Meteor Activity Outlook for April 20-26, 2001

By Robert Lunsford

The moon is new on Monday April 23. This will be the best week of the month to view meteor activity and luckily the Lyrids peak this coming Sunday. The estimated total hourly rates for evening observers this week should be near 1 for those located in the Northern Hemisphere and 3 for those located in the Southern Hemisphere.

For morning observers the estimated total hourly rates would be near 10 for the Northern Hemisphere and 13 for those located in the Southern Hemisphere. 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 for meteor activity.

The positions listed below are exact for Saturday night/Sunday morning April 21/22. The positions do not change greatly day to day so these positions may be used during this entire period.

For southern observers the Pi Puppids are now active. This radiant is currently located at 07:16 (109) -45. This area of the sky is located in south-central Puppis 3 degrees southwest of the 2nd magnitude star Sigma Puppi. It is a full 10 degrees south of Pi Puppi so perhaps this shower should be called the Sigma Puppids?

Puppis is located low in the southwestern sky after sunset for those north of the equator and much higher in the western sky for those located further south. Regardless of your location activity is best seen as soon as it becomes dark. The best (if any) activity will occur after sunset Sunday evening. Even at maximum activity this radiant can be quiet. The Pi Puppids are most active when periodic comet Grigg-Skjellerup is near perihelion. This will next occur in 2002. These meteors are extremely slow.

The Antihelion radiant is now located at 15:04 (226) -16. This area of the sky is located in central Libra close to the faint star Nu Librae. Any slow to medium speed meteor from Libra, southeastern Virgo, or northwestern Scorpius may be a good candidate for this shower. This area of the sky is best placed near 0200 local daylight time (0100 local standard time) when it lies on the meridian.

At this time I expect to see perhaps 1 per hour from site in the Northern Hemisphere and 2 meteors per hour from the Southern Hemisphere. Unlike most of the annual showers the antihelion radiant is produced by debris from unknown sources orbiting in a direct motion like the earth. These sources are most likely asteroids, which produce stony and metallic debris whose density is much greater that produced by comets.

This debris collides with the earth on the inbound portion of its orbit, before its closest approach to the sun. Therefore we best see them just after midnight when we are facing the direction from which this activity appears. The antihelion radiant is active all year from an area of the sky nearly opposite that of the sun. The radiant will travel approximately one degree eastward per day and travels through many different constellations over the course of a year.

It is easiest to simply list these meteors as "ANT" but a majority of meteor organizations prefer that you list them from the constellation in which the radiant is currently located or the constellation where the shower reaches maximum activity. For instance those who share reports with the IMO should now label these meteors as Sagittarids (SAG).

Lyrid will reach maximum activity on Sunday the 22nd. The radiant position lies at 18:04 (271) +34. This position lies in extreme eastern Hercules and just 2 degrees southwest of the 4th magnitude star Kappa Lyrae. For observers in the Northern Hemisphere this area of the sky rises near 2100 (9pm) local daylight time (2000 local standard time).

For areas south of the equator it rises much later. It is best seen from all locations near 0400 local daylight time (0300 local standard time) when it lies high overhead for northern observers and low in the north for southern observers. Lyrid rates will be 1-2 per hour Thursday through Saturday and will then surge on Sunday to 10-15 per hour between 0200 and dawn local daylight time. Rates could be better than this but the average falls between 10 and 15 per hour.

Much less activity is seen from the Southern Hemisphere where the radiant lies low in the north at dawn. Rates will fall back down to 1-2 per hour Monday and then below 1 per hour by Wednesday. Lyrid meteors possess a medium entry velocity of 49 km/sec. This will produce meteors that are slow if seen close to the radiant or close to the horizon. Those seen far from the radiant and high in the sky will travel at medium speeds.

The Lyrids have been known to produce fireballs, brilliant meteors brighter than any of the stars. Lyrid meteors are produced by the debris from comet Thatcher (1861 I). There have been surprising Lyrid displays throughout history when rates have approached and exceeded 100 meteors per hour. Don't miss this favorable opportunity to view the Lyrids!

The Northern Apex radiant is now located at 20:04 (301) -05. This position lies in a remote area of southeastern Aquila. This area of the sky is best placed for viewing during the last dark hour before dawