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標 題: 國際流星組織(IMO)1998年流星雨日曆
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International Meteor Organization
1998 Meteor Shower Calendar (Net-Version)
=========================================
compiled by Alastair McBeath
based on data in IMO Monograph No.2: Handbook for Visual Meteor Observers,
edited by Juergen Rendtel, Rainer Arlt and Alastair McBeath, IMO, 1995,
with additional contributions from Rainer Arlt, Marc de Lignie, Juergen
Rendtel and Paul Roggemans. Layout by Andre Knoefel.
Introduction
------------
Welcome to the 1998 International Meteor Organization (IMO) Meteor Shower
Calendar. This year promises to be an extremely interesting one, with most
major showers free from moonlight interference (except the eta-Aquarids and
Perseids), the prospect of a Draconid return in October, and a possible
meteor storm from the Leonids in November. Do not forget that monitoring of
meteor activity should ideally be carried on throughout the rest of the
year too, however! We appreciate that this is not practical for many
observers, and this Calendar was devised as a means of helping observers
deal with reality by highlighting times when a particular effort may most
usefully be employed. Although we include to-the-hour predictions for all
the more active night-time and daytime shower maxima, based on the best
available data, please note 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). 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,
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.
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 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 photographic techniques remain popular for nightly meteor
coverage (weather permitting), although both suffer considerably from the
presence of moonlight. Telescopic observations are 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
already increasing 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 opening quarter of the year brings several low activity showers,
including the first of the year's main diffuse ecliptical stream complexes,
the Virginids, active from late January to mid-April. Of the two better
showers, only the northern-hemisphere Quadrantids in early January are free
from moonlight. The other, the alpha-Centaurids, a sometimes good southern
hemisphere shower (maximum around February 7, 16h UT) is too close to full
Moon for non-radio observations. The minor delta-Cancrids in mid-January
lose out too to a bright Moon, along with the gamma-Normids in mid-March.
Daylight radio peaks are due from the Capricornids/Sagittarids around 13h
UT on February 1, and the chi-Capricornids on February 13, probably around
14h UT. Neither radio shower has been well-observed in recent times, and as
both have radiants under 10deg-15deg 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, 17h UT (lambda = 283.16deg);
ZHR = 120 (can vary around 60-200);
Radiant: = 230deg, = +49deg; Radiant drift: see Table 3;
Radius: 5deg at maximum; V = 41 km/s; r = 2.1 at maximum, but variable;
TFC: alpha = 242deg, delta = +75deg and
alpha = 198deg, delta = +40deg (beta > 40deg N);
PFC: before 00h local time alpha = 150deg, delta = +70deg;
after 00h local time alpha = 180deg, delta = +40deg and
alpha = 240deg, delta = +70deg (beta > 40deg N).
The year commences with a good return of the Quadrantids for northern
hemisphere observers, as the Moon will be a waxing crescent setting by the
local late evening hours of January 3. Since the shower's radiant is in
northern Bootes, it is circumpolar for many northern locations, but it
attains a useful elevation only after local midnight or so, and gets higher
towards morning twilight. The Moon will thus present no problems in 1998.
An interesting challenge is to try spotting the occasional long-pathed
shower member from the southern hemisphere around dawn, but sensible
Quadrantid 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, confirmed by radio results in
1996 and 1997, and a repeat of which time in 1998 would favour sites from
Alaska and the Northern Pacific islands to Far Eastern Siberia, China and
Japan. 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 may make
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 and video observations from January 1-5 would be
particularly welcomed by those investigating this topic, using the PFCs and
TFCs given above, along with telescopic and visual plotting results.
delta-Leonids
-------------
Active: February 15 - March 10; Maximum: February 24 (lambda = 336deg);
ZHR = 2;
Radiant: alpha = 168deg, delta = +16deg; Radiant drift: see Table 3;
Radius: 5deg; V = 23 km/s; r = 3.0;
TFC: alpha = 140deg, delta = +37deg and
alpha = 151deg, delta = +22deg (beta > 10deg N);
alpha = 140deg, delta = -10deg and
alpha = 160deg, delta = 00deg (beta < 10deg N).
