During this period the moon reaches its first quarter phase on Thursday April 14th. On that date the moon will be located 90 degrees east of the sun and will set during the mid-morning hours. This weekend the waxing crescent moon will set during the late evening hours and will not pose any problems for viewing meteor activity as long as you keep the lunar glare out of your field of view. The estimated total hourly meteor rates for evening observers this week is near 3 for observers located in the northern hemisphere and 4 for observers located south of the equator. For morning observers the estimated total hourly rates should be near 8 as seen from mid-northern latitudes (45N) and 11 as seen from tropical southern locations (25S). 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. Note that the hourly rates listed below are estimates as viewed from dark sky sites away from urban light sources. Observers viewing from urban areas will see less activity as only the brightest meteors will be visible from such locations.
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 9/10. 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 far 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.
These sources of meteoric activity are expected to be active this week.
The sigma Leonids (SLE) were first documented by Cuno Hoffmeister back in the 1940’s. Recent analysis show these meteors are active from April 8-25 with maximum activity occurring on the 15th. The radiant is currently located at 13:12 (198) +03. This area of the sky is actually located in central Virgo, 3 degrees east of the 3rd magnitude star known as Auva (delta Virginis). I’m not certain why this source is called the Sigma Leonids as even Hoffmeister placed the radiant in central Virgo, far from the star known as sigma Leonis. Perhaps back then there was a source of activity thought to be in southeastern Leo active at the same time? This radiant is best placed near 0001 local summer time when it lies highest above the horizon. Rates are currently less than 1 per hour and may approach 1 per hour at maximum. With an entry velocity of 19 km/sec., the average meteor from this source would be of slow velocity.
The center of the large Anthelion (ANT) radiant is currently located at 14:12 (213) -13. This position lies in southeastern Virgo, 3 degrees south of the faint star known as kappa Virginis. Due to the large size of this radiant, Anthelion activity may also appear from the nearby constellations of Libra, eastern Hydra, and Serpens Caput as well as Virgo. This radiant is best placed near 0200 local summer time, when it lies on the meridian and is located highest in the sky. Rates at this time should be near 3 per hour no matter your location. With an entry velocity of 30 km/sec., the average Anthelion meteor would be of slow velocity.
The April rho Cygnids (AEC) were discovered by Dr. Peter Brown during his meteoroid stream survey using the Canadian Meteor Orbit Radar. These meteors are active from April 11-May 4 with maximum activity occurring on the 22nd. The radiant is currently located at 20:18 (304) +41. This area of the sky is located in central Cygnus, just 1 degree northwest of the 2nd magnitude star known as Sadr (gamma Cygni). This radiant is best placed during the last hour before dawn when it lies highest above the horizon in a dark sky. Current rates are expected to be less than 1 per hour. With an entry velocity of 42 km/sec., the average meteor from this source would be of medium velocity. Note that these meteors are synonymous with the Nu Cygnids (Molau and Rendtel, 2009).
The delta Aquiliids (DAL) were discovered by Dr. Peter Jenniskens and mentioned in his book “Meteor Showers and their Parent Comets”. Recent analysis show these meteors are active from April 7-13 with maximum activity occurring on the 9th. At maximum the radiant is located at 20:32 (308) +12. This area of the sky is actually located in central Delphinus just north of the 4th magnitude star known as Deneb Dulfim (epsilon Delphini). This radiant is best placed during the last hour before dawn when it lies highest above the horizon in a dark sky. Rates at maximum are expected to remain less than 1 per hour. With an entry velocity of 63 km/sec., the average meteor from this source would be of fast velocity.
As seen from the mid-northern hemisphere (45N) one would expect to see approximately 5 sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near 2 per hour. As seen from the tropical southern latitudes (25S), morning rates would be near 8 per hour as seen from rural observing sites and 3 per hour during the evening hours. Locations between these two extremes would see activity between the listed figures.
The list below offers the information from above in tabular form. Rates and positions are exact for Saturday night/Sunday morning except where noted in the shower descriptions.
|SHOWER||DATE OF MAXIMUM ACTIVITY||CELESTIAL POSITION||ENTRY VELOCITY||CULMINATION||HOURLY RATE||CLASS|
|RA (RA in Deg.) DEC||Km/Sec||Local Summer Time||North-South|
|sigma Leonids (SLE)||Apr 05||13:12 (198) +03||19||01:00||<1 – <1||IV|
|Anthelions (ANT)||–||14:12 (213) -13||30||02:00||3 – 3||II|
|April rho Cygnids (AEC)||Apr 22||20:18 (304) +41||42||08:00||<1 – <1||IV|
|delta Aquiliids (DAL)||Apr 09||20:32 (308) +12||63||08:00||<1 – <1||IV|