocities range from about 11 km/s (very slow) to 72 km/s (very fast). 40 km/s is roughly medium speed. ZHR: Zenithal Hourly Rate, a calculated maximum number of meteors an ideal observer would see in a perfectly clear skies with the shower radiant overhead. This figure is given in terms of meteors per hour. Where meteor activity persisted at a high level for less than an hour, or where observing circumstances were very poor, an estimated ZHR (EZHR) is used, which is less accurate than the normal ZHR. TFC and PFC: suggested telescopic and photographic field centers respectively. beta is the observer's latitude ("<" means "south of" and ">" means "north of"). Pairs of telescopic fields must be observed, alternating about every half hour, so that the positions of radiants can be defined. The exact choice of TFC or PFC depends on the observer's location and the elevation of the radiant. Note that the TFCs are also useful centres to use for video camera fields as well.
Table 1: Lunar phases for 1998. New First Full Last Moon Quarter Moon Quarter January 5 January 12 January 20 January 28 February 3 February 11 February 19 February 26 March 5 March 13 March 21 March 28 April 3 April 11 April 19 April 26 May 3 May 11 May 19 May 25 June 2 June 10 June 17 June 24 July 1 July 9 July 16 July 23 July 31 August 8 August 14 August 22 August 30 September 6 September 13 September 20 September 28 October 5 October 12 October 20 October 28 November 4 November 11 November 19 November 27 December 3 December 10 December 18 December 26
Table 2: Working list of visual meteor showers. Details in this Table correct according to the best information available in June 1997. Contact the IMO's Visual Commission for more information. Maximum dates in parentheses indicate reference dates for the radiant, not true maxima. Some showers have ZHRs that vary from year to year. The most recent reliable figure is given here, except for possibly periodic showers that are noted as "var." = variable. Shower Activity Maximum Radiant Period Date lambda alpha delta ° ° ° Quadrantids Jan 01-Jan 05 Jan 03 283.16 230 +49 delta-Cancrids Jan 01-Jan 24 Jan 17 297 130 +20 alpha-Centaurids Jan 28-Feb 21 Feb 07 318.7 210 -59 delta-Leonids Feb 15-Mar 10 Feb 24 336 168 +16 gamma-Normids Feb 25-Mar 22 Mar 13 353 249 -51 Virginids Jan 25-Apr 15 (Mar 24)(004) 195 -04 Lyrids Apr 16-Apr 25 Apr 22 032.1 271 +34 pi-Puppids Apr 15-Apr 28 Apr 23 033.5 110 -45 eta-Aquarids Apr 19-May 28 May 05 045.5 338 -01 Sagittarids Apr 15-Jul 15 (May 20)(059) 247 -22 Pegasids Jul 07-Jul 13 Jul 10 108 340 +15 July Phoenicids Jul 10-Jul 16 Jul 13 111 032 -48 Pisces Austrinids Jul 15-Aug 10 Jul 28 125 341 -30 Southern delta-Aquarids Jul 12-Aug 19 Jul 28 125 339 -16 alpha-Capricornids Jul 03-Aug 15 Jul 30 127 307 -10 Southern iota-Aquarids Jul 25-Aug 15 Aug 04 132 334 -15 Northern delta-Aquarids Jul 15-Aug 25 Aug 08 136 335 -05 Perseids Jul 17-Aug 24 Aug 12 140.0 046 +58 kappa-Cygnids Aug 03-Aug 25 Aug 18 145 286 +59 Northern iota-Aquarids Aug 11-Aug 31 Aug 20 147 327 -06 alpha-Aurigids Aug 25-Sep 05 Sep 01 158.6 084 +42 delta-Aurigids Sep 05-Oct 10 Sep 08 166 060 +47 Piscids Sep 01-Sep 30 Sep 20 177 005 -01 Draconids Oct 06-Oct 10 Oct 08 195.4 262 +54 