April to June 2004

Meteor activity picks up towards the April-May boundary, with shower peaks
from the moonless Lyrids and pi-Puppids. In early May, the eta-Aquarids are lost
to full Moon for their main broad maximum around May 5. Later in May and
throughout June, most of the meteor action switches to the daytime sky, with six
shower maxima expected during this time. Although a few meteors from the o-
Cetids and Arietids have been reported 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, 2h UT
delta-Piscids	April 24, 2h UT
epsilon-Arietids	May 9, 1h UT
May Arietids	May 16, 2h UT
o-Cetids	May 20, 1h UT
Arietids	June 7, 4h UT
zeta-Perseids	June 9, 1h UT
beta-Taurids	June 28, 3h UT

Signs of most of these peaks were found in radio data from 1994-2001, though
some are difficult to define because of their proximity to other sources, while
the Arietid and zeta-Perseid maxima tend to blend into one another, producing a
strong radio signature for several days in early June. There are indications
these two shower maxima now occur up to a day later than indicated here too. The
visual ecliptical complexes continue with some late Virginids up to mid April,
after which come the minor Sagittarids, with their probable peaks in May-June.
Checking for any possible June Lyrids will be very practical, and although the
waxing Moon makes June Bootid hunting difficult, it is very important this
year.

Lyrids

 

Active  : April 16-25;   
     Maximum  : April 22, 04h 10m UT (sol = 32.32° );   
     ZHR   = 18 (can be variable, up to 90);   
     Radiant  : alpha = 271° , delta = +34° ;   
     Radiant drift: see Table 6;   
     V   = 49 km/s;   
     r   = 2.9;   
     TFC   : alpha = 262° , delta = +16° and   
         alpha = 282° , delta = +19° (beta>10° S).   
        
     

Figure 3: Radiant position and drift of the Lyrids

Audrius Dubietis and Rainer Arlt published a detailed investigation of the
Lyrids in IMO results from 1988-2000 in 2001, the most detailed examination of
the shower in modern times. Several fresh features were found, the most
important of which was to redefine the maximum time as variable from year to
year between sol = 32.0° -32.45° (equivalent to 2004 April 21, 20h 20m
UT to April 22, 7h 20m UT), with an ideal time of sol = 32.32° . Although
the mean peak ZHR was 18 over the thirteen years, actual peak ZHRs varied
dependent on when the maximum time occurred. A peak at the ideal time produced
the highest ZHRs, 23, while the further the peak happened from this ideal, the
more the ZHRs were reduced, to as low as 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.) While generally thought of as having a short, quite
sharp, maximum, this latest work revealed the shower’s peak length was variable
too. This was measured by how long ZHRs were above half the maximum value, the
Full-Width-Half-Maximum (FWHM) time. It varied from 14.8 h in 1993 to 61.7 h in
2000, with a mean value of 32.1 h. Best rates are normally achieved for just a
few hours however. One other aspect found, confirming data from earlier in the
20th century was 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 occur.

The shower is best viewed from the northern hemisphere, but it is visible
from many sites north and south of the equator, and is suitable for all forms of
observation. As the shower’s radiant rises during the night, watches can be
usefully carried out from about 22h 30m local time onwards. The waxing crescent
Moon sets around or well before this time for mid-northern sites on April 21/22,
and still sooner further south, so gives no problems. The ideal maximum time, if
it recurs, would be best-seen from sites in and immediately adjacent to the
North Atlantic Ocean (between roughly longitudes 10° to 70° W). Other
maxmum times are perfectly feasible, as outlined earlier.

pi-Puppids

 

Active  : April 15-28;   
     Maximum  : April 23, 9h UT (sol = 33.5° );   
     ZHR   = periodic, up to around 40;   
     Radiant  : alpha = 110° , delta = -45° ;   
     Radiant drift: see Table 6;   
     V   = 18 km/s;   
     r   = 2.0;   
     TFC   : alpha = 135° , delta = -55° and   
         alpha = 105° , delta = -25° (beta<20° N).   
        
