During this period the moon reaches its full phase on Thursday April 25th. At this time the moon is located opposite the sun and will lie above the horizon all night long. This weekend the waxing gibbous moon will set during the late morning hours and allow a very short period of dark skies for meteor observing. The estimated total hourly meteor rates for evening observers this week is near three as seen from the northern hemisphere and four as seen from south of the equator. For morning observers the estimated total hourly rates should be near seventeen no matter your location. 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. Evening rates are reduced during this period due to the bright moon.
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 20/21. 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) may be seen from the southern hemisphere from a radiant located at 07:16 (109) -45. This area of the sky is located central Puppis, just 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 are expected to be low. Observers located in the tropical northern hemisphere may also see some activity but at latitudes north of 30 degrees north, the odds are against seeing any activity at all. At 18km/sec. the Pi Puppids would produce meteors of very slow velocity.
The Sigma Leonids B (SLE) is the second of two branches of this shower. This shower was first noticed by Terentjeva (1990) in her analysis of 554 fireball orbits. This particular branch is active from April 18-26, with maximum activity occurring on the evening of the 19th. The radiant is currently located near 13:32 (203) +03. This position actually lies in central Virgo (not Leo), three degrees north of the third magnitude star Heze (Zeta Virginis). The radiant is best placed near 0100 when it lies highest above the horizon. This shower can be seen equally well from both hemispheres and may be partially responsible for the April fireballs. At 20km/sec. this shower would produce meteors of slow velocity.
The center of the large Anthelion (ANT) radiant is currently located at 14:44 (221) -16. This position lies in western Libra, just west of the third magnitude double star known as Zubenelgenubi (Alpha 2 Librae). 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 Anthelion meteor would be of slow velocity.
Activity from the Lyrid (LYR) shower reaches maximum activity on the morning of April 22th with the radiant located at 18:08 (272) +33. This area of the sky is actually located in eastern Hercules, two degrees southwest of the faint star known as Kappa Lyrae. This position also lies six degrees southwest of the brilliant zero magnitude 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. Hourly rates at maximum are expected to be 10-15 shower members during the short time between moon set and dawn, when the sky is totally dark. South of the equator rates would most likely be near 5 Lyrids per hour. 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 2 through May 4 with maximum activity occurring on April 18. The current radiant position lies at 20:40 (310) +43. This position lies in central Cygnus, two degrees south of the bright first magnitude star known as Deneb (Alpha Cygni). Rates are expected to be near one shower member per hour during the last couple of hours before dawn. While well placed for the northern hemisphere, this radiant is poorly seen from the southern hemisphere. 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 one 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 two per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Evening rates are reduced due to bright moonlight.
The table below presents a condensed version of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning .
|SHOWER||DATE OF MAXIMUM ACTIVITY||CELESTIAL POSITION||ENTRY VELOCITY||CULMINATION||HOURLY RATE||CLASS|
|RA (RA in Deg.) DEC||Km/Sec||Local Daylight Time||North-South|
|Pi Puppids (PPU)||Apr 23||07:16 (109) -45||18||19:00||<1 – <1||III|
|Sigma Leonids B (SLE)||Apr 20||13:32 (203) +03||20||01:00||2 – 2||II|
|Anthelions (ANT)||–||14:44 (221) -16||30||02:00||2 – 2||II|
|Lyrids (LYR)||Apr 22||18:08 (272) +33||48||05:00||10 – 5||I|
|Nu Cygnids (NCY)||Apr 18||20:40 (310) +43||42||07:00||<1 – <1||IV|