November 21, 2011 6 Comments
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, meteor rates continue to be strong in November. While no major activity is expected this month, the two Taurid radiants plus the Leonids keep the skies active. The addition of strong sporadic rates make November one of the better months to view meteor activity from north of the equator. Skies are fairly quiet as seen from the southern hemisphere this month. Activity from the three showers mentioned above may be seen from south of the equator, but the sporadic rates are much lower than those seen in the northern hemisphereDuring this period the moon reaches its new phase on Thursday November 25th. At that time the moon will lie near the sun and will not be visible at night. This weekend the waning crescent moon will be a nuisance in the late morning sky but will not inhibit meteor watching. If the moon is above the horizon simple face in a direction in which it lies outside of your field of view. The moon will be less of a problem with each passing night as it approaches the sun. The estimated total hourly rates for evening observers this week is near four as seen from the northern hemisphere and three as seen from the southern hemisphere. For morning observers the estimated total hourly rates should be near fifteen as seen from mid-northern latitudes and twelve from mid-southern latitudes. 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. Morning rates are slightly reduced this week 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 November 19/20. These positions do not change greatly day to day so the listed coordinates may be used during this entire period.
Remnants from the famous Andromedid (AND) shower, noted for intense storms during the 19th century, may still be seen throughout November. The current position of this large radiant is 01:38 (024) +39. This position lies in central Andromeda, two degrees south of the fourth magnitude star Upsilon Andromedae. The radiant is so diffuse that Andromedid meteors may also be seen coming from Triangulum, extreme northwestern Perseus, and southeastern Cassiopeia as well as Andromeda. Visual activity is expected to be low, but detectable. An inconspicuous maximum occured on November 12. The Andromedid meteors are best seen near 2200 (10pm) LST (Local Standard Time), when the radiant lies on the meridian. At 19km/sec., the average Andromedid will appear as a very slow moving meteor.
The last of the Omicron Eridanids (OER) will be seen this weekend from a radiant located at 04:06 (061) -03. This position lies in northeastern Eridanus, fifteen degrees northwest of the bright zero magnitude star Rigel (Beta Orionis). The radiant is best placed near 0100 LST, when it lies highest above the horizon. Meteors from the Omicron Eridanids strike the atmosphere at 27km/sec., which would produce meteors of slow velocity. Expected rates from this weak shower would be less than one per hour, no matter your location.
The Northern Taurids (NTA) are active from a large radiant centered at 04:22 (066) +24. This position lies in central Taurus, seven degrees north of the bright first magnitude orange star Aldebaran (Alpha Tauri). The radiant is best placed near 0100 LST, when it lies highest above the horizon. Since the radiant is large, Northern Taurid meteors may also appear to come from southwestern Auriga, southeastern Perseus, northwestern Orion, as well as Taurus. Meteors from the Northern Taurids strike the atmosphere at 29km/sec., which would produce meteors of slow velocity. Expected rates would be near two per hour, no matter your location.
The November Orionids (NOO) were recently discovered by Sirko Molau and Jueregen Rendtel by analyzing video data from the IMO network. For years this radiant was lost in the maze of radiants active this time of year. Due to the low activity, visual observers were unable to detect this shower. This shower is active from November 18 through December 9. Maximum activity occurs on November 30. Once you know the radiant in advance, this shower is actually quite noticeable, producing an average of two shower members per hour near maximum. The radiant is currently located at 05:35 (084) +16. This position lies in northern Orion, nine degrees northwest of the orange first magnitude star Betelgeuse (Alpha Orionis). These meteors are best seen near 0200 LST when the radiant lies on the meridian and highest above the horizon. At 44 km/sec. the November Orionids produce mostly medium velocity meteors.
The Leonids (LEO) should peak on November 18th. Up to five Leonids an hour may be seen during the morning hours this weekend. Rates will fall as the week progresses. The radiant is currently located at 10:22 (155) +21. This position lies in western Leo only two degrees north of the third magnitude star Algeiba (Gamma Leonis). At 71km/sec., the average Leonid is swift with a high percentage of trains. These meteors are best seen during the last hour before the onset of morning twilight, when the radiant lies highest above the horizon in a dark sky.
As seen from the mid-northern hemisphere (45N) one would expect to see approximately nine sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near three per hour. As seen from the mid-southern hemisphere (45S), morning rates would be near five per hour as seen from rural observing sites and two per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Morning rates are slightly reduced 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.
Shower Name RA DEC Vel Rates km/s NH SH AND Andromedids 01h 38m +39 19 <1 <1 OER Omicron Eridanids 04h 06m -03 27 <1 <1 NTA Northern Taurids 04h 22m +24 29 2 2 NOO November Orionids 05h 35m +16 44 1 1 LEO Leonids 10h 22m +21 71 3 2 RA - Right Ascension DEC - Declination Vel - Velocity relative to Earth (in km per sec) Rates - Rate of visible meteors per hour from a dark site NH - Northern Hemisphere SH - Southern Hemisphere