     

Figure 4: Radiant position and drift of the pi-Puppids

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 October 2002,
but no readily detectable rates were found in April 2003. However, regular
monitoring during the shower’s activity in future is vital, as coverage has
commonly been patchy, and short-lived showers could have been missed in the
past.

The pi-Puppids are best seen from the southern hemisphere, with useful
observations mainly practical before local midnight, as the radiant is very low
to setting after 1h local time. The waxing crescent Moon will be setting by
roughly 19h-20h local time from such locations on April 22/23, allowing plenty
of dark skies for watching. Well-placed sites are likely to be across the
Southern Pacific Ocean, including all of New Zealand and possibly the extreme
eastern part of Australia, 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 photographic subjects too. No telescopic or video
data have been reported in any detail as yet.

June Lyrids

 

Active  : June 11-21;   
     Maximum  : June 15 (sol = 85° );   
     ZHR   = variable, 0 - 5;   
     Radiant  : alpha = 278° , delta = +35° ;   
     Radiant drift: June 10 alpha = 273° , delta = +35° ,   
         June 15 alpha = 277° , delta = +35° ,   
         June 20 alpha = 281° , delta = +35° ;   
     V   = 31 km/s;   
     r   = 3.0;   
     

Figure 5: Radiant position and drift of the June Lyrids

This shower 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 in 2004 benefits from a nearly-new Moon
on June 15, and we urge all observers who can to cover this possible stream. The
radiant is a few degrees south of the bright star Vega (alpha Lyrae), so will be
well on-view throughout the short northern summer nights, but there are
discrepancies in its position in the literature. All potential June Lyrids
should be carefully plotted, paying especial attention to the meteors’ apparent
velocities. Confirmation or denial of activity from this source by photography
or video would be very useful too.

June Bootids

 

Active  : June 26-July 2;   
     Maximum  : June 27, 01h 45m UT (sol = 95.7° );   
     ZHR   = variable, 0 - 100;   
     Radiant  : alpha = 224° , delta = +47° ;   
     Radiant drift: see Table 6;   
     V   = 14 km/s;   
     r   = 2.2;   
     TFC   : alpha = 156° , delta = +64° and   
         alpha = 289° , delta = +67° (beta=25..60° N).   
        
     

Figure 6: Radiant position and drift of the June Bootids

Following the wholly unexpected strong return of this shower in 1998, when
ZHRs of 50-100+ were visible for more than half a day, we reintroduced this
source to the Working List of Visual Meteor Showers, and encourage all observers
to routinely monitor the expected activity period in case of future outbursts.
Prior to 1998, only three definite returns had been detected, in 1916, 1921 and
1927, and with no significant reports between 1928-1997, it seemed probable
these meteoroids no longer encountered Earth. The dynamics of the stream are
poorly understood, although recent theoretical modelling has attempted to
resolve this problem. The shower’s parent Comet 7P/Pons-Winnecke was at
perihelion in January 1996 and again in May 2002. Its orbit currently lies
around 0.24 astronomical units outside the Earth’s at its closest approach, so
the 1998 return probably resulted from material shed by the comet in the past
(the comet’s perihelion returns of 1819 and 1869, or 1825, have been suggested
as probable origin dates). A substantial part of these meteoroids are thought to
have become trapped in a mean-motion resonance with Jupiter, and presently are
in an Earth-intersecting orbit. Work by Juergen Rendtel indicates the Earth may
encounter potentially substantial June Bootid rates again in 2004 on June 27,
around 1h UT. Thus although the waxing gibbous Moon will be a nuisance on June
26-27, it will set between local midnight and 1h for mid-northern sites, and as
the radiant is at a useful elevation for most of the short summer night in the
northern hemisphere (only), every effort should be made to secure as much data
as possible. Remember too that other nights during the shower may also produce
unexpected activity, even if the anticipated peak does not appear, so please be
alert!