This minor shower is probably part of the early Virginid activity. 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 Virginids
and the sporadics. Northern hemisphere sites have a distinct advantage for
covering this stream, whose radiant is well on view for most of the night
near the peak, close to the "Sickle" or "Head" of Leo, but southern
hemisphere watchers should not ignore it, as they are better-placed to note
many of the other Virginid radiants. With the Moon just two days before new
at the shower's maximum, conditions could scarcely be better for observing
it.
April to June
-------------
Meteor activity picks up towards the April-May boundary, with showers like
the Lyrids, p-Puppids and h-Aquarids, and only this latter source suffers
from moonlight this year. During May and June, most of the activity is in
the daytime sky, with six shower peaks expected during 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. For
radio observers, the expected UT maxima for these showers and the Moon-
affected h- Aquarids are as follows:
April Piscids -- April 20, 13h UT;
delta-Piscids -- April 24, 13h UT;
eta-Aquarids -- May 6, 04h UT;
epsilon-Arietids -- May 9, 12h UT;
May Arietids -- May 16, 13h UT;
o-Cetids -- May 20, 11h UT;
Arietids -- June 7, 15h UT;
zeta-Perseids -- June 9, 14h UT;
beta-Taurids -- June 28, 14h UT.
The ecliptical complexes continue with some
late Virginids and the best from the minor Sagittarids in May-June.
Lyrids
------
Active: April 16 - 25; Maximum: April 22, 10h UT (lambda = 32.1deg);
ZHR: 15 (can be variable, up to 90);
Radiant: alpha = 271deg, delta = +34deg ; Radiant drift: see Table 3;
Radius: 5deg; V = 49 km/s; r = 2.9;
TFC: alpha = 262deg, delta = +16deg and
alpha = 282deg, delta = +19deg (beta > 10deg S).
The Lyrids are best viewed from the northern hemisphere, but they are
observable from many sites either north or south of the equator, and are
suitable for all forms of observation. Maximum rates are usually attained
for only an hour or two at best, although in 1996, mean peak ZHRs of 15-20
persisted for around 8-12 hours. The ZHR can be rather erratic at times, a
variability also seen in 1996, when rates ranged between 10-30 from hour to
hour during the peak. The last high maximum occurred in 1982 over the USA,
when a very short-lived peak ZHR of 90 was recorded. This unpredictability
always makes the Lyrids a shower to watch, since we cannot say when the
next unusual return may occur.
As the shower's radiant rises during the night, watches can be usefully
carried out from about 22:30 local time onwards. This year, the Moon will
be a waning crescent in Capricornus/Aquarius for the peak, and will rise
not long before dawn, so skies should remain dark for much of the night.
The predicted maximum should favour sites across North America if correct,
but variations in the stream could mean this is not the case in actuality.
pi-Puppids
----------
Active: April 15 - 28; Maximum: April 23, 20h UT (lambda = 33.5deg);
ZHR: periodic, up to around 40;
Radiant: alpha = 110deg, delta = -45deg ; Radiant drift: see Table 3;
Radius: 5deg; V = 18 km/s; r = 2.0;
TFC: alpha = 135deg, delta = -55deg and
alpha = 105deg, delta = -25deg (beta < 20deg 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 was due
at perihelion on 1997 August 30, but in 1997 an almost full Moon coincided
with the shower's peak. At the 1998 return, we reach the closest-approach
point to the orbit almost eight months after the comet, so this will be a
useful year to check for pi-Puppid activity further from the comet,
especially as the Moon is just three days from new for the maximum.
The shower is best-seen from the southern hemisphere, with useful
observations mainly possible before local midnight, as the radiant is very
low or setting after 1h local time. 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 either.
