Meteor activity picks up towards the April-May boundary, with shower peaks
from the hopelessly moonlit Lyrids (between 2h30m and 13h30m UT on April 22,
probably stronger the nearer the peak falls to 10h30m UT) and π-Puppids
(around 15h30m UT on April 23). In early May, the η-
Aquarids are rather better-placed to the nearly-new Moon. 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 a few meteors from the
ο-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, 9h; δ-Piscids – April
24, 9h; ε-Arietids – May 9, 7h; May Arietids – May 16, 8h; ο-
Cetids – May 20, 7h; Arietids – June 7, 10h; ζ-Perseids – June 9, 10h;
β-Taurids – June 28, 9h. Signs of most of these peaks were found in radio
data from 1994-2002, though some are difficult to define because of their
proximity to other sources, while the Arietid and ζ-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 each 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, and
their probable peaks in May-June. For northern observers, checking for any June
Lyrids will be hampered by the waxing gibbous Moon near their possible maximum
on June 16, while the waning gibbous Moon makes June Boötid hunting equally
difficult near their prospective peak on June 27 (potentially within six hours
of 8h UT, if anything manifests at all). Further general details on both showers
were in the 2004 Meteor Shower Calendar.
η-Aquarids
Active : April 19-May 28; Maximum : May 5, 24h UT (sol = 45.45°); ZHR : 60 (periodically variable, ~ 40-85); Radiant : alpha = 338°, delta = -01°; Radiant drift: see Table 6; V : 66 km/s r : 2.4; TFC : alpha = 319°, delta = +10° and alpha = 321°, delta = -23° (beta < 20° S).
This 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. Some useful results
have come even from sites around 40°,N latitude in recent years however,
and occasional meteors have been reported from further north, but 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. While the radiant is still low, η-Aquarid
meteors tend to have very long paths, which can mean observers underestimate
the angular speeds of the meteors, so extra care is needed when making such
reports.
A relatively broad maximum, sometimes with a variable number of submaxima,
usually occurs in early May. Fresh IMO analyses in recent years, based on data
collected between 1984-2001, have shown that ZHRs are generally above 30 between
about May 3-10, and that the peak rates appear to be variable on a roughly 12-year
timescale. The next highest rates should fall towards 2008-2010, if this
Jupiter-influenced cycle is borne-out. Visual ZHRs should thus be around 50-60
in 2005, according to this idea. Whatever the case, the slim waning crescent
Moon on May 5-6 (new on May 8) will be only a minor distraction late in the
night for southern hemisphere viewers then. All forms of observing can be used
to study the shower, with radio work allowing activity to be followed even from
many northern latitude sites throughout the daylight morning hours. The radiant
culminates at about 8h local time.
[image:665]
Figure 4
– Radiant position of the η-Aquarids.