IMO Meteor Shower Calendar 2007

Introduction

Welcome to the 2007 International Meteor Organization (IMO) Meteor Shower Calendar. The year looks set to be one of two unequal parts, with chiefly poorly-placed shower peaks through to the end of July, then a lot of virtually moonless shower maxima till mid December. The major Perseids and Geminids come off especially well, along with the possible Draconid epoch and Orionid maximum in October, the Taurids and Leonids in November, and most of the cluster of minor showers in early December. Of the stronger showers, the main lunar casualties are the Quadrantids, η-Aquarids, Southern δ-Aquarids and Ursids. While monitoring meteor activity should ideally be carried on throughout the year, we appreciate that this is not practical for many people, so this Calendar was first devised back in 1991 as a means of helping observers deal with reality by highlighting times when a particular effort might most usefully be employed. Although we include timing predictions for all the more active night-time and daytime shower maxima, based on the best available data, it is essential to realise that in many cases, such maxima are not known more precisely than to the nearest of solar longitude (even less accurately for the daytime radio showers, which have only recently begun to receive regular attention again). 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, still-imaging, telescopic, video and visual 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 (see Table 5), thanks to regular updating from 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 imaging, radar or telescopic 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 still-imaging techniques remain popular for nightly meteor coverage (weather permitting), although both suffer considerably from the presence of moonlight. Telescopic observations are much less popular, but 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 continue to be dynamically applied, and are increasingly bearing considerable fruit. These have the advantages, and disadvantages, of both still-imaging and telescopic observing, plus some of their own, but are increasing in importance. Radio receivers can be utilized at all times (suitable transmitters permitting!), 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 imaging 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

Full Moon wrecks the northern-hemisphere Quadrantids in early January (maximum due around 0h30m UT on January 4), while the waning gibbous Moon does much the same in the southern hemisphere for the probable α-Centaurid peak, expected near 11h UT on February 8. The minor, late February's δ-Leonids should just escape the waxing Moon. The interesting late January to early February spell (during which several new, swift-meteor, minor showers, radiating from the Coma-Leo-Virgo area have been suggested in some recent years), falls well for the new and waxing Moon, giving dark skies for most of the, perhaps core, January 2027 period. Mid-March brings a rather poor minor γ- Normid return, perhaps with a peak around either March 14 or 17 (it has not been properly observed for many years, and even its current existence has been doubted in some quarters), which has a waning Moon. March 17 has the better conditions, the Moon then only two days from new, for anyone wishing to check on this possible source. Theoretical approximate timings for the daytime radio shower maxima this quarter are: Capricornids/Sagittarids — February 1, 20h UT; and χ-Capricornids — February 13, 22h UT. Recent radio results suggest the Cap/Sgr maximum may variably fall sometime between February 14 however, while activity near the expected χ- Capricornid peak has tended to be slight and up to a day late. Both showers have radiants < 10°15° west of the Sun at maximum, so cannot be regarded as visual targets even from the southern hemisphere.

Antihelion Source (ANT)

Active:January 1 —December 31; interrupted by NTA/STA
Maximum:none;
ZHR = 3
Radiant drift: see Table 6
v = 30 km/s
r ~3

The revised Working List of Visual Meteor Showers as included in this Calendar does not list individual periods for various ecliptical showers, but combines them into a year-round source with a radiant drift as given in Table 6.

The Antihelion Source in January produces predominantly faint meteors and is well-suited to telescopic observations, with a large, complex, diffuse radiant that probably consists of several sub-centres. Visual observers should assume a minimum radiant size of roughly 20° in α by 10° in δ about the radiant point given in the above graph. Observations submitted to the IMO over the last decade have suggested an activity maximum may occur close to λ = 297° (2007 January 17), though ZHRs do not rise above ~ 34 even then. New Moon on January 19 makes the possible peak nicely moonless, and watches throughout this period to see what takes place should definitely be attempted. The long northern winter nights are ideal for making observations, while the radiant is above the horizon almost all night in either hemisphere.

δ-Leonids (DLE)

Active: February 15 —March 10
Maximum: February 25 (λ = 336°)
ZHR = 2
Radiant: α = 168°; δ = +16°
Radiant drift: see Table 6
v = 23 km/s
r = 3.0
TFC: α = 140°; δ = +37° and
α = 151°; δ = +22° (β > 10° N)
α = 140°; δ = -10° and
α = 160°; δ = +00° (β < 10° N)

This minor shower has a radiant very close to the Antihelion radiant, but has been found well separated in position and is probably linked with Asteroid (4450) Pan. These facts make the δ-Leonids an interesting source for meteor astronomy. 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 Antihelion meteors and the sporadics. Northern hemisphere sites have an advantage for covering this shower, though southern hemisphere watchers should not ignore it, as they are better-placed to note many of the possible Antihelion sub-radiants. On the peak night, the waxing gibbous Moon sets far enough from dawn north of the equator to allow a couple of hours' dark-sky watching at least, though the mid-southern hemisphere has a distinct advantage, with moonset around local midnight. The δ-Leonid radiant is well on view for most of the night then.

