July to September 2005

July's new Moon brings dark skies for the minor Pegasids and July Phoenicids, along with the near-ecliptic low activity Sagittarids, which end in mid-July. The various Aquarid and α-Capricornid sources continue the near-ecliptic shower complex theme from then until August, after which come the Piscids throughout September (with their badly moonlit probable maximum around September 19). The two late-July better peaks, from the Southern δ-Aquarids and the α-Capricornids, have a waning Moon, but should still survive to view for southern observers especially, along with the minor Piscis Austrinids. Early August's new Moon is good news for the minor Southern ι-Aquarid and Northern δ-Aquarid maxima, and for the major Perseids. Conditions deteriorate after that, but only for the low-activity κ-Cygnid, and the very weak Northern ι-Aquarid peaks, on August 17 and perhaps August 19 respectively. Note the Northern ι-Aquarid maximum is poorly resolved. It may fall between sol = 148°-151°, August 21-24, according to IMO 1988- 95 results, or around sol = 147°, August 19, based on earlier data. Then both the α- and δ-Aurigid maxima in early September are splendidly Moon-free. For daylight radio observers, the interest of May-June has waned, but there remain the visually impossible γ-Leonids (peak towards August 25, 9h UT, albeit not found in recent radio results), and a tricky visual shower, the Sextantids. Their maximum is expected on September 27, 9h UT, but may possibly occur a day earlier. In 1999 a strong return was detected at sol ~ 186°, equivalent to 2005 September 29, while in 2002, the September 27 peak was not found, but one around September 29-30 was! There is currently some debate over whether several minor maxima in early October may also be due to this radio shower. The waning crescent Moon adds only slightly to the 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 anyway.

Pegasids

Active      : July 7-13;
Maximum     : July 9 (sol = 107.107°);
ZHR         : 3;
Radiant     : alpha = 340°, delta = +15°; Radiant drift: see Table 6;
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 5 - Radiant position of the Pegasids.

Monitoring this short-lived minor shower is never easy, as a few cloudy nights mean its loss for visual observers. The shower is best-seen in the second half of the night. Consequently, the waxing crescent Moon, setting by the mid to late evening hours on July 9-10, provides near-perfect conditions for observers north and south of the equator this year. The maximum ZHR is generally low, and swift, faint meteors can be expected, favouring telescopic observing.

July Phoenicids

Active      : July 10-16;
Maximum     : July 13 (sol = 111°);
ZHR         : variable 3-10;
Radiant     : alpha = 032°, delta = -48°; Radiant drift: see Table 6;
V           : 47 km/s
r           : 3.0;
TFC         : alpha = 041°, delta = -39° and alpha = 066°, delta = -62° (beta < 10° N).

This minor shower can be seen from the southern hemisphere, from where its radiant attains a reasonable elevation above the horizon after midnight. This is a useful year to watch it, since the waxing Moon sets between local midnight and 1h for typical southerly sites on July 13. Visual activity can be quite variable, and indeed it appears to be a richer radio meteor source (possibly also telescopically; more results are needed). The peak has not been well-observed for some considerable time. Recent years have brought maximum ZHRs of under 4, when the winter weather has allowed any coverage at all. More data would be very welcome!

Figure 6 - Radiant position of the July Phoenicids.

Piscis Austrinids and Aquarid/Capricornid Complex

Piscis Austrinids

Active      : July 15-August 10;
Maximum     : July 28 (sol = 125°);
ZHR         : 5;
Radiant     : alpha = 341°, delta = -30°; Radiant drift: see Table 6;
V           : 35 km/s
r           : 3.2;
TFC         : alpha = 255° to 000°, delta = 00° to +15°, choose pairs separated by about 30° in α (beta < 30°N).

Southern δ-Aquarids

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

α-Capricornids

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

Southern ι-Aquarids

Active      : July 25-August 15;
Maximum     : August 4 (sol = 132°);
ZHR         : 2;
Radiant     : alpha = 334°, delta = -15°; Radiant drift: see Table 6;
V           : 34 km/s
r           : 2.9;
TFC         : alpha = 255° to 000°, delta = 00° to +15°, choose pairs separated by about 30° in α (beta < 30°N).

Northern δ-Aquarids

Active      : July 15-August 25;
Maximum     : August 8 (sol = 136°);
ZHR         : 4;
Radiant     : alpha = 335°, delta = -05°; Radiant drift: see Table 6;
V           : 42 km/s
r           : 3.4;
TFC         : alpha = 255° to 000°, delta = 00° to +15°, choose pairs separated by about 30° in α (beta < 30°N).

Figure 7 - Radiant position of the Capricornids, Northern and Southern δ-Aquarids.

Figure 8 - Radiant position of the Northern and Southern ι-Aquarids and the Piscis Austrinids.

