(meteorobs) Meteor Activity Outlook for April 23-29, 2011

[lunro.imo.usa at cox.net]

During this period the moon reaches its last quarter phase on Monday April 25. At this time the moon will lie ninety degrees east of the sun and will rise near 0100 LDT (Local Daylight Time) for those situated in the mid-northern latitudes. While the moonlight will cause interference for meteor observing, the effects will be much less than when the moon is near its full phase. The estimated total hourly rates for evening observers this week is near two 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 nine from the northern hemisphere and twelve as seen from south of the equator. 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 reduced 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 April 23/24. 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:

The elusive Pi Puppids (PPU) are now active from a radiant located at 07:20 (110) -45. This area of the sky lies in south-central Puppis near the third magnitude star Sigma Puppis. This radiant is best placed as soon as it becomes dark as it culminates during the afternoon hours when the sun is still above the horizon. These meteors are nearly non-existent away from the night of April 24th. Even on that night it would be lucky to spot just one, especially from the northern hemisphere, where the radiant lies low in the southwest at dusk. This shower has produced outbursts in the past so it should be monitored whenever possible, especially from the southern hemisphere. With an entry velocity of only 18 km/sec., the average Pi Puppid meteor would crawl through the sky at a snails pace.

Studies of the IMO video database by Sirko Molau and Juergen Rendtel has revealed a weak radiant active at this time in the constellation of Virgo. Video data shows that the Sigma Leonids (SLE) are active from April 18th through the 25th with maximum activity falling on the 21st. The radiant is currently located at 13:46 (207) +04. This position lies in eastern Virgo, five degrees northwest of the fourth magnitude star Tau Virginis. The radiant is best placed near midnight LDT, when it lies highest above the horizon. At 20km/sec. the Sigma Leonids would produce obvious, slow meteors. Expected rates are less than one per hour no matter your location.

There is also a second new radiant active in Virgo this time of year. Video data 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 your location.

The wide Antihelion (ANT) radiant is now centered at 15:04 (226) -18. This area of the sky lies in central Libra, four degrees southeast of the third magnitude star Zubenelgenubi (Alpha Librae). This radiant is best placed near 0200 LDT when it lies on the meridian and is located highest in the sky. Due to the large size of this radiant, any meteor radiating from Libra, extreme eastern Hydra, northern Lupus, or western Scorpius could be a candidate for this shower. Rates at this time should be near one per hour as seen from the northern hemisphere and two per hour as seen from south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of medium-slow speed.

The major shower known as the Lyrids (LYR) are active from April 16th through the 25th. Maximum activity occurs on the 23rd. The radiant is currently located at 18:13 (273) +32. This position lies on Hercules/Lyra border, nine degrees southwest of the brilliant blue-white zero magnitude magnitude star known as Vega (Alpha Lyrae). The radiant is best placed during the last dark hour before dawn, when it lies highest above the horizon. At 48km/sec. the Lyrids would produce meteors of medium velocity. Expected rates this weekend are near two per hour during the last dark hour before dawn. Due to the northerly declination of the radiant, these meteors are not well seen from high southern latitudes.

The team of Sirko Molau and Juergen Rendtel have a third weak radiant active at this time in the constellation of Cygnus. Video data shows that the Nu Cygnids (NCY) are active from April 18th through May 7th. Maximum activity occurred on the morning of April 20th. The radiant is currently located at 20:50 (312) +42. This position lies in central Cygnus, three 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. At 42km/sec. the Nu Cygnids would produce meteors of medium velocity. Expected rates are near one per hour during the last dark hour before dawn. Due to the northerly declination of the radiant, these meteors are not well seen from south of the equator.

Activity from the Eta Aquariids (ETA) may be seen late next week. This major shower is active from April 28 through May 21. This shower is caused by particles from Halley's Comet, produced in Earth-crossing orbits many centuries ago. We pass closest to these orbits from May 5 through the 9th. During this period the Eta Aquariids are at their best, capable of producing ZHR's of seventy. The actual visible rates are most often less than half this figure due to the low altitude of the radiant at dawn. Observed hourly rates at maximum normally vary from zero at 60 degrees north latitude to 25 near the equator and back down to near zero again in Antarctica, where the radiant elevation is very low. Hourly rates this week are anywhere from zero to two per hour depending on your latitude and observing conditions. Rates will increase significantly as we approach the May 7 maximum. On April 28, the radiant will be located at 22:12 (333) -04. This area of the sky is located in northern Aquarius, three degrees southwest of the fourth magnitude star Gamma 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. No matter your location these meteors will appear from the eastern sky and shoot in all
directions. If the radiant has sufficient altitude Eta Aquariid meteors can also be seen shooting down toward the eastern horizon. With an entry velocity of 67 kilometers per second, a majority of these meteors will appear to move swiftly with a high percentage of the bright meteors leaving persistent trains. Surprisingly, this shower produces very few fireballs.

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 nine 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 reduced due to moonlight.

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

Pi Puppids (PPU) 07:20 (110) -45   Velocity - 18km/sec
Northern Hemisphere - <1 per hour Southern Hemisphere - <1 per hour

Sigma Leonids (SLE) 13:46 (207) +04   Velocity - 20km/sec
Northern Hemisphere - <1 per hour Southern Hemisphere - <1 per hour

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

Antihelion (ANT) 15:04 (226) -18   Velocity - 30km/sec
Northern Hemisphere - 1 per hour Southern Hemisphere - 2 per hour

Lyrids (LYR) 18:13 (273) +32   Velocity - 48km/sec
Northern Hemisphere - 2 per hour Southern Hemisphere - <1 per hour

Nu Cygnids (NCY) 20:50 (312) +42   Velocity - 42km/sec
Northern Hemisphere - <1 per hour Southern Hemisphere - <1 per hour

Eta Aquariids (ETA)   22:12 (333) -04   Velocity - 67km/sec
Northern Hemisphere - <1 per hour Southern Hemisphere - 1 per hour

Clear Skies!

Robert Lunsford
American Meteor Society