April to June

Meteor activity picks up towards the April-May boundary, with shower peaks from the Lyrids and π-Puppids in late April, then the badly moonlit η-Aquarids in early May (peak due at about 12h UT on May 6), and the η-Lyrids — a shower new to the Working List — with a peak on May 9, 12h. Later in May and throughout June, most of the meteor action switches to the day sky, with six shower maxima expected during this time. Although occasional meteors from the o- Cetids and Arietids have been claimed as seen from tropical and southern hemisphere sites visually in past years, ZHRs cannot be sensibly calculated from such observations. For radio observers, the theoretical UT peaks for these showers are as follows: April Piscids — April 20, 21h; δ-Piscids — April 24, 21h; ε- Arietids — May 9, 20h; May Arietids — May 16, 21h; o-Cetids — May 20, 19h; Arietids — June 7, 23h; \zeta-Perseids — June 9, 22h; β-Taurids — June 28, 21h. Signs of most of these were found in radio data from 19942005, though some are difficult to define individually because of their proximity to other radiants, while the Arietid and \zeta-Perseid maxima tend to blend into one another, producing a strong radio signature for several days in early to mid June. There are indications these two shower maxima now each occur up to a day later than indicated here too. The visual Antihelion Source continues with positions in Libra up to the end of April, in Scorpius and Ophiuchus in May, and in Sagittarius in June. The motion of the center of the radiant complex is given in the following two Figures. For northern observers, circumstances for checking on any potential June Lyrids are very favourable this year, albeit not so positive for possible June Boötid hunting.

Lyrids (LYR)

Active: April 1625
Maximum: April 22; 22h30m UT (λ = 32°32; but may vary — see text)
ZHR = 18 (can be variable - up to 90)
Radiant: α = 271°; δ = +34°
Radiant drift: see Table 6
v = 49 km/s
r = 2.1
TFC: α = 262°; δ = +16° and
α = 282°; δ = +19° (β > 10° S)

The λ = 32°32 timing given above was the “ideal” maximum time found in the most detailed examination of the Lyrids in modern times, published in 2001 by Audrius Dubietis and Rainer Arlt, drawing on IMO results from 19882000. However, the maximum time was found to be variable from year to year between λ = 32°032°45 (equivalent to 2007 April 22, 14h45m to April 23, 1h45m UT). Activity was discovered to be variable too. A peak at the ideal time produced the highest ZHRs, ~ 23, while the further the peak happened from this, the lower the ZHRs were, down to ~ 14. (The last very high maximum occurred outside the examined interval, in 1982 over the USA, when a short-lived ZHR of 90 was recorded.) The mean peak ZHR was 18 over the thirteen years examined. While generally thought of as having a short, quite sharp, maximum, this latest work revealed the shower's peak length was inconstant too. Using the interval that ZHRs were above half the maximum amount, the Full-Width-Half-Maximum time, a variation of from 15 hours (in 1993) to 62 hours (in 2000) was detected, with a mean value of 32 hours. The very best rates are normally achieved for just a few hours however. One other aspect of the analysis confirmed data from earlier in the 20th century, that occasionally, as their highest rates occurred, the Lyrids produced a short-lived increase of fainter meteors. Overall, the unpredictability of the shower in any given year always makes the Lyrids worth watching, since we cannot say when the next unusual return may take place.

Lyrids are best viewed from the northern hemisphere, but they are visible from many sites north and south of the equator, and the shower is suitable for all forms of observation. As its radiant rises during the night, watches can be usefully carried out from about 22h30m local time onwards from mid- northern sites, but only from well after midnight from the mid-southern hemisphere. The waxing Moon, at first quarter on April 24, sets between roughly local midnight and 1 a.m. for mid-northern sites on April 22, giving several hours of darker skies for observers between moonset and the start of morning twilight (sites further north have a progressively shorter useful observing interval). For the mid-southern hemisphere, the Moon sets much earlier in mid evening, so dark skies will prevail while the radiant is above the horizon. If the ideal maximum time recurs, it should be best-seen from sites in Europe and most of (particularly North) Africa eastwards to central Asia, but other maximum times are perfectly possible, as noted above.

