International Meteor Organization
IMO Meteor Shower Calendar 1997
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, and
contributions from Paul Roggemans. Layout by André Knöfel.
Prepared for UseNet, CompuServe and AstroNet by André Knöfel
prepared for WWW by Sirko Molau
IMOs Meteor Shower Calendar for 1997 contains the following items:
- Introduction
- Highlights January to March
- Highlights April to June
- Highlights July to September
- Pegasids
- July Phoenicids
- Piscis Austrinids and Aquarid/Capricornid Complex
- Piscis Austrinids
- Southern delta-Aquarids
- alpha-Capricornids
- Southern iota-Aquarids
- Northern delta-Aquarids
- Perseids
- alpha- and delta-Aurigids
- Highlights October to December
- Abbreviations
- Tables
- Lunar phases for 1997
- 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 1997 International Meteor Organization (IMO) Meteor Shower Calendar. In response to suggestions from radio workers, we have included information on the predicted timing of the more active night-time and daytime shower maxima this year, based on the best available data. It should be noted, however, that in many cases, such maxima are not known more precisely than to the nearest 1deg of solar longitude (even less accurately for the daytime radio showers, which have received little attention in recent years), and 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. In addition, several showers are known to show particle mass-sorting within their meteoroid streams, which means that 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. In an ideal world, of course, we would like to see global monitoring of the meteor activity the Earth encounters throughout the year whenever conditions permit, to enable us to better understand the meteoroid flux in the near-Earth vicinity. This Calendar was devised as a means of helping observers to deal with reality, where such protracted observing is often not possible, in highlighting times when a particular effort may most usefully be employed. 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 meteor activity near the Earth 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 still 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 alreadyincreasing 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!
January to March
The first quarter of the year brings primarily low activity showers, including the first of the year's main diffuse ecliptical stream complexes, the Virginids, active from late January to mid-April. The two better showers, the Quadrantids, visible from the northern hemisphere in early January, and the alpha-Centaurids, a sometimes good southern hemisphere shower in early February, are both free from moonlight in 1997, along with the minor delta-Cancrids in mid-January and the gamma-Normids in mid-March. Two daylight radio peaks are due from the Capricornids/Sagittarids around 07h UT on February 1, and the -Capricornids on February 13, probably around 08h 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.
Quadrantids
Active : January 1-5; Maximum : January 3, 11h UT (lambda = 283.16°); ZHR = 120 (can vary around 60-200); Radiant : alpha = 230°, delta = +49°; Radiant drift: see Table 3; diameter : 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 QuadrantidsThe year starts well for northern hemisphere watchers, with a reasonably good return of the Quadrantids, since the Moon will be a waning crescent in eastern Virgo and western Libra on January 3-4, and will give its worst problems only late in the night. The shower's radiant lies in northern Bootes, which makes it circumpolar for many northern locations, but it attains a useful elevation for observations only after local midnight or so, and is at its highest towards morning twilight. It is an interesting challenge to try spotting the occasional long-pathed shower member from the southern hemisphere around dawn, but sensible 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, a repeat of which time in 1997 would be excellent news for North American watchers. 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 makes 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 observations from January 1-6 would be particularly welcomed by those investigating this topic, using the PFCs given above, along with telescopic, video and visual plotting results.
delta-Cancrids
Active : January 1-24; Maximum : January 17 (lambda = 297°); ZHR = 4; Radiant : alpha = 130°, delta = +20°; Radiant drift: see Table 3; size : alpha = 20° x delta = 10°; V = 28 km/s; r = 3.0; TFC : alpha = 115°, delta = +24° and alpha = 140°, delta = +35° (beta>40° N); alpha = 120°, delta = -03° and alpha = 140°, delta = -03° (beta<40° N). Figure 2: Radiant position of the delta-CancdridsThis minor stream is especially suited to telescopic observations, with its large, complex radiant area that may consist of several sub-centers, and many of its meteors are faint. It is likely that this shower is an early part of the Virginid activity, which generally becomes more obvious in March and April. The delta-Cancrid ZHR is unlikely to rise much above 3-4, but the long winter nights in the northern hemisphere provide a good opportunity to see what occurs, particularly this year, with the Moon at first quarter for the shower's peak. The radiant is above the horizon for almost the entire night, whether your site is north or south of the equator, with moonset around local midnight.
