(meteorobs) Meteor Activity Outlook for April 21-27, 2012

Robert Lunsford lunro.imo.usa at cox.net
Thu Apr 19 18:43:24 EDT 2012

During this period the moon reaches its new phase on Saturday the 21st. At this time the moon will be near the sun and will not be visible at night. This will be the best time of the month in which to view meteor activity.  As the week progresses the waxing crescent moon will enter the evening sky but will not be bright enough to interfere with observing. In addition the moon will set during the evening hours allowing the more active morning to be free from any interfering moonlight.  The estimated total hourly rates for evening observers this week is near three for observers in the northern hemisphere and four for those south of the equator. For morning observers the estimated total hourly rates should be near twenty-three as seen from mid-northern latitudes and nineteen 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.

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 April 21/22. 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. It must be remembered that meteor activity is rarely seen at the radiant position. Rather they shoot outwards from the radiant so it is best to center your field of view so that the radiant lies at the edge and not the center. Viewing there will allow you to easily trace the path of each meteor back to the radiant (if it is a shower member) or in another direction if it is a sporadic. 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.

The following showers are expected to be active this week:

Activity from the Pi Puppids (PPU) continues this week from a radiant located at 07:16 (109) -45. This area of the sky is located central Puppis, two degrees southwest of the third magnitude star Sigma Puppis. This area of the sky is best seen as soon as it becomes dark during the early evening hours. Maximum activity is predicted to occur on Sunday evening the 22nd (23rd UT). Despite this, rates less than one per hour are expected, no matter your location. Observers located in the southern hemisphere have a much better view of this activity as the radiant lies higher in the sky. At 18km/sec. the Pi Puppids would produce meteors of very slow velocity.

The weak shower known as the Sigma Leonids (SLE) is active from a radiant located at 13:40 (205) +04, which actually lies in northern Virgo, four degrees northeast of the third magnitude star Zeta Virginis. One might feel this shower was named for the wrong constellation, but the case is more likely that visual observations, made before the advent of video methods, placed the radiant incorrectly further westward in Leo. This radiant is best placed near 0300 local daylight time (LDT), when it lies on the meridian and is located highest in the sky. Rates at this time would be less than one per hour no matter your location. With an entry velocity of 20 km/sec., the average Sigma Leonid meteor would be of very slow velocity.

There is also another radiant active in Virgo this time of year. Video data from The IMO shows that the h Virginids (HVR) are active from April 22-25 with maximum activity occurring on the 22nd. On the evening of the 21st (22nd UT), the radiant is located at 14:16 (214) -11. This position lies on the Virgo/Libra border, two degrees southeast of the fourth magnitude star Kappa Virginis. The radiant is best placed near 0200 LDT, when it lies on the meridian and is highest above the horizon. At 24km/sec. the h Virginids would produce more slow meteors. Expected rates would also be less than one per hour no matter the date or your location.

The large Antihelion (ANT) radiant is currently located at 14:56 (224) -16. This position lies in western Libra, only one degree southeast of the third magnitude star Zubenelgenubi (Alpha Librae). Due to the large size of this radiant, Antihelion activity may also appear from extreme eastern Hydra, eastern Virgo, northwestern Scorpius, as well as Libra. This radiant is best placed near 0200 LDT, when it lies on the meridian and is located highest in the sky. Rates at this time should be near two per hour as seen from the northern hemisphere and three as seen from south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of slow velocity.

The Lyrid (LYR) shower is expected to reach maximum activity on the night of April 21/22 with rates up to 15 shower members per hour. The radiant is located at 18:08 (272) +33. This area of the sky is actually located in extreme eastern Hercules, eight degrees southwest of the brilliant blue-white star Vega (Alpha Lyrae). The radiant is best placed just before the break of dawn when the radiant lies highest in the sky. While Lyrid meteors can be seen in both hemispheres, the north is favored as the radiant lies much higher in the sky. Rates will fall rapidly after maximum and little activity will be seen the remainder of the week. At 48km/sec. the Lyrids would produce meteors of medium-swift velocity. It should be noted that the Lyrids can occasionally produce bright meteors of fireball class magnitude.

Studies of the IMO video database by Sirko Molau and Juergen Rendtel has revealed a weak radiant active in the constellation of Cygnus this time of year. The Nu Cygnids (NCY) are active from April 18 through May 7 with maximum activity occurring on April 19. The current radiant position lies at 20:44 (311) +42. This position lies in central Cygnus, two degrees south of the first magnitude star Deneb (Alpha Cygni). The radiant is best placed during the last dark hour before dawn, when it lies highest above the horizon in a dark sky. Due to the northern declination of the radiant, this activity is not well seen from the southern hemisphere. No matter your location, rates are expected to be less than one per hour. At 42km/sec. the Nu Cygnids would produce meteors of average 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 two per hour. As seen from the mid-southern hemisphere (45S), morning rates would be near ten 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.

The list below presents a condensed version of the expected activity this week.
Rates and positions are exact for Saturday night/Sunday morning.

Pi Puppids (PPU) - 07:16 (109) -45   Velocity 18km/sec
Northern Hemisphere - <1 per hr Southern Hemisphere - <1 per hour

Sigma Leonids (SLE) - 13:40 (205) +04   Velocity 20km/sec
Northern Hemisphere - <1 per hr   Southern Hemisphere - <1 per hour

h Virginids (HVR) - 14:16 (214) -11   Velocity 24km/sec
Northern Hemisphere - <1 per hr   Southern Hemisphere - <1 per hour

Antihelion (ANT) - 14:56 (224) -16   Velocity 30km/sec
Northern Hemisphere - 2 per hr   Southern Hemisphere - 3 per hour

Lyrids (LYR) - 18:08 (272) +33   Velocity 48km/sec
Northern Hemisphere - 15 per hr   Southern Hemisphere - 5 per hour

Nu Cygnids (NCY) - 20:44 (311) +42   Velocity 42km/sec
Northern Hemisphere - <1 per hr   Southern Hemisphere - <1 per hour

Clear Skies!
Robert Lunsford
American Meteor Society

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