(meteorobs) Meteor Activity Outlook for April 2-8, 2011

[lunro.imo.usa at cox.net]

Meteor activity picks up a bit during April as two major showers are active during the month. The first of these, the Lyrids, are active from the 16th through the 25th, with a pronounced maximum on the 22nd. The Eta Aquariids start appearing near the 28th and reach maximum activity during the first week in May. Sporadic rates are low but steady as seen from the mid-northern hemisphere (45 N). Sporadic rates seen from the mid-southern hemisphere (45 S) rise this month toward a maximum in July.

During this period the moon reaches its new phase on Sunday April 3. At this time the moon will be near the sun and is not visible at night. As the week progresses, the waxing crescent moon will enter the evening sky but will set long before the more active morning hours arrive. The estimated total hourly rates for evening observers this week is near three as seen from the northern hemisphere and four as seen from the southern hemisphere. For morning observers the estimated total hourly rates should be near ten from the northern hemisphere and fourteen 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.

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 2/3. 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 wide Antihelion (ANT) radiant is now centered at 13:48 (207) -10. This area of the sky lies in eastern Virgo, four degrees east of the bright first magnitude star Spica (Alpha Virginis). This radiant is best placed near 0200 local daylight saving time (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 southern Bootes, northern Centaurus, Corvus, or Virgo could be a candidate for this shower. 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 medium-slow speed.

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 Zeta Cygnids (ZCY) are active from March 27 through April 13 with maximum activity occurring on April 6. The current radiant position lies at 19:52 (298) +39. This position lies in central Cygnus, six degrees west 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 44km/sec. the Zeta Cygnids would produce meteors of average velocity.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately eight 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 twelve 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.

Antihelion (ANT) 13:48 (207) -10   Velocity - 30km/sec
Northern Hemisphere - 2 per hour Southern Hemisphere - 2 per hour

Zeta Cygnids (ZCY) 19:52 (298) +39   Velocity - 44km/sec
Northern Hemisphere - <1 per hour Southern Hemisphere - <1 per hour

Clear Skies!

Robert Lunsford
American Meteor Society