February 17, 2013 1 Comment
The following is a slightly edited version of Bob Lunsford’s excellent weekly summary of meteor activity. The original version can be found at the American Meteor Society’s site.
February offers the meteor observer in the northern hemisphere a couple of weak showers plus falling sporadic rates. This may not seem too exiting but you never know when surprises are in store. An errant earth-grazer from the Centaurid complex may shoot northward. Better yet, a bright fireball may light up the sky. February is the start of the fireball season, when an abundance of fireballs seem to occur. This lasts well into April and seems to occur mostly during the early evening hours.
Observers in the southern hemisphere are treated to the Alpha Centaurid peak on the 8th plus the entire Centaurid complex of radiants is active all month long. Sporadic rates also peak this month south of the equator this month adding to the celestial show.
During this period the moon reaches its first quarter phase on Sunday February 17th. At this time the moon is located ninety degrees east of the sun and sets near midnight local standard time (LST) as seen from mid-northern latitudes. As the week progresses the waxing gibbous moon will set during the early morning hours, allowing a few hours of dark skies between the time of moon set and the beginning of morning twilight. The estimated total hourly meteor rates for evening observers this week is near two as seen from the northern hemisphere and four as seen from south of the equator. For morning observers the estimated total hourly rates should be near eight from the mid-northern hemisphere and seventeen from the mid-southern hemisphere. 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. Evening rates are reduced during this period due to moonlight.
The radiant (the area of the sky where meteors appear to shoot from) positions and rates listed below are exact for Saturday night/Sunday morning February 16/17. These positions do not change greatly day to day so the listed coordinates may be used during this entire period.
The following showers are expected to be active this week:
The large Anthelion (ANT) radiant is currently centered at 10:44 (161) +07. This position lies in southern Leo, ten degrees southeast of the first magnitude star Regulus (Alpha Leonis). These meteors may be seen all night long but the radiant is best placed near 0100 LST when it lies on the meridian and is highest in the sky. Rates at this time should be near one per hour no matter your location. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of slow velocity.
The Alpha Centaurids (ACE) are active from a radiant located at 14:43 (221) -62. This position lies in southeastern Centaurus, very close to the position occupied by the zero magnitude star Rigel Kentaurus (Alpha Centauri). These meteors cannot be seen north of the northern tropical regions. They are best seen from mid-southern latitudes where the radiant lies high in the sky near 0500 local summer time. This shower peaked on February 8th so current rates would be near one per hour as seen from the southern hemisphere. At 56km/sec. the Alpha Centaurids would produce mostly swift meteors.
The Beta Herculids are active through Tuesday from a radiant located at 15:52 (238) +28. This position is actually located in Corona Borealis, four degrees northeast of the second magnitude star Alphecca (Alpha Coronae Borealis). It is suggested that the observer be liberal with shower association as the actual radiant position is not well defined. These meteors are best seen near during the last dark hour before dawn when the radiant lies highest above the horizon in a dark sky. Rates would mostly likely be less than one shower member per hour, no matter your location. Observers in the northern hemisphere have an advantage in that the radiant lies higher in the sky during the morning hours. At 56 km/sec. the Beta Herculids would produce mostly swift meteors.
The IMO video list of radiants has several entries for the Delta Serpentids (DSE). On most nights of possible activity this shower is extremely weak, far less than the weak sporadic rate seen this time of year from the northern hemisphere. On the morning of the February 16th though, it becomes the second most active radiant in the sky. At that time the radiant is located at 16:37 (249) +09, which actually places it in among the stars of Ophiuchus. The nearest bright stars are fourth magnitude Kappa and Iota Ophiuchi, which lie six degrees to the east. This position is well seen from either side of the equator. These meteors are best seen near during the last dark hour before dawn when the radiant lies highest above the horizon in a dark sky. On other mornings rates for this shower are so weak that the chance of sporadic alignment is extremely high. At 57 km/sec. the Delta Serpentids would produce mostly swift meteors.
As seen from the mid-northern hemisphere (45N) one would expect to see approximately six sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near one per hour. As seen from the mid-southern hemisphere (45S), morning rates would be near fourteen per hour as seen from rural observing sites and three per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Rates are reduced during the evening hours due to moonlight.
The list below presents a condensed version of the expected activity this week.
Rates and positions are exact for Saturday night/Sunday morning .
Anthelions (ANT) – 10:44 (161) +07 Velocity – 30km/sec.
Northern Hemisphere – 1 per hr. Southern Hemisphere – 1 per hr
Alpha Centaurids (ACE) – 14:43 (221) -62 Velocity – 56km/sec.
Northern Hemisphere – <1 per hr. Southern Hemisphere – 1 per hr
Beta Herculids (BHE) – 15:52 (238) +28 Velocity – 56km/sec.
Northern Hemisphere – <1 per hr. Southern Hemisphere – <1 per hr
Delta Serpentids (DSE) – 16:37 (249) +09 Velocity – 57km/sec.
Northern Hemisphere – 1 per hr. Southern Hemisphere – 1 per hr
American Meteor Society