(meteorobs) Meteor Activity Outlook for April 14-20, 2012

[Robert Lunsford]

During this period the moon wanes from its last quarter phase to nearly new. This weekend the waning crescent moon will rise during the early morning hours, disturbing the nearby sky but allowing dark views in the opposite direction. The moon wanes and rises later which each passing night, providing more favorable circumstances as time goes on. 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 seven as seen from mid-northern latitudes and eleven 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 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 April 14/15. 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) begins this weekend from a radiant located at 07:04 (106) -44. This area of the sky is located central Puppis, five 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.  No matter your location, rates will be low, far less than one per hour this early in the activity curve. 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) becomes active on the 18th and peaks on the 20th. The radiant is located at 13:32 (203) +05, which actually lies in northern Virgo near the faint star Sigma Virginis. One might feel this shower was named for the wrong "Sigma" star, 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.

The large Antihelion (ANT) radiant is currently located at 14:32 (218) -15. This position lies in eastern Libra, five degrees west 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, 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 no matter your location. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of slow velocity.

Activity from the Lyrid (LYR) shower is first detectable on April 16th and the shower reaches maximum activity 6 nights later. The radiant is currently located at 17:52 (268) +36. This area of the sky is actually located in eastern Hercules, close to the faint star known as Theta Herculis. 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 this early in the activity curve would be low, less than one per hour no matter your location. At 48km/sec. the Lyrids would produce meteors of medium-swift velocity.

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 20:20 (305) +39. This position lies in central Cygnus, two degrees southwest of the second magnitude star Sadr (Gamma 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 at this time 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 four 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 eight 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. Morning rates are slightly reduced during this period 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.

Pi Puppids (PPU) - 07:04 (106) -44   Velocity 18km/sec
Northern Hemisphere - <1 per hr Southern Hemisphere - <1 per hour

Sigma Leonids (SLE) - 13:32 (203) +05   Velocity 20km/sec
Northern Hemisphere - <1 per hr Southern Hemisphere - <1 per hour

Antihelion (ANT) - 14:32 (218) -15   Velocity 30km/sec
Northern Hemisphere - 2 per hr Southern Hemisphere - 2 per hour

Lyrids (LYR) - 17:52 (268) +36   Velocity 48km/sec
Northern Hemisphere - <1 per hr Southern Hemisphere - <1 per hour

Nu Cygnids (NCY) - 20:20 (305) +39   Velocity 42km/sec
Northern Hemisphere - <1 per hr Southern Hemisphere - <1 per hour

Clear Skies!
Robert Lunsford
American Meteor Society