alpha-Centaurids
Active : January 28-February 21; Maximum : February 7, 10h UT (lambda = 318.7°); ZHR = variable, usually around 6, but may reach 25+; Radiant : alpha = 210°, delta = 59°; Radiant drift: see Table 3; radius : 4°; V = 56 km/s; r = 2.0. Figure 3: Radiant position of the alpha-CentauridsThe alpha-Centaurids are one of the main southern hemisphere high points in the opening months of the year, producing many very bright, even fireball- class objects (meteors of at least magnitude -3). Their peak ZHR is normally around 5-10, but in 1974 and again in 1980, bursts of only a few hours duration that yielded activity closer to 20-30 were detected. As we have no means of telling when another such event might happen, photographic,video and visual observers are urged to be alert, especially this year, since the new Moon on February 7 perfectly favours the maximum. Thanks to their brilliance, even a normal alpha-Centaurid return is worth looking out for, and almost one-third routinely leave fine persistent trains after them. The radiant is nearly circumpolar for much of the sub-equatorial Earth, and is at a useful elevation from late evening onwards.
gamma-Normids
Active : February 25-March 22; Maximum : March 13, (lambda = 353°); ZHR = 8; Radiant : alpha = 249°, delta= -51°; Radiant drift: see Table 3; radius : 5°; V = 56 km/s; r = 2.4; TFC : alpha = 225°, delta = -26° and alpha = 215°, delta = -45° (beta< 15° S). Figure 4: Radiant position of the gamma-Normidsgamma-Normid meteors are very similar to the sporadics in appearance, and for most of their activity period, their ZHR is virtually undetectable above this background rate. The peak itself is normally quite sharp, with ZHRs of 3+ noted for only a day or two to either side of the maximum. There are suggestions that the activity may vary somewhat at times, with occasional broader, or less obvious, maxima having been reported in the past. Post-midnight watching yields best results, when the radiant is rising to a reasonable elevation from southern hemisphere sites, which is good news in 1997, as the Moon is a waxing crescent that will have set long before this time on March 13. All forms of observation can be carried out for them, although most northern observers will see nothing from the shower.
April to June
Meteor activity picks up around the April-May boundary, with showers like the Lyrids, pi-Puppids and eta-Aquarids, albeit only this latter source is free from moonlight this year. For radio observers, the expected UT maxima for the April showers are as follows: April Piscids (possibly periodic daylight shower) -- April 20d 07h; Lyrids -- April 22d 03h; pi-Puppids -- April 23d 14h; delta-Piscids (very short daylight shower) -- April 24d 07h. During May and June, most of the activity is in the daytime sky, with six shower peaks due in 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. These daylight showers have the following predicted UT maximum times in 1997: epsilon-Arietids -- May 9d 05h; May Arietids -- May 16d 06h; o-Cetids -- May 20d 05h; Arietids -- June 7d 09h; zeta-Perseids -- June 9d 08h; beta-Taurids -- June 28d 08h. The ecliptical complexes continue with some late Virginids and the best from the minor Sagittarids in May-June.
eta-Aquarids
Active : April 19-May 28; Maximum : May 5, 22h UT (lambda = 45.5°); ZHR = 60 (occasionally variable); Radiant : alpha = 338°, delta = -01°; Radiant drift: see Table 3; radius : 4°; V = 66 km/s; r = 2.7; TFC : alpha = 319°, delta = +10° and alpha = 321°, delta = -23° (beta<20° S). Figure 5: Radiant position of the eta-AquaridsThis is a fine, rich stream associated with Comet 1P/Halley, like the Orionids of October, but it is visible for only a few hours before dawn essentially from tropical and southern hemisphere sites. Occasional meteors have been reported from further north, and the shower would benefit from increased observer activity generally. The fast and often bright meteors make the wait for radiant-rise worthwhile, and many events leave glowing persistent trains after them. A relatively broad maximum -- sometimes with a variable number of submaxima -- usually occurs in early May, and ZHRs are generally above 30 for almost a week centred on the main maximum, based on IMO observations between 1988-1995. With new Moon on May 6, the shower is ideally-placed for watchers in 1997. All forms of observing can be used to study it, with radio work allowing activity to be followed even from northern sites throughout the daylight morning hours. The radiant culminates at about 08h local time.