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; the Southern iota-
Aquarid and Northern delta-Aquarid maxima lose out to August's full Moon),
and finally the Piscids into September. Other showers that vanish into
bright moonlight this quarter include the Pegasids and Phoenicids in July;
the Perseids in August (coverage is still important, but will be
exceptionally difficult with a waning gibbous Moon; the maxima are
predicted for August 12, 14h UT and August 12, 22h UT); and the alpha- and
delta-Aurigids in September (alpha-Aurigid peak due around September 1, 05h
UT). At least the minor kappa-Cygnids still survive this moonlight
onslaught! For daylight radio observations, the interest of May-June has
waned, but there remain the visually-inaccessible gamma-Leonids (peak due
August 25d 14h UT), and a tricky visual shower, the Sextantids (maximum
expected September 27d 14h UT). The latter has no problems from the waxing
crescent Moon, but its radiant will rise less than an hour before dawn
ineither hemisphere.
Piscis Austrinids and Aquarid/Capricornid Complex
-------------------------------------------------
Piscis Austrinids
-----------------
Active: July 15 - August 10; Maximum: July 28 (lambda = 125deg); ZHR = 5;
Radiant: alpha = 341deg, delta = -30deg; Radiant drift: see Table 3;
Radius: 5deg; V = 35 km/s; r = 3.2;
TFC: alpha = 255deg to 000deg, delta = 00deg to +15deg,
choose pairs separated by about 30deg in alpha (beta < 30deg N).
Southern delta-Aquarids
-----------------------
Active: July 12 - August 19; Maximum: July 28, 06h UT (lambda = 125deg);
ZHR = 20;
Radiant: alpha = 339deg, delta = -16deg; Radiant drift: see Table 3;
Radius: 5deg; V = 41 km/s; r = 3.2;
TFC: alpha = 255deg to 000deg, delta = 00deg to +15deg,
choose pairs separated by about 30deg in alpha (beta < 40deg N).
alpha-Capricornids
------------------
Active: July 3 - August 15; Maximum: July 30 (lambda = 127deg ); ZHR = 4;
Radiant: alpha = 307deg, delta = -10deg ; Radiant drift: see Table 3;
Radius: 8deg; V = 23 km/s; r = 2.5;
TFC: alpha = 255deg to 000deg, delta = 00deg to +15deg,
choose pairs separated by about 30deg in alpha (beta < 40deg N).
PFC: alpha = 300deg, delta = +10deg (beta > 45deg N),
alpha = 320deg, delta = -05deg (beta = 0deg to 45deg N),
alpha = 300deg, delta = -25deg (beta < 0deg S.)
Northern iota-Aquarids
----------------------
Active: August 11 - 31; Maximum: August 20 (lambda = 147deg); ZHR = 3;
Radiant: alpha = 327deg, delta = -06deg; Radiant drift: see Table 3;
Radius: 5deg; V = 31 km/s; r = 3.2;
TFC: alpha = 255deg to 000deg, delta = 00deg to +15deg,
choose pairs separated by about 30deg in alpha (beta < 40deg 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 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 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 observing nights. 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, as from southern
hemisphere sites in particular, rates may become too high for accurate
plotting.
All the above listed shower maxima are almost free from lunar interference
in 1998. The Piscis Austrinid, Southern delta-Aquarid and alpha-Capricornid
maxima have only a waxing crescent Moon to contend with, while August's new
Moon falls favourably for the Northern iota-Aquarid peak. All these
radiants are above the horizon for much of the night.
kappa-Cygnids
-------------
Active: August 3 - 25; Maximum: August 18 (lambda = 145deg); ZHR = 3;
Radiant: alpha = 286deg, delta = +59deg; Radiant drift: see Table 3;
Radius: 5deg; V = 25 km/s; r = 3.0;
TFC: alpha = 330deg, delta = +60deg and
alpha = 300deg, delta = +30deg (beta > 20deg N).
