March 10, 2013 Leave a 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.
As seen from the northern hemisphere, March is the slowest month for meteor activity. No major annual showers are active and only a few very weak minor showers produce activity this month. The sporadic rates are also near their annual minimum so there is not much to look forward to this month except for the evening fireballs that seem to peak this time of year from the northern hemisphere. This could be due to the fact the Antapex radiant lies highest above the horizon this time of year during the evening hours. From the southern hemisphere, activity from the Centaurid complex begins to wane with only the weak activity visible from Norma and perhaps others areas nearby. At least southern sporadic rates are still strong to make the late summer viewing a bit more pleasurable.
During this period the moon reaches its new phase on Monday March 11th. At this time the moon is located near the sun and cannot be seen at night. Late in this period the waxing crescent moon will enter the evening sky but will not interfere with meteor observing whatsoever. The estimated total hourly meteor rates for evening observers this week is near two as seen from the northern hemisphere and five 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 eighteen 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.
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 March 9/10. 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:
On the last day of this period, members of the Northern March Virginids (NVI) should become visible as this shower peaks on the first day of its activity. The radiant is expected to be located at 11:34 (174) +09. This position is located near the Leo-Virgo border between the faint stars Iota Leonis and Nu Virginis. These meteors are best seen near 0100 local daylight time (LDT) when the radiant lies highest above the horizon. Rates would mostly likely be less than one shower member per hour, no matter your location. Since this radiant is located near the celestial equator, this activity can be seen most everywhere. At 22 km/sec. these meteors would have a slow velocity.
The large Anthelion (ANT) radiant is currently centered at 12:08 (182) -02. This position lies in western Virgo, two degrees southwest of the fourth magnitude star Zaniah (Eta Virginis). These meteors may be seen all night long but the radiant is best placed near 0200 LDT when it lies on the meridian and is highest in the sky. Rates at this time should be near two per hour no matter your location. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of slow velocity.
The Gamma Normids (GNO) are active from a radiant located at 15:40 (235) -50. This position lies in western Norma, five degrees northeast of the third magnitude star Zeta Lupi. Due to the southerly declination (celestial latitude) 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 peaks on March 13 so current hourly rates would be near two per hour as seen from south of the equator and less than one per hour as seen from northern latitudes. At 56km/sec. the Gamma Normids would produce mostly swift meteors.
On Monday March 11, activity from the Xi Herculids (XHE) should become detectable. The peak occurs on Wednesday March 13th when the radiant is located at 17:11 (258) +48. This position is located in northern Hercules, five degrees southwest of the third magnitude star Rastaban (Beta Draconis). 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 should be near one shower member per hour as seen from the northern hemisphere. These meteors are not well seen south of the equator as the radiant does not rise very high from points south of the equator. At 37 km/sec. these meteors would have a medium velocity.
As seen from the mid-northern hemisphere (45N) one would expect to see approximately five 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 four per hour during the evening hours. Locations between these two extremes would see activity between the listed figures.
The list below presents a condensed version of the expected activity this week.
Rates and positions are exact for Saturday night/Sunday morning .
Northern March Virginids (NVI) – 11:34 (174) +09 Velocity – 22km/sec.
Northern Hemisphere – <1 per hr. Southern Hemisphere – <1 per hr
Anthelions (ANT) – 12:08 (182) -02 Velocity – 30km/sec.
Northern Hemisphere – 2 per hr. Southern Hemisphere – 2 per hr
Gamma Normids (GNO) – 15:40 (235) -50 Velocity – 56km/sec.
Northern Hemisphere – <1 per hr. Southern Hemisphere – 2 per hr
Xi Herculids (XHE) – 15:43 (236) +42 Velocity – 37km/sec.
Northern Hemisphere – 1 per hr. Southern Hemisphere – <1 per hr
American Meteor Society