July to September
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; only the Northern iota-Aquarid maximum loses out particularly to moonlight this year), and finally the Piscids into September. Other low activity showers are apparent too, such as the Pegasids and July Phoenicids, but the kappa-Cygnids lose out to the near-full Moon on August 17. Then there are the Aurigid showers from late August through to October. The major northern hemisphere event is always the Perseids in August, of course. For daylight radio observations, the interest of May-June has waned, but there remains the visually- inaccessible gamma-Leonids (peak due August 25d 08h UT), and a tricky visual shower, the Sextantids (maximum expected September 27d 08h UT). The latter has the waning crescent Moon near its radiant at maximum in 1997, and will rise less than an hour before dawn in either hemisphere.
Pegasids
Active : July 7-13; Maximum : July 10 (lambda = 108°); ZHR = 3; Radiant : alpha = 340°, delta = +15°; Radiant drift: see Table 3; radius : 5°; V = 70 km/s; r = 3.0; TFC : alpha = 320°, delta = +10° and alpha = 332°, delta = +33° (beta>40° N); alpha = 357°, delta = +02° (beta<40° N). Figure 6: Radiant position of the PegasidsWatching this very short-lived minor shower is not easy, as a few cloudy nights mean its loss for visual observers, but with the Moon a waxing crescent for its peak this year, everyone -- particularly those in the northern hemisphere -- should attempt to cover it. The shower is best-seen in the second half of the night, by when the Moon will have set, though the maximum ZHR is generally low. With its swift, faint meteors, telescopic observers should be in action too.
July Phoenicids
Active : July 10-16; Maximum : July 14 (lambda = 111°); ZHR = variable 3-10, usually around 2; Radiant : alpha = 032° , delta = -48°; Radiant drift: see Table 3; radius : 7°; V = 47 km/s; r = 3.0; TFC : alpha = 041°, delta = -39° and alpha = 066°, delta = -62° (beta<10° N). Figure 7: Radiant position of the July PhoenicidsThis minor shower can be seen from the southern hemisphere, from where it only attains a reasonable elevation above the horizon after midnight. This means 1997 is a good year to watch it, with the waxing gibbous Moon at maximum setting as the radiant becomes more suitably--placed. Activity can be quite variable visually, and indeed observations show it is a richer radio meteor source (possibly also telescopically too, but more results are needed). Recent years have brought ZHRs of around 2, when the winter weather has allowed any coverage at all. Perhaps 1997 will be a good year for them?
Piscis Austrinids and Aquarid/Capricornid Complex
Piscis Austrinids
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).
Southern delta-Aquarids
Active : July 12-August 19; Maximum: July 28, 00h 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<30° N). Figure 9,11: Radiant position of the Alpha Capricornids and the Southern and Northern delta-Aquarids
alpha-Capricornids
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<30° 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 8,10: Radiant position of the Piscis Austrinids and the Southern and Northern iota-Aquarids
Southern iota-Aquarids
Active : July 25-August 15; Maximum : August 4 (lambda = 132°); ZHR = 2; Radiant : alpha = 333°, delta = -15°; Radiant drift: see Table 3; radius : 5°; V = 34 km/s; r = 2.9; TFC : alpha = 255° to 0°, delta = 0° to +15°, choose pairs separated by about 30° in alpha (beta<30° N).