The waning crescent Moon will rise during the local early morning hours at
the kappa-Cygnid peak this year, a very minor nuisance only for watchers
north of the equator, where the shower is chiefly accessible from. Its r-
value suggests telescopic and video observers may benefit from its
presence, but visual and photographic 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 urgently needed on a shower that often is
ignored in favour of the Perseids during August.
Piscids
-------
Active: September 1 - 30; Maximum: September 20 (lambda = 177deg); ZHR = 3;
Radiant: alpha = 005deg , delta = -01deg; Radiant drift: see Table 3;
Radius: 5deg; V = 26 km/s; r = 3.0.
TFC: alpha = 340deg to 020deg, delta = -15deg to +15deg,
choose pairs separated by about 30deg in alpha (beta any).
The Piscids are a poorly-studied minor shower, with a radiant very close to
the March equinox point in the sky. Consequently, they can be studied
equally well from either hemisphere throughout the night near the September
equinox, close to their probable maximum time. This year, new Moon falls
exactly on September 20, but there is some doubt as to exactly when the
Piscid peak may occur - or indeed, if there is only the one. Telescopic and
video methods can be usefully employed to study it, along with careful
visual plotting.
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 (the Southern
Taurid maximum will be lost to bright moonlight this year, but something of
the Northern peak should still be seen). Before then come an important
return of the Draconids, the Orionid and the minor epsilon-Geminid maxima.
This is also a key year for the Leonids in November, and a good one to
check for a repeat of 1995's outburst for the alpha-Monocerotids.
December's full Moon claims the maxima of the chi-Orionids, Phoenicids
(December 6, 13h UT) and the early, better, part of the weak Puppid-Velid
complex, as well as much of the Monocerotids and sigma-Hydrids. This does
mean the Geminids, Coma Berenicids and Ursids are all much better-placed
with regard to the Moon.
Draconids
---------
Active: October 6 - 10; Maximum: October 8, 17-23h (lambda = 195.40deg);
ZHR = periodic, up to storm levels;
Radiant: alpha = 262deg, delta = +54deg; Radiant drift: negliginle;
Radius: 5deg; V = 20 km/s; r = 2.6;
TFC: alpha = 290deg, delta = +65deg and
alpha = 288deg, delta = +39deg (beta > 30deg N).
Despite the presence of a waning gibbous Moon, which will rise within 2-3
hours of nightfall for the northern hemisphere sites this shower is visible
from, 1998 is a very important year for observing the Draconids. This
periodic shower has produced spectacular, brief, meteor storms twice
already this century, in 1933 and 1946, and lower rates in several other
years (ZHRs around 20-200+), most recently in 1985. So far, detectable
activity has only been seen in years when the stream's parent comet,
21P/Giacobini-Zinner, has returned to perihelion, which it is expected to
do again in 1998 November. Perturbations of the stream, coupled with the
fact that the 1946 event remains the best-observed return, mean predicting
when activity might occur is very difficult. The spread in solar longitudes
at which notable past activity has been detected is from lambda = 195.26deg
(1985) to lambda = 197.0deg (1933), which equates to times between October
8, 17h UT and October 10, 12h UT in 1998. This is certainly a period that
all observers should be alert to, using a full range of techniques, but
with the Earth expected to pass the comet's node at lambda = 195.398deg
(October 8, 21 h UT), times earlier in this period may be more likely. The
peak time given in the box above is a mean value of the previous returns,
and should be viewed more as a general guide than an absolute value. The
radiant, near Draco's "Head", is circumpolar from many locations, but is
higher in the pre-midnight and near-dawn hours on October 8-10.
Photographic and video data would be especially valuable in case high rates
do take place.
epsilon-Geminids
----------------
Active: October 14 - 27; Maximum: October 18 (lambda = 205deg); ZHR = 2;
Radiant: alpha = 102deg, delta = +27deg; Radiant drift: see Table 3;
Radius: 5deg; V = 70 km/s; r = 3.0;
TFC: alpha = 090deg, delta = +20deg and
alpha = 125deg, delta = +20deg (beta > 20deg S).
