最新消息：
今天从meteorobs（IMO的讨论组）上收到了美国流星协会的Robert Lunsford
发表的世界时5月6日至5月12日的流星活动的细节预报和背景介绍：
Meteor Activity Outlook for May 6-12, 2005
This upcoming period will see the moon reaching its new phase on Sunday May
8. At this time the moon rises and sets with the sun and will out of the sky
all night long. As the week progresses the moon will enter the evening sky
as a thin waxing crescent but will still set before the active morning hours
arrive. The estimated total hourly rates for evening observers this week
should be near two for those in the Northern Hemisphere and three for those
observers south of the equator. For morning observers the estimated total
hourly rates should be near seventeen for those located in the Northern
Hemisphere and nineteen for those in the Southern Hemisphere. These rates
assume that you are watching from rural areas away from all sources of light
pollution. The actual rates will also depend on factors such as personal
light and motion perception, local weather conditions, alertness and
experience in watching meteor activity.
The radiant positions listed below are exact for Saturday night/Sunday
morning May 7/8. These positions do not change greatly day to day so the
listed coordinates may be used during this entire period. Most star atlases
(available at science stores and planetariums) will provide maps with grid
lines of the celestial coordinates so that you may find out exactly where
these positions are located in the sky. A planisphere or computer
planetarium program is also useful in showing the sky at any time of night
on any date of the year. Activity from each radiant is best seen when it is
positioned highest in the sky, either due north or south along the meridian,
depending on your latitude. Meteor activity is not seen from radiants that
are located below the horizon. The positions below are listed in a west to
east manner in order of right ascension (celestial longitude). The positions
listed first are located further west therefore are accessible earlier in
the night while those listed further down the list rise later in the night.
These are the showers that may be observed this week:
The Anthelion radiant is now centered at 16:08 (242) -20. This area of the
sky is located in northwestern Scorpius, just one degree south of the third
magnitude star Acrab (Beta Scorpii). These meteors were once called the
Alpha Scorpiids, as the radiant is located close to the bright orange star
this time of year. Since this radiant is large and diffuse, any slow to
medium speed meteor from eastern Libra, southwestern Ophiuchus or
northwestern Scorpius could be a candidate for this shower. The center of
this area is best placed near 0200 local daylight time when it lies on the
meridian and is highest in the sky. At this time expect to see two shower
members per hour no matter your location.
Unlike most of the annual showers the antihelion source is produced by
debris from unknown objects orbiting in a direct motion like the earth.
These objects are most likely asteroids, which produce stony and metallic
debris whose density is much greater than material produced by comets. There
is also the possibility that some of this activity may be caused by the
"Jupiter family of comets", comets which have been altered by Jupiter's
gravity into much shorter orbits. This material collides with the earth on
the inbound portion of its orbit, before its closest approach to the sun.
Therefore we best see them just after midnight when we are facing the
direction from which this activity appears. The antihelion source is active
all year from an area of the sky nearly opposite that of the sun. The center
of this source will move approximately one degree eastward per day and
travels through many different constellations over the course of a year. It
may make sense to list these meteors as anthelions or "ANT" but a majority
of meteor organizations prefer that you list them from the constellation in
which the radiant is currently located or the constellation where the shower
reaches maximum activity. Observers who send their reports to the
International Meteor Organization (I.M.O.) should label these meteors as
Sagittarids (SAG).
The Beta Corona Australids (CAU) are listed among the radiants of the Dutch
Meteor Society. The current radiant position is located at 18:16 (274) -41.
This area of the sky is located in western Corona Australis, seven degrees
northeast of the second magnitude star Sargas (Theta Scorpii). The best time
to view this activity is near 0400 local daylight time, when the radiant
lies highest in a dark sky. Rates at maximum activity (May 16) are only
three shower members per hour. Current rates would be less than one per
hour. Observers in the Southern Hemisphere have an advantage with the
radiant rising much higher in their sky. With an entry velocity of 45
kilometers per second, a majority of these meteors will appear to move at
moderate speeds.
The Eta Lyrids (IAA) are produced by comet IRAS-Araki-Alcock, which passed
very close to the Earth twenty two years ago this May. Weak activity from
this radiant has been seen in most years from May 5 through May 17, with
maximum activity occurring on May 9. The current radiant position is located
at 19:08 (287) +44. This area of the sky is located in northeastern Lyra,
five degrees northeast of the zero magnitude star Vega (Alpha Lyrae). The
best time to view this activity is just before the start of morning
twilight, when the radiant lies highest in a dark sky. With an entry
velocity of 44 kilometers per second, a majority of these meteors will
appear to move at moderate speeds.
宝瓶座η流星雨：
The Eta Aquarids (ETA) are particles from Halley's Comet, which last passed
through the inner solar system in 1986. Even though this is now nineteen
years ago, material is still encountered every year in late April and
throughout most of May. We passed closest to Halley's orbit on May 5.
Current rates should still be 10-15 per hour from a radiant located at 22:40
(340) -01. This area of the sky is located in northern Aquarius, one degree
southeast of the fourth magnitude star Eta Aquarii. The best time to view
this activity is just before the start of morning twilight, when the radiant
lies highest in a dark sky. Observers located closer to the tropics have a
better chance of seeing these meteors as the radiant will rise higher into a
dark sky. Morning twilight is especially troublesome in the high Northern
latitudes, where the radiant is situated low in the sky at the start of
twilight. With an entry velocity of 66 kilometers per second, a majority of
these meteors will appear to move swiftly and produce a high percentage of
persistent trains.
The Sporadic rates for the Northern Hemisphere are now reaching their low
plateau for the year. From now through June morning sporadic rates will
remain near five per hour. During the dark evening hours perhaps two random
meteors can be seen per hour. Sporadic rates seen from the Southern
Hemisphere are slowly increasing toward a July maximum. From south of the
equator one would expect to see approximately seven random meteors per hour
during the late morning hours and three per hour during the evening.
Anthelion (Sagittarids) 16:08 (242) -20
Hourly Rate = 1 N. Hemisphere, 2 S. Hemisphere
Eta Lyrids (IAA) 19:08 (287) +44
Hourly Rate = 1 N. Hemisphere, 0 S. Hemisphere
Beta Corona Australids (CAU) 18:16 (274) -41
Hourly Rate = 0 N. Hemisphere, <1 S. Hemisphere
Eta Aquarids (ETA) 22:40 (340) -01
Hourly Rate = 10 N. Hemisphere, 10 S. Hemisphere
Clear Skies!
Robert Lunsford
American Meteor Society |
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