Northern delta-Aquarids
Active : July 15-August 25; Maximum : August 8 (lambda = 136°); ZHR = 4; Radiant : alpha = 335° , delta = -05°; Radiant drift: see Table 3; radius : 5°; V = 42 km/s; r = 3.4; TFC : alpha = 255° to 0°, alpha = 0° to +15°, choose pairs separated by about 30° in alpha (beta<30° N). 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 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 possible 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 nights being observed on. 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, when from southern hemisphere sites in particular, rates may become too high for accurate plotting. All the above listed shower maxima are reasonably free from lunar-light interference in 1997, since all five fall between last quarter Moon in late July and first quarter Moon in mid August. As the radiants are above the horizon for much of the night, there is ample scope for extended observing sessions.
Perseids
Active : July 17-August 24;
Maxima : August 12, 06h UT (lambda = 139.6°) and
August 12, 18h UT (lambda = 140.1°);
ZHR : primary peak = variable 150-400, secondary peak = 100;
Radiant : alpha = 046°, delta = +57°;
Radiant drift: see Table 3;
radius : 5°;
V = 59 km/s;
r = 2.6;
TFC : alpha = 019°, delta = +38° and
alpha = 348°, delta = +74° before 2h local time;
alpha = 043°, delta = +38° and
alpha = 073°, delta = +66° after 2h local time (beta>20° N);
PFC : alpha = 300°, delta = +40°,
alpha = 000°, delta = +20° or
alpha = 240°, delta = +70° (beta>20° N).
Figure 12: Radiant position of the Perseids
The Perseids have become the single most exciting and dynamic meteor shower
in recent times, with outbursts producing EZHRs of 400+ in 1991 and 1992,
around 300 in 1993, 220 in 1994 and around 160 in 1995 at the shower's
primary maximum, which this year is expected to fall around 06h UT on
August 12. The peak may be encountered up to four hours before this time,
however, judging by past variations in the densest stream core. The return
of the Perseids' parent comet 109P/Swift-Tuttle in late 1992 was almost
certainly responsible for producing these recent outbursts, although the
material was probably laid down at the comet's previous perihelion passage,
in 1862. Whether the moon-free 1996 Perseid peak will continue the
decreasing trend in the primary maximum's rates remains to be seen as this
is written, but conditions are reasonable for trying to cover the 1997
event, as the waxing gibbous Moon will set soon after midnight for most
northern hemisphere observers on August 12, by when the shower radiant will
be at a very healthy elevation. Europe or the eastern seaboards of North
America should be the places to be, if the shower's primary peak keeps to
time. The "traditional" maximum is expected around 18h UT on August 12,
well-placed for sites in the Far East and eastern Asia particularly.
Visual and photographic observers should need little encouragement to cover
this stream, but telescopic watching near the main peak would be valuable
in confirming or clarifying the possibly multiple nature of the Perseid
radiant, something not detectable visually. Video observations would be
very helpful in this respect too. Radio data would naturally enable early
confirmation, or detection, of a perhaps otherwise unobserved outburst if
the timing proves unsuitable for land-based sites. The only negative aspect
to the shower is the impossibility of covering it from the bulk of the
southern hemisphere.
alpha- and delta-Aurigids
alpha-Aurigids
Active : August 25-September 5; Maximum : August 31, 23hUT (lambda = 158.6°); ZHR = 10; Radiant : alpha = 084°, delta = +42 ; Radiant drift: see Table 3; radius : 5°; V = 66 km/s; r = 2.5. TFC : alpha = 052°, delta = +60°, alpha = 043°, delta = +39° and alpha = 023°, delta = +41° (beta>10° S).
delta-Aurigids
Active : September 5 - October 10; Maximum : September 8 (lambda = 166°); ZHR = 6; Radiant : alpha = 060° , delta = +47°; Radiant drift: see Table 3; radius : 5°; V = 64 km/s; r = 3.0. TFC : alpha = 052°, delta = +60°, alpha = 043°, delta = +39° and alpha = 023°, delta = +41° (beta>10° S). Figure 13: Radiant position of the alpha- and delta-AurigidsThese are both essentially northern hemisphere showers, and are in need of more observations. Despite occurring close to one another in time, and radiating from the same constellation, they are separate streams. The alpha-Aurigids are the more active, with short, unusual bursts giving EZHRs of about 30-40 in 1935, 1986 and 1994, although they have not been regularly observed until very recently, so other outbursts may have been missed. The delta-Aurigids produce lower rates of generally fainter meteors, and have yet to be well-seen in more than an occasional year. 1997 provides a fine opportunity to improve our knowledge of the showers, since new Moon on September 2 means dark skies will prevail for much of the night for both maxima. Telescopic data to confirm the radiants -- and possibly observe the telescopic beta-Cassiopeids simultaneously -- would be especially useful, but photographs, video records and visual plotting would be welcomed too. The shower radiants are at a useful elevation from roughly 23h-00h onwards, so protracted watching is distinctly possible.
