Meteor Activity Outlook for April 18-24, 2009

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 27th, with a pronounced maximum on the 22nd and 23rd. The Eta Aquariids start appearing near the 27th 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 wanes from its last quarter phase down to almost new at the end of this period. The crescent moon will not interfere with observing as long as you are able to keep it out of your field of view while observing. The estimated total hourly rates for evening observers this week is near two as seen from the northern hemisphere and three for those situated south of the equator. For morning observers the estimated total hourly rates should be near ten for those located in the mid-northern hemisphere (45 N) and fifteen for those viewing from the mid-southern hemisphere (45 S). Locations between these two extremes would see activity between the listed figures. These rates assume that you are watching from rural areas away from all sources of light pollution. 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 positions and rates listed below are exact for Saturday night/Sunday morning April 18/19. 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 Pi Puppids (PPU) is a relatively new shower with most of the activity occurring when the parent comet (26P Grigg-Skjellerup) is near perihelion. This comet was last at perihelion in March 2008 so a trace of activity from this shower is not out of the question. The radiant for this shower lies far to the south and is nearly impossible to detect north of thirty degrees north latitude. The radiant position lies at 07:18 (110) -45. This area of the sky is located in southern Puppis, two degrees southwest of the third magnitude star Sigma Puppis. The radiant lies highest in a dark sky as soon as it becomes dark at the end of evening twilight. Peak activity occurs on April 23. Away from this night rates are expected to be far less than one per hour. With an entry velocity of only 18 kilometers per second, these meteors will appear to move very slowly. Shower members are usually quite bright which may also aid in their identification.

The wide Antihelion (ANT) radiant is now centered at 14:44 (221) -16. This area of the sky lies in western Libra, only two degrees west of the second magnitude double star Zubenelgenubi (Alpha Librae). This radiant is best placed near 0200 LDT when it is located on the meridian and lies highest in the sky above the horizon. Due to the large size of this radiant, any meteor radiating from southeastern Virgo, Libra, or extreme eastern Hydra could be a candidate for this shower. Rates at this time should be near two per hour as seen from the southern hemisphere and only one as seen from north of the equator. With an entry velocity of 30km/sec., the average Antihelion meteor would be of medium-slow speed.

The Lyrids (LYR) are the first major annual shower of the season. ZHR's reach one on April 16th and remain at or slightly above this level through April 27. According to the IMO calendar, peak rates will occur on Wednesday April 22 near 11:00 Universal Time. This timing favors the western half of North America where observers will have the radiant located high in a dark sky, as long as you are not situated too far north where morning twilight begins to interfere at this time. Sirko Molau's video data lists the peak on the 23rd, so observers are encouraged to observe on both nights if possible. ZHR's average eighteen but raw visual rates can vary from 5-25, depending on your observing conditions. The radiant currently lies at 17:52 (268) +34. This area of the sky is located in eastern Hercules, twelve degrees southwest of the brilliant zero magnitude star Vega (Alpha Lyrae). The radiant rises in the northeastern sky during the late evening hours for most locations in the Northern Hemisphere. One should wait until the radiant reaches an elevation of thirty degrees before commencing observations. At lower radiant elevations only a small fraction of the Lyrid activity can be seen. For 30 degrees north latitude this occurs near midnight. The radiant would reach thirty degrees elevation earlier for locations further north and later for locations further south. The best time to view this activity is just before the start of morning twilight, when the radiant lies highest in a dark sky. With an entry velocity of 46 kilometers per second, a majority of these meteors will appear to move with moderate to swift speeds. The Lyrids are also known to produce a fair amount of meteors with persistent trains and an occasional fireball.

The video studies of Sirko Molau have revealed a weak radiant active in Cygnus this time of year. The Xi Cygnid (XCG) radiant is currently located at 20:20 (305) +40. This area of the sky is located in central Cygnus, only two degrees west of the second magnitude star Sadr (Gamma Cygni). Maximum activity occurs on April 27 so current rates are expected to remain less than one per hour. These meteors are best seen during the last dark hour before dawn, when the radiant lies highest above the horizon in a dark sky. This shower is best seen from the northern hemisphere, where the radiant lies high in the sky at dawn. At 44 km/sec. the Xi Cygnids will usually produce meteors of medium velocity.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately seven 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 thirteen 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 table below presents a summary of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning but may be used all week.