π-Puppids (PPU)

Active: April 1528
Maximum: April 24; 3h40m UT (λ = 33°5)
ZHR = periodic - up to around 40
Radiant: α = 110°; δ = -45°
Radiant drift: see Table 6
v = 18 km/s
r = 2.0
TFC: α = 135°; δ = -55° and
α = 105°; δ = -25° (β < 20° N)

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 reached perihelion last in 2002 November, but nothing significant was detected from this source in 2003 April. The comet's next perihelion passage is in 2008 March, which may make that year's π-Puppids potentially more interesting. Activity this year may be unlikely, but regular monitoring of the shower epoch in future is vital, as coverage has commonly been patchy, and short-lived maxima could have been missed in the past.

The π-Puppids are best-seen from the southern hemisphere, with useful observations mainly practical there before midnight, as the radiant is very low to setting after 1h local time. On April 24, first quarter Moon sets around local midnight from such locations in 2007, leaving a short viewing window under dark skies. Well-placed sites combining darker skies with the radiant's visibility are likely to be in South America, if the maximum time proves correct. So far, visual and radio data have been collected on the shower, but the slow, bright nature of the meteors makes them ideal subjects for imaging too. No telescopic or video data have been reported in any detail as yet.

June Lyrids (JLY)

Active: June 1121
Maximum: June 16 (λ = 85°)
ZHR = variable - 05
Radiant: June 10: α = 273°; δ = +35°
June 15: α = 277°; δ = +35°
June 20: α = 281°; δ = +35°
v = 31 km/s;
r = 3.0.

This possible source does not feature in the current IMO Working List of Visual Meteor Showers, as apart from some activity seen from northern hemisphere sites in a few years during the 1960s (first seen 1966) and 1970s, evidence for its existence has been virtually zero since. In 1996, several observers independently reported some June Lyrids, though no definite activity has been found subsequently. The probable maximum date in 2007 has a virtually new Moon, yielding perfect viewing conditions for all observers who wish to check for this potential shower. The radiant may well lie a few degrees south of the bright star Vega (α Lyrae), so would be well on-view throughout the short northern summer nights, but there are discrepancies in its position in the literature. All suspected June Lyrids should be carefully plotted, paying especial attention to the meteors' apparent velocities. Confirmation or denial of activity from this source by imaging techniques would be very useful too.

June Boötids (JBO)

Active: June 22 —July 2
Maximum: June 27; 20h00m UT (λ = 95°7)
ZHR = variable - 0—100+
Radiant: α = 224°; δ = +48°
Radiant drift: see Table 6
v = 18 km/s
r = 2.2
TFC: α = 156°; δ = +64° and
α = 289°; δ = +67° (β = 25°60° N)

This source was reinstated on the Working List of Visual Meteor Showers after its unexpected return in 1998, when ZHRs of 50 —100+ were visible for more than half a day. A further outburst of similar length, but with ZHRs of ~ 2050 was observed on 2004 June 23, a date before definite activity had previously been recorded from this shower. We encourage all observers to routinely monitor the expected activity period, in case of future outbursts. Prior to 1998, only two definite returns had been detected, in 1916 and 1927, and with no significant reports between 19281997, it seemed probable these meteoroids no longer encountered Earth. The dynamics of the stream were poorly understood, although recent theoretical modelling has improved our comprehension. The shower's parent Comet 7P/Pons-Winnecke has an orbit that now lies around 0.24 astronomical units outside the Earth's at its closest approach. It was last at perihelion in 2002, and is next due in late 2008. Consequently, the 1998 and 2004 returns resulted from material shed by the comet in the past, and which now lies on slightly different orbits to the comet itself. Dust trails laid down at various perihelion returns during the 19th century seem to have been responsible for the last two main outbursts. There were no predictions in force for possible activity in 2007 at the time of writing, but the approach of June's second full Moon on the 30th will create problems for observations of the 1998 repeat time anyway (given above). Moonset between 1h2h local time will allow a short — in some areas very short! — darker-sky interlude for those mid-northern places where all-night twilight does not occur in June, as from here, the radiant is at a useful elevation for most of the short summer nights. All observing techniques can be employed.