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, but before then we have the Orionids (whose central peak of several submaxima, October 21d 07h UT, is badly affected by a waning gibbous Moon, as are the minor epsilon-Geminids). Around October 9d 17h UT, any Draconid activity this year might be detected, when the Moon is at first quarter, but it is likely to be 1998, when Comet 21P/Giacobini-Zinner returns to perihelion, that we have the best chance to see any noticeable activity from this source. The Leonids (maximum due November 17, 15h UT) and the Geminids (peak: December 13, 22h UT) both lose out to bright moonlight in 1997, along with several of the late-year low-activity showers, such as the alpha-Monocerotids (those checking for another outburst at the time of 1995's should be alert around November 21d 13h UT), Monocerotids, sigma-Hydrids and Coma Berenicids. By contrast, the chi-Orionids, Phoenicids, the early part of the weak Puppid-Velid complex and Ursids during December are all rather better-placed with regard to the Moon.
Taurids
Southern Taurids
Active : October 1-November 25; Maximum : November 5 (lambda = 223°); ZHR = 5; Radiant : alpha = 050°, delta = +13°; Radiant drift: see Table 3; size : alpha = 20° x delta = 10°; V = 27 km/s; r = 2.3; TFC : Choose fields on the ecliptic and around 10° E or W of the radiants (beta>40° S).
Northern Taurids
Active : October 1-November 25; Maximum : November 12 (lambda = 230°); ZHR = 5; Radiant : alpha = 058°, delta = +22°; Radiant drift: see Table 3; size : alpha = 20° x delta = 10°; V = 29 km/s; r = 2.3; TFC : Choose fields on the ecliptic and around 10° E or W of the radiants (beta>40° S). Figure 14: Radiant position of the Northern and Southern TauridsThese two streams forms a complex associated with Comet 2P/Encke. Defining their radiants is best achieved by careful visual or telescopic plotting, photography or video work, since they are large and diffuse. The brightness and relative slowness of many shower meteors makes them ideal targets for photography, while these factors coupled with low, steady combined Taurid rates makes them excellent targets for newcomers to practice their plotting techniques on. The activity of both streams produces an apparently plateau- like maximum for about ten days in early November, and the shower has a reputation for producing some superbly bright fireballs at times, although seemingly not in every year. 1995 produced an impressive crop of brilliant Taurids between late October and mid-November, for instance, and the last few days of October with the opening ones of November seem especially likely to yield Taurid fireballs, from past analyses. New Moon on October 31 means this period, and the Southern Taurid maximum are notably favoured with dark skies in 1997. The near-ecliptic radiants for both shower branches mean all meteoricists can observe the streams, with the northern hemisphere somewhat better- placed, from where suitable radiant zenith distances obtain for much of the lengthening late autumnal nights. Even in the southern hemisphere, a good 3-5 hours' watching around local midnight is possible with Taurus well above the horizon, however.
chi-Orionids
Active : November 26-December 15; Maximum : December 2, (lambda = 250), ZHR = 3; Radiant : alpha = 082°, delta = +23°; Radiant drift: see Table 3; radius : 8°; V = 28 km/s; r = 3.0; TFC : alpha = 083°, delta = +09° and alpha = 080°, delta = +24° (beta>30° S). Figure 15: Radiant position of the chi-OrionidsThis weak visual stream is moderately active telescopically, although a number of brighter meteors have been recorded by professional photographic patrols in the past too. The shower has a double radiant (at least), but the southern branch has been rarely detected. The chi-Orionids may be a continuation of the ecliptic complex after the Taurids cease to be active. The radiant used here is a combined one, suitable for visual work, although telescopic or video observations should be better-able to determine the exact radiant structure. November's new Moon favours the shower with dark skies this year, and the radiant, actually in eastern Taurus at the shower's peak, is well on display for all watchers throughout the night.