A weak minor shower, whose meteors are very like the Orionids, active, and
at maximum, around the same time, so great care must be taken to separate
the two sources by instrumental techniques - especially video or telescopic
work - or visual plotting. New Moon on October 20 presents an excellent
opportunity to obtain more data on them from either hemisphere, although
northern observers have an advantage. The radiant is higher only after
midnight.
Orionids
--------
Active: October 2 - November 7; Maximum: October 21 (lambda = 208),
ZHR = 20;
Radiant: alpha = 095deg, delta = +16deg; Radiant drift: see Table 3;
Radius: 10deg; V = 66 km/s; r = 2.9;
TFC: alpha = 100deg, delta = +39deg and
alpha = 075deg, delta = +24deg (beta > 40deg N); or
alpha = 080deg, delta = +01deg and
alpha = 117deg, delta = +01deg (beta < 40deg N).
October's new Moon enhances the Orionids this year too. They are noted for
having several maxima other than the main one detailed above, with activity
sometimes remaining almost constant for several consecutive nights centred
on this peak. In 1993, a submaximum as strong as the normal peak was
detected on October 17-18 from Europe, for instance. All observers should
be aware of these possibilities. Several subradiants have been reported in
the past, but recent video work suggests the radiant is far less complex;
photographic, telescopic and video work to confirm this would be useful, as
visual observers have clearly had problems with this shower's radiant
determination before. With a radiant almost on the celestial equator, the
shower can be seen from most of the globe, and observations are possible
from midnight onwards in both hemispheres, perhaps a little before in the
north.
Leonids
-------
Active: November 14 - 21; Maximum: November 17, 19h UT (lambda = 235.25deg);
ZHR = 40+ (45 in 1996), but may reach storm levels in 1998-99;
Radiant: alpha = 153deg, delta = +22deg; Radiant drift: see Table 3;
Radius: 5deg; V = 71 km/s; r = 2.9;
TFC: alpha = 140deg, delta = +35deg and
alpha = 129deg, delta = +06deg (beta > 35deg N); or
alpha = 156deg, delta = -03deg and
alpha = 129deg, delta = +06deg (beta < 35deg N);
PFC: before 00h local time alpha = 120deg, delta = +40deg (beta > 40deg N);
before 04h local time alpha = 120deg, delta = +20deg (beta > 40deg N);
and after 04h local time alpha = 160deg, delta = 00deg (beta > 00deg N);
before 00h local time alpha = 120deg, delta = +10deg (beta > 40deg N);
and alpha = 160deg, delta = -10deg (beta < 00deg N).
The recovery of the Leonids' parent comet, 55P/Tempel-Tuttle, on 1997 March
4 has raised hopes further that a storm of Leonids might occur in 1998 or
1999. There are, of course, no guarantees that this will happen, but all
observers must realise that even discovering the absence of any unusual
Leonid activity would still be very valuable information - albeit not all
that interesting to witness! Visual IMO International Leonid Watch and
radio observations in 1996 indicated quite a broad Leonid maximum between
lambda = around 235.1deg-235.4deg (equivalent to 1998 November 17, 14h-22h
UT), with one minor peak at lambda = 235.17deg (1998 November 17, 17h UT).
As the Earth should pass the node of the comet's orbit around 1998
November 17, 19h UT (lambda = around 235.3deg), this may well be the most
likely time for the very highest activity to occur.
As the radiant, in Leo's "Head" or "Sickle" asterism, rises only around
local midnight (or indeed afterwards south of the equator), places in the
Far East, including China, Eastern Siberia and Japan, south through the
Western Pacific islands to Australia, should be the favoured spots, if the
maximum keeps to this time. Even a minor variation could mean places east
or west of this zone may see something of the shower's best too, however.
