Meteor Activity Outlook for April 13-19, 2007

April has one major annual shower and the start of another. The Lyrids are active from April 16-25 and reach maximum activity on the 22nd. While not the strongest annual shower they produce much better rates than has been seen for the past three months. The Eta Aquarids also reach a ZHR of one on April 19 and slowly continue to increase in strength as the month progresses. Sporadic rates seen in the northern hemisphere are actually worse than those seen in March. This trend will continue through June. On the other hand rates seen from the southern hemisphere are increasing toward a July maximum.

During this period the moon reaches its new phase on Tuesday April 17. At this time the moon will rise and set with the sun and will not interfere with observing during this period. The estimated total hourly rates for evening observers this week is near two for those north of the equator and three for observers south of the equator. For morning observers the estimated total hourly rates should be near nine for northern observers and fifteen for those south of the equator. 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 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. Doing this 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 Antihelion (ANT) radiant is now centered at 14:32 (218) -15. This area of the sky is centered in western Libra, five degrees northwest of the third magnitude star Zubenelgenubi (Alpha Librae). This 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 one per hour as seen in the northern hemisphere and two per hour for those located south of the equator. With an entry velocity of 30 km/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 25. According to the IMO, peak rates will occur on Sunday April 22 near 22:30 Universal Time. This timing favors Asia where local observers will actually see the best rates on the morning of April 23. For North America this time corresponds to 6:30 PM EDT and 3:30 PM PDT on April 22, which of course is during daylight. Peak Lyrid rates seen from North America should be similar on both the mornings of the 22nd and 23rd. ZHR's average eighteen but raw visual rates can vary from 5-25, depending on your observing conditions. The radiant currently lies at 17:32 (263) +34. This area of the sky is located in central Hercules, four degrees southeast of the third magnitude star Pi Herculis. 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 49 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.

Sporadic rates are slowing decreasing for observers in the northern hemisphere and slightly rising for those south of the equator. One would expect to see perhaps seven random meteors during the last hour before dawn from rural observing sites located in the northern hemisphere. During the first dark hour after the end of evening twilight, perhaps two random meteors can be seen per hour. Sporadic rates increase as the night progresses so rates seen near midnight would be near four per hour. Late morning sporadic rates seen from the southern hemisphere are now near thirteen per hour from rural observing sites. During the first dark hour after the end of evening twilight, perhaps three random meteors can be seen per hour, increasing to eight by midnight.