Phoenicids
Active : November 28-December 9; Maximum : December 6, 08h UT (lambda = 254.25°); ZHR = variable, usually 3 or less, may reach 100; Radiant : alpha = 018°, delta = -53°; Radiant drift: see Table 3; radius : 5°; V = 18 km/s; r = 2.8; TFC : alpha = 040°, delta = 39° and alpha = 065°, delta = 62° (beta<10° N). Figure 16: Radiant position of the PhoenicidsOnly one impressive Phoenicid return has so far been reported, that of its discovery in 1956, when the ZHR was around 100. Three other potential bursts of lower activity have been reported, but never by more than one observer, under uncertain circumstances. IMO observers noted rates barely at the visual detection limit between 1988-1995, making the normal current activity virtually nonexistent. This may be a periodic shower, however, and more observations of it are needed by all methods. Radio workers may find difficulties, as radar echoes from the 1956 event were only 30 per hour, perhaps because these low-velocity meteors produce too little radio- reflecting ionization. Observing conditions this year are reasonable for all southern hemisphere watchers, with a waxing crescent Moon a problem only in the evening hours. This is a little unfortunate, since the radiant, although well on view for most of the night, culminates at dusk, but it should not be regarded as a major deterrent.
Ursids
Active : December 17-26; Maximum : December 22, 11h 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 = 063°, delta = +84° and alpha = 156°, delta = +64° (beta 30° to 40° N); Figure 17: Radiant position of the UrsidsA northern hemisphere shower which has been very poorly-observed, although at least two major outbursts have occurred in the past half-century or so, in 1945 and 1986, and 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. Its 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 waning Moon, just past last quarter, will be a minor nuisance this year when the radiant is approaching its highest, but with observations at a premium, that should not put off prospective watchers.
Abbreviations
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 2000.0. 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.
Tables
Table 1: Lunar phases for 1997. New First Full Last Moon Quarter Moon Quarter January 2 January 9 January 15 January 23 January 31 February 7 February 14 February 22 March 2 March 9 March 16 March 24 March 31 April 7 April 14 April 22 April 30 May 6 May 14 May 22 May 29 June 5 June 13 June 20 June 27 July 4 July 12 July 20 July 26 August 3 August 11 August 18 August 25 September 2 September 10 September 16 September 23 October 1 October 9 October 16 October 23 October 31 November 7 November 14 November 22 November 30 December 7 December 14 December 21 December 29 Table 2: Working list of visual meteor showers. Details in this Table correct according to the best information available in April 1996. 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 19)(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 12 139.6 046 +58 kappa-Cygnids Aug 03-Aug 25 Aug 17 145 286 +59 Northern iota-Aquarids Aug 11-Aug 31 Aug 19 147 327 -06 alpha-Aurigids Aug 25-Sep 05 Aug 31 158.6 084 +42 delta-Aurigids Sep 05-Oct 10 Sep 08 166 060 +47 Piscids Sep 01-Sep 30 Sep 19 177 005 -01 Draconids Oct 06-Oct 10 Oct 09 196.49 262 +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 17 235.16 153 +22 alpha-Monocerotids Nov 15-Nov 25 Nov 21 239.32 110 +03 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 08 257 100 +08 sigma-Hydrids Dec 03-Dec 15 Dec 11 260 127 +02 Geminids Dec 07-Dec 17 Dec 13 262.0 112 +33 Coma Berenicids Dec 12-Jan 23 Dec 19 268 175 +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 2.6 200 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 2.6 110 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 +23 113 -5 Nov 20 067 +24 064 +16 XOR 153 +21 117 -6 Nov 25 072 +24 069 +17 075 +23 121 -7 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
Useful addresses
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
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)
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!