Look out for further updates in the IMO's journal WGN after the 1997
return. The Moon is just two days from new on November 17, so it will cause
no problems this year, and all observing methods should be utilised to the
full, especially photography and video if a storm manifests.
alpha-Monocerotids
------------------
Active: November 15 - 25; Maximum: November 21, 20h UT (lambda = 239.32deg);
ZHR = variable, usually around 5 but may produce outbursts to around 400+;
Radiant: alpha = 117deg, delta = +01deg; Radiant drift: see Table 3;
Radius: 5deg; V = 65 km/s; r = 2.4;
TFC: alpha = 115deg, delta = +23deg and
alpha = 129deg, delta = +20deg (beta > 20deg N);
alpha = 110deg, delta = -27deg and
alpha = 098deg, delta = +06deg (beta < 20deg N).
Another late-year shower capable of producing surprises, the alpha-
Monocerotids gave their most recent brief outburst in 1995 (the top EZHR,
around 420, lasted just five minutes; the entire outburst 30 minutes). Many
observers across Europe witnessed it, and we have been able to completely
update the known shower parameters as a result. Whether this indicates the
propsed ten-year periodicity in such returns is real or not, only the
future will tell, however, so all observers should continue to monitor this
source closely. New Moon on November 19 makes this an excellent year for
such scrutiny, with the radiant well on view in both hemispheres after
about 23h local time or so.
Geminids
--------
Active: December 7 - 17; Maximum: December 14, 05h UT (lambda = 262.0deg);
ZHR = 120;
Radiant: alpha = 112deg, delta = +33deg; Radiant drift: see Table 3;
Radius: 5deg; V = 35 km/s; r = 2.6;
TFC: before 23h local time alpha = 087deg, delta = +20deg and
alpha = 135deg, delta = +49deg;
after 23h local time alpha = 087deg, delta = +20deg and
alpha = 129deg, delta = +20deg (beta > 40deg N);
alpha = 120deg, delta = -03deg and
alpha = 084deg, delta = +10deg (beta < 40deg N);
PFC: alpha = 150deg, delta = +20deg and
alpha = 060deg, delta = +40deg (beta > 20deg N);
and alpha = 135deg, delta = -05deg and
alpha = 080deg, delta = 00deg (beta < 20deg N).
One of the finest annual showers presently observable, their early stages
will be lost to moonlight this year, but their peak occurs with a waning
crescent Moon which should present few problems, and then only late in the
night. Well north of the equator, the radiant rises around sunset, and can
be usefully observed from the local evening hours onwards, but in the
southern hemisphere, the radiant appears only around local midnight or so.
Even here, this is a splendid stream of often bright, medium-speed meteors,
a rewarding sight for all watchers. The peak has shown slight signs of
variability in its maximum rates and the actual peak timing (ZHRs were
around 110 around lambda 262.2deg-262.4deg in 1996, for instance), so the
best activity may occur a little before or after the suggested time above.
Even so, European, African, Near Eastern and American sites are the most
likely beneficiaries of the very best Geminid rates in 1998. Some mass-
sorting within the stream means the fainter telescopic meteors should be
most abundant almost 1deg of solar longitude ahead of the visual maximum,
with telescopic results indicating these meteors radiate from an elongated
region, perhaps with three sub-centers. Further results on this topic would
be useful, but all observing methods can be employed to observe the shower.
Coma Berenicids
---------------
Active: December 12 - January 23; Maximum: December 20, (lambda = 268deg);
ZHR = 5;
Radiant: alpha = 175deg, delta = +25deg; Radiant drift: see Table 3;
Radius: 5deg; V = 65 km/s; r = 3.0;
TFC: alpha = 180deg, delta = +50deg and alpha = 165deg, delta = +20deg
before 03h local time,
alpha = 195deg, delta = +10deg and alpha = 200deg, delta = +45deg
after 03h local time (beta > 20deg N).