The Aquarids and Piscis Austrinids are all streams 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 δ-Aquarids especially, as the most active of these showers. The α-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 α-Capricornid ZHRs to ~10 was noted in 1995 by European IMO observers, although the Southern δ-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. Visual watchers in particular should plot any 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 δ- Aquarids are near their peak, as from southern hemisphere sites in particular, rates may become too high for accurate plotting.

In 2005, the early-rising last quarter to waning crescent Moon creates especial problems for northern observers hoping to cover the late July maxima, although southern hemisphere watchers enjoy a significantly later moonrise for the July 28 and 30 peaks. The very weak Southern ι-Aquarids are ideally- located near new Moon, and the Northern δ-Aquarids are very favourable too, leaving only the Northern ι-Aquarids to fend off full Moon at their ill-defined maximum. All these radiants are above the horizon for much of the night.

Perseids

Active      : July 17-August 24;
Maximum     : August 12, 17h-19h30m UT (sol = 140.140°-140dg1), but see text;
ZHR         : 100;
Radiant     : alpha = 046°, delta = +58°; Radiant drift: see Table 6;
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).

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 ~ 100-120 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.

An average annual shift of +0.05° in sol had been deduced from 1991-99 data, and allowing for this could give a possible primary peak time around 18h30m UT on August 12 (sol = 140dg06), if so within the most probable maximum time, that of the "traditional" peak always previously found, given above. Another feature, seen only in IMO data from 1997-99, was a tertiary peak at sol = 140dg4, the repeat time for which would be 3h UT on August 13. Some researchers commented several years ago that 2004-06 might see a return of the primary peak. No specific predictions for 2005 had been issued before this Shower Calendar was prepared, but any prepared subsequently should feature in the IMO's journal WGN or on the IMO-News e-mailing list, and observers need to be alert to this possibility.

Figure 9 - Radiant position of the Perseids.

Whatever happens, and whenever the peak or peaks fall around August 12, the waxing crescent Moon, just before first quarter, will set for mid-northern latitudes about the time the radiant is becoming sensibly observable, between 22h-23h local time. The radiant gains altitude throughout the night for these more favourable locations. The August 12 maxima timings would be best-viewed from a zone running from the Near East to east Asia, including Japan, although the later the peak occurs, the less favourable places east in this region would be. The August 13 timing would be visible from the extreme west of both Europe and North Africa westwards to the eastern seaboard of North America and northern South America, over the North Atlantic Ocean.

Visual and photographic 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.

α- and δ-Aurigids

α-Aurigids

Active      : August 25-September 8;
Maximum     : September 1, 0h UT (sol= 158.158°);
ZHR         : 7;
Radiant     : alpha = 84°, delta = +42°; Radiant drift: see Table 6;
V           : 66 km/s
r           : 2.6;
TFC         : alpha = 052°, delta = +60°; alpha = 043°, delta = +39° and 
              alpha = 023°, delta = +41° (beta > 10° S).

δ-Aurigids

Active      : September 5-October 10;
Maximum     : September 9 (sol = 166.166°);
ZHR         : 5;
Radiant     : alpha = 060°, delta = +47°; Radiant drift: see Table 6;
V           : 64 km/s
r           : 2.9;
TFC         : alpha = 052°, delta = +60°; alpha = 043°, delta = +39° and 
              alpha = 023°, delta = +41° (beta > 10° S).

Figure 10 - Radiant position of the α- and δ-Aurigids.

Both these essentially northern hemisphere showers are excellently placed to catch the best dark skies near September's new Moon this year, so every opportunity should be taken to secure more observations on them. They appear to be part of a series of poorly observed showers 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 Aurigid sources have recently been investigated by analysts Audrius Dubietis and Rainer Arlt, using IMO-standard data since 1986, and their known parameters updated accordingly.

The α-Aurigids are the more active, with short unexpected bursts having given EZHRs of ~ 30-40 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 δ-Aurigids probably represent a combination of two separate, but possibly related, minor sources, the September Perseids and δ-Aurigids, whose activities and radiants effectively overlap one another. The showers are probably not resolvable by visual watchers, who are advised to apply the parameters listed above, although these primarily derive from the "September Perseid" phase. The "δ-Aurigid" phase seems to give a weak maximum around sol = 181° (2005 September 23-24; rm ZHR ~ 3, r= 2.5).

Radiants for both main showers reach useful elevations after 23h-0h local time, thus the new to waxing crescent Moon creates ideal lunar circumstances, setting at worst by early to mid-evening around September 9. Conditions will be much less favourable for the possible September 23-24 peak however, with a waning gibbous Moon. Telescopic data to examine all the radiants in this region of sky - and possibly observe the telescopic β-Cassiopeids simultaneously - would be especially valuable, but photographs, video records and visual plotting would be welcomed too.