July to September

The Antihelion low activity source is complemented by various radiants in the Cap/Aqr region until mid-August. Full Moon ruins all the late-July peaks from these, including the Piscis Austrinids (due on July 28), Southern δ-Aquarids (around July 2830) and α-Capricornids (circa July 3031). The best of the major Perseids comes with a new Moon, whose subsequent waning crescent favours the minor κ-Cygnid peak. In early September, the α-Aurigid maximum (due near 12h30m UT on September 1) is lost to the waning gibbous Moon, but the minor September Perseid peak is far more visible. For daylight radio observers, the interest of May-June has waned, but there remain the visually-impossible γ- Leonids (peak towards August 25, 21h UT, albeit not found in recent radio results), and a tricky visual shower, the Sextantids. Their maximum is expected on September 27, 22h UT, but may possibly occur a day earlier. In 1999 a strong return was detected at λ ~ 186°, equivalent to 2007 September 29, while in 2002, the September 27 peak was not found, but one around September 2930 was! It seems plausible that several minor maxima in early October may also be due to this radio shower. Full Moon creates additional difficulties for visual observers hoping to catch some Sextantids in late September, tricky enough with radiant-rise less than an hour before dawn in either hemisphere.

Aquarids and Capricornids

Southern δ-Aquarids (SDA)

Active: July 12 —August 19
Maximum: July 28 (λ = 125°)
ZHR = 20
Radiant: α = 339°; δ = -16°
Radiant drift: see Table 6
v = 41 km/s
r = 3.2
TFC: α = 255° to 000°; δ = 00° to +15°
choose pairs separated by about 30° in α (β < 40° N)

α-Capricornids (CAP)

Active: Jul 3 —August 15
Maximum: July 30 (λ = 127°)
ZHR = 4
Radiant: α = 307°; δ = -10°
Radiant drift: see Table 6
v = 23 km/s
r = 2.5
TFC: α = 255° to 000°; δ = 00° to +15°
choose pairs separated by about 30° in α (β < 40° N)
PFC: α = 300°; δ = +10° (β > 45° N
α = 320°; δ = -05° (β  0° to 45° N)
α = 300°; δ = -25° (β < 0°)

Fresh investigations of the near-ecliptic Aquarid and α- Capricornid (CAP) streams using IMO and other visual and video data have been published in recent years. These have generally confirmed the known details for the stronger Southern δ-Aquarid (SDA) and CAP maxima, but the SIA and NIA did not appear at all clearly, unsurprising given their borderline- visible ZHRs. The greatest oddity was the NDA, for which no distinct maximum could be traced, and whose ZHRs were never better than ~ 3. A recent investigation of the ecliptical radiants showed that what was regarded as the NDA radiant is in fact entirely within the radiant area of the Antihelion Source (radiant motion on page 13). The showers SIA, NIA, and NDA are no longer included in the new Working List for 2007.

Excepting the moonlit CAP, the Antihelion Source and SDA are rich in faint meteors, making them well-suited to telescopic work, although enough brighter members exist to make visual and imaging observations worth the effort too, primarily from more southerly sites. Radio work can be used to pick up the SDA especially, as the most active source, and indeed the shower can sometimes give a surprisingly strong radio signature. Such a concentration of radiants in a small area of sky makes for problems in accurate shower association. Visual watchers in particular should plot all potential shower members, rather than trying to make shower associations in the field. All SDA, CAP and ANT radiants are above the horizon for much of the night, with the fewest moonlight problems in the period of about August 8 —24.

Perseids (PER)

Active: July 17 —August 24
Maximum: August 13; 5h7h30m UT (λ = 140°0140°1) - but see text
ZHR = 100
Radiant: α = 046°; δ = +58°
Radiant drift: see Table 6
v = 59 km/s; r = 2.6
TFC: α = 019°; δ = +38° and
α = 348°; δ = +74° before 2h local time
α = 043°; δ = +38° and
α = 073°; δ = +66° after 2h local time (β > 20° N)
IFC: α = 300°; δ = +40°; α = 000°; δ = +20° or
α = 240°; δ = +70° (β > 20° N)

The Perseids were one of the most exciting and dynamic meteor showers during the 1990s, with outbursts at a new primary maximum producing EZHRs of 400+ in 1991 and 1992. Rates from this peak decreased to ~ 100120 by the late 1990s, and in 2000, it first failed to appear. This was not unexpected, as the outbursts and the primary maximum (which was not noticed before 1988), were associated with the perihelion passage of the Perseids' parent comet 109P/Swift-Tuttle in 1992. The comet's orbital period is about 130 years, so it is now receding back into the outer Solar System, and theory predicts that such outburst rates should dwindle as the comet to Earth distance increases. However, some predictions suggested 20042006 might bring a return of enhanced rates ahead of the usual maximum, and in 2004 a short, strong peak happened close to that anticipated pre-peak time. After that, activity seemed to be roughly normal in 2005, and the moonlit 2006 return was still to come when this text was prepared, but nothing untoward was predicted for 2007 in any case. An average annual shift of +0°05 in the λ of the “old” primary peak had been deduced from 199199 data, and allowing for this could give a possible recurrence time around 9h UT on August 13 (λ = 140°16), if so a little after the most probable maximum, that of the “traditional” peak always previously found, which is given above. Another feature, seen only in IMO data from 199799, was a tertiary peak at λ = 140°4, the repeat time for which would be 15h UT on August 13. Observers should be aware that these predictions may not be an absolute guide to the best from the Perseids, and plan their efforts accordingly, so as not to miss out, just in case!