epsilon-Geminids Oct 14-Oct 27 Oct 18 205 102 +27 Orionids Oct 02-Nov 07 Oct 21 208 095 +16 Southern Taurids Oct 01-Nov 25 Nov 05 223 052 +13 Northern Taurids Oct 01-Nov 25 Nov 12 230 058 +22 Leonids Nov 14-Nov 21 Nov 17 235.25 153 +22 alpha-Monocerotids Nov 15-Nov 25 Nov 21 239.32 117 +01 chi-Orionids Nov 26-Dec 15 Dec 02 250 082 +23 Phoenicids Nov 28-Dec 09 Dec 06 254.25 018 -53 Puppid-Velids Dec 01-Dec 15 (Dec 07)(255) 123 -45 Monocerotids (Dec) Nov 27-Dec 17 Dec 09 257 100 +08 sigma-Hydrids Dec 03-Dec 15 Dec 12 260 127 +02 Geminids Dec 07-Dec 17 Dec 14 262.0 112 +33 Coma Berenicids Dec 12-Jan 23 Dec 20 268 175 +25 Ursids Dec 17-Dec 26 Dec 22 270.7 217 +76
Shower v r ZHR IMO km/s Code Quadrantids 41 2.1 120 QUA delta-Cancrids 28 3.0 4 DCA alpha-Centaurids 56 2.0 6 ACE delta-Leonids 23 3.0 2 DLE gamma-Normids 56 2.4 8 GNO Virginids 30 3.0 5 VIR Lyrids 49 2.9 15 LYR pi-Puppids 18 2.0 var. PPU eta-Aquarids 66 2.7 60 ETA Sagittarids 30 2.5 5 SAG Pegasids 70 3.0 3 JPE July Phoenicids 47 3.0 var. PHE Pisces Austrinids 35 3.2 5 PAU Southern delta-Aquarids 41 3.2 20 SDA alpha-Capricornids 23 2.5 4 CAP Southern iota-Aquarids 34 2.9 2 SIA Northern delta-Aquarids 42 3.4 4 NDA Perseids 59 2.6 90 PER kappa-Cygnids 25 3.0 3 KCG Northern iota-Aquarids 31 3.2 3 NIA alpha-Aurigids 66 2.5 10 AUR delta-Aurigids 64 3.0 6 DAU Piscids 26 3.0 3 SPI Draconids 20 2.6 var. GIA epsilon-Geminids 70 3.0 2 EGE Orionids 66 2.9 20 ORI Southern Taurids 27 2.3 5 STA Northern Taurids 29 2.3 5 NTA Leonids 71 2.5 40+ LEO alpha-Monocerotids 65 2.4 var. AMO chi-Orionids 28 3.0 3 XOR Phoenicids 18 2.8 var. PHO Puppid-Velids 40 2.9 10 PUP Monocerotids (Dec) 42 3.0 3 MON sigma-Hydrids 58 3.0 2 HYD Geminids 35 2.6 120 GEM Coma Berenicids 65 3.0 5 COM Ursids 33 3.0 10 URS
Table 3: Radiant positions during the year in alpha and delta. COM DCA Jan 0 186 +20 112 +22 QUA Jan 5 190 +18 116 +22 231 +49 Jan 10 194 +17 121 +21 Jan 20 202 +13 130 +19 ACE VIR Jan 30 200 -57 157 +16 DLE Feb 10 214 -60 165 +10 155 +20 GNO Feb 20 225 -63 172 +6 164 +18 225 -53 Feb 28 178 +3 171 +15 234 -52 Mar 10 186 0 180 +12 245 -51 Mar 20 192 -3 256 -50 Mar 30 198 -5 Apr 10 SAG LYR PPU 203 -7 Apr 15 224 -17 263 +34 106 -44 ETA 205 -8 Apr 20 227 -18 269 +34 109 -45 323 -7 Apr 25 230 -19 274 +34 111 -45 328 -5 Apr 30 233 -19 332 -4 May 5 236 -20 337 -2 May 10 240 -21 341 0 May 20 247 -22 350 +5 May 30 256 -23 Jun 10 265 -23 Jun 15 270 -23 Jun 20 275 -23 Jun 25 280 -23 Jun 30 284 -23 CAP JPE Jul 5 289 -22 285 -16 SDA 338 +14 Jul 10 293 -22 PHE 289 -15 325 -19 NDA 341 +15 PER PAU Jul 15 298 -21 032 -48 294 -14 329 -19 316 -10 012 +51 330 -34 Jul 20 299 -12 333 -18 319 -9 SIA 018 +52 334 -33 Jul 25 303 -11 337 -17 323 -9 322 -17 023 +54 338 -31 Jul 30 KCG 308 -10 340 -16 327 -8 328 -16 029 +55 343 -29 Aug 5 283 +58 NIA 313 -8 345 -14 332 -6 334 -15 037 +57 348 -27 Aug 10 284 +58 317 -7 318 -6 349 -13 335 -5 339 -14 043 +58 352 -26 Aug 15 285 +59 322 -7 352 -12 339 -4 345 -13 050 +59 Aug 20 286 +59 327 -6 AUR 356 -11 343 -3 057 +59 Aug 25 288 +60 332 -5 076 +42 347 -2 065 +60 Aug 30 289 +60 337 -5 082 +42 DAU Sep 5 088 +42 055 +46 SPI Sep 10 060 +47 357 -5 Sep 15 066 +48 001 -3 Sep 20 071 +48 005 -1 Sep 25 NTA STA 077 +49 009 0 Sep 30 021 +11 023 +5 ORI 083 +49 013 +2 Oct 5 025 +12 027 +7 085 +14 089 +49 GIA Oct 10 029 +14 031 +8 088 +15 095 +49 262 +54 Oct 15 034 +16 035 +9 091 +15 EGE Oct 20 038 +17 039 +11 094 +16 099 +27 Oct 25 043 +18 043 +12 098 +16 104 +27 Oct 30 047 +20 047 +13 101 +16 109 +27 Nov 5 053 +21 052 +14 105 +17 Nov 10 058 +22 056 +15 LEO AMO Nov 15 062 +23 060 +16 150 +23 112 +2 Nov 20 067 +24 064 +16 XOR 153 +21 116 +1 Nov 25 072 +24 069 +17 075 +23 120 0 MON PUP PHO Nov 30 080 +23 HYD 091 +8 120 -45 014 -52 Dec 5 COM GEM 085 +23 122 +3 096 +8 122 -45 018 -53 Dec 10 169 +27 108 +33 090 +23 126 +2 100 +8 125 -45 022 -53 Dec 15 173 +26 113 +33 094 +23 130 +1 URS 104 +8 128 -45 Dec 20 177 +24 118 +32 217 +75
Table 4: Working list of daytime radio meteor streams. The "Best Observed" columns give the approximate local mean times between which a four-element antenna at an elevation of 45° receiving a signal from a 30-kW transmitter 1000 km away should record at least 85% of any suitably positioned radio- reflecting meteor trails for the appropriate latitudes. Note that this is often heavily dependent on the compass direction in which the antenna is pointing, however, and applies only to dates near the shower's maximum. Shower Activity Max lambda Radiant Best Observed Rate Date 2000.0 al. de. 50°N 35°S ° ° ° Cap/Sagittarids Jan 13-Feb 04 Feb 02 312.5 299 -15 11h-14h 09h-14h medium chi-Capricornids Jan 29-Feb 28 Feb 14 324.7 315 -24 10h-13h 08h-15h low Piscids (Apr.) Apr 08-Apr 29 Apr 20 030.3 007 +7 07h-14h 08h-13h low delta-Piscids Apr 24-Apr 24 Apr 24 034.2 011 +12 07h-14h 08h-13h low epsilon-Arietids Apr 24-May 27 May 08 048.7 044 +21 08h-15h 10h-14h low Arietids (May) May 04-Jun 06 May 16 055.5 037 +18 08h-15h 09h-13h low o-Cetids May 05-Jun 02 May 19 059.3 028 -4 07h-13h 07h-13h medium Arietids May 22-Jul 02 Jun 07 076.7 044 +24 06h-14h 08h-12h high zeta-Perseids May 20-Jul 05 Jun 09 078.6 062 +23 07h-15h 09h-13h high beta-Taurids Jun 05-Jul 17 Jun 28 096.7 086 +19 08h-15h 09h-13h medium gamma-Leonids Aug 14-Sep 12 Aug 25 152.2 155 +20 08h-16h 10h-14h low Sextantids Sep 09-Oct 09 Sep 27 184.3 152 0 06h-12h 06h-13h medium
For more information on observing techniques, and when submitting results, please contact the appropriate IMO Commission Director: Fireball Data Center : André Knöfel, Saarbrückerstraße 8, (FIDAC) D-40476 Düsseldorf, Germany. (e-mail: fidac@imo.net) Photographic Commission: Marc de Lignie, Prins Hendrikplein 42, NL-2264 SN Leidschendam, the Netherlands. (e-mail: photo@imo.net) Radio Commission: Temporarily vacant (e-mail: radio@imo.net) Telescopic Commission: Malcolm Currie, 25 Collett Way, Grove, Wantage, Oxon. OX12 0NT, UK. (e-mail: tele@imo.net) Visual Commission: Rainer Arlt, Berliner Straße 41, D - 14467 Potsdam, Germany (e-mail: visual@imo.net) or contact IMO's Homepage in the World-Wide-Web: http://www.imo.net/ For further details on IMO membership, please write to: Ina Rendtel, IMO Treasurer, Gontardstraße 11 D-14471 Potsdam, Germany. (e-mail: treasurer@imo.net) Please try to enclose return postage when writing to any IMO officials, either in the form of stamps (same country only) or as an International Reply Coupon (I.R.C.--available from main postal outlets). Thank you!