A weak minor shower that is usually observed only during the Geminid and
Quadrantid epochs, but which needs more coverage at other times too,
especially to better-define its maximum. The shower is almost unobservable
from the southern hemisphere, so northern watchers must brave the winter
cold to improve our knowledge of it, especially this year as its expected
peak is just two days after new Moon. The radiant is at a useful elevation
from local midnight onwards.
Ursids
------
Active: December 17 - 26; Maximum: December 22, 18h UT (lambda = 270.7deg);
ZHR = 10 (occasionally variable up to 50);
Radiant: alpha = 217deg, delta = +76deg; Radiant drift: see Table 3;
Radius: 5deg; V = 33 km/s; r = 3.0;
TFC: alpha = 348deg, delta = +75deg and
alpha = 131deg, delta = +66deg (beta > 40deg N);
alpha = 063deg, delta = +84deg and
alpha = 156deg, delta = +64deg (beta 30deg to 40deg N);
A very poorly-observed northern hemisphere shower, but one which has
produced at least two major outbursts in the past half-century or so, in
1945 and 1986. 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. The radio maximum in 1996 occurred around
lambda 270.8deg, for instance, which might suggest a slightly later maximum
time in 1998 of December 22, 20h UT. The Ursid 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 waxing crescent Moon will give dark skies for observations almost all
night on December 22.
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 : The 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 are
given for the equinox J2000.0.
V : Pre-atmospheric or entry velocity of the meteoroid 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 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. Note that the TFCs are also
useful centres to use for video camera fields as well.
---------------------------------------------------------------------------
Table 1: Lunar phases for 1997.
New First Full Last
Moon Quarter Moon Quarter
January 5 January 12 January 20
January 28 February 3 February 11 February 19
February 26 March 5 March 13 March 21
March 28 April 3 April 11 April 19
April 26 May 3 May 11 May 19
May 25 June 2 June 10 June 17
June 24 July 1 July 9 July 16
July 23 July 31 August 8 August 14
August 22 August 30 September 6 September 13
September 20 September 28 October 5 October 12
October 20 October 28 November 4 November 11
November 19 November 27 December 3 December 10
December 18 December 26
---------------------------------------------------------------------------
---------------------------------------------------------------------------
Table 2: Working list of visual meteor showers. Details in this Table were
correct according to the best information available in June 1997. 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.
Activity Maximum Radiant
Shower Period Date lambda alpha delta
[deg] [deg] [deg]
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 06 045.5 338 -01
Sagittarids Apr 15-Jul 15 (May 20)(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 12 140.0 046 +58
kappa-Cygnids Aug 03-Aug 25 Aug 18 145 286 +59
Northern iota-Aquarids Aug 11-Aug 31 Aug 20 147 327 -06
alpha-Aurigids Aug 25-Sep 05 Sep 01 158.6 084 +42
delta-Aurigids Sep 05-Oct 10 Sep 08 166 060 +47
Piscids Sep 01-Sep 30 Sep 20 177 005 -01
Draconids Oct 06-Oct 10 Oct 08 195.4 262 +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 17 235.25 153 +22
alpha-Monocerotids Nov 15-Nov 25 Nov 21 239.32 117 +01
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 09 257 100 +08
sigma-Hydrids Dec 03-Dec 15 Dec 12 260 127 +02
Geminids Dec 07-Dec 17 Dec 14 262.0 112 +33
Coma Berenicids Dec 12-Jan 23 Dec 20 268 175 +25
Ursids Dec 17-Dec 26 Dec 22 270.7 217 +76
IMO
Shower v r ZHR Code
[km/s]
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 90 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 2.6 120 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 45deg 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 alp.del. 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 (FIDAC):
Andre Knoefel, Saarbruecker Strasse 8, D-40476 Duesseldorf, 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.
e-mail: radio@imo.net
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
or contact IMO's Homepage in the World-Wide-Web:
http://www.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!
(C) 1997 by International Meteor Organization