Whatever happens, and whenever the peak or peaks fall around August 13, new Moon on August 12 creates perfect observing circumstances this year. For mid-northern latitudes, the radiant is sensibly observable from 22h23h local time onwards, gaining altitude throughout the night. The UT morning-hour maxima suggested here would be best-viewed from across North America and northern South America, while the possible ~ 15h UT peak would fall best for Far Eastern Asia.

Visual and still-imaging observers should need little encouragement to cover this stream, but telescopic and video watching near the main peak would be valuable in confirming or clarifying the possibly multiple nature of the Perseid radiant, something not detectable visually. Recent video results have shown a very simple, single radiant structure certainly. Radio data would naturally enable early confirmation, or detection, of perhaps otherwise unobserved maxima, assuming more than one takes place, if the timings or weather conditions prove 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.

κ-Cygnids (KCG)

Active: August 325
Maximum: August 18 (λ = 145°)
ZHR = 3
Radiant: α = 286°; δ = +59°
Radiant drift: see Table 6
v = 25 km/s
r = 3.0
IFC: α = 330°; δ = +60° and
α = 300°; δ = +30° (β > 20° N)

The early-setting waxing crescent Moon poses no problems for covering the expected κ-Cygnid peak this year by northern hemisphere observers (the locations from which the shower is chiefly accessible). Its r- value suggests telescopic and video observers may benefit from its presence, but visual and still-imaging 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 needed on a shower that is often ignored in favour of the major Perseids during August.

September Perseids (SPE)

Active: September 5 —September 17
Maximum: September 9 (λ = 166°7)
ZHR = 5
Radiant: α = 060°; δ = +47°
Radiant drift: see Table 6
v = 64 km/s
r = 2.9
TFC: α = 052°; δ = +60°; α = 043°; δ = +39° and
α = 023°; δ = +41° (β > 10° S)

This essentially northern hemisphere shower appears to be part of a series of poorly observed sources with radiants in Aries, Perseus, Cassiopeia and Auriga, active from late August into October. British and Italian observers independently reported a possible new radiant in Aries during late August 1997 for example. Both this shower and the similarly located δ- Aurigids have recently been investigated by analysts Audrius Dubietis and Rainer Arlt, using IMO-standard data since 1986, and their parameters updated accordingly.

Of the two known Aurigid sources, the α-Aurigids (AUR) are the more active, with short unexpected bursts having given EZHRs of ~ 3040 in 1935, 1986 and 1994, although they have not been monitored regularly until very recently, so other outbursts may have been missed. Only three watchers in total covered the 1986 and 1994 outbursts, for instance!

The September Perseids and δ-Aurigids, whose activities and radiants effectively overlap one another, were combined into one source in the Working List up to 2006. Since the activity curves show evidence for two individual showers, we have split them into the September Perseids and δ-Aurigids in the Working List for 2007. Near September 17, activities of both showers are actually interfering, but it is not recommended to distinguish the showers as their individual radiants are not resolvable. The δ-Aurigid phase seems to give a weak maximum around λ = 181° (2007 September 24; ZHR ~ 3, r = 2.5), but its peak time is poorly defined and may occur as late as λ = 191° (2007 October 4).

Radiants in and near Auriga reach useful elevations after 23h0h local time for early autumn northern watchers. Consequently, the September Perseid peak on September 9 is favoured over the main α-Aurigid one, as the Moon is almost new for it. Telescopic data to check for other radiants in this region of sky — and possibly observe the telescopic β-Cassiopeids simultaneously — would be especially valuable, but imaging records and visual plotting would be welcomed, as always.

Antihelion Source (ANT) in September

Active: until September 25 when NTA/STA take over
Maximum: none
ZHR = 3
Radiant drift: see Table 6
v = 30 km/s
r~3

Audrius Dubietis carried out an examination of IMO data on the Piscids (now comprised by the definition of the Antihelion Source) between 19851999 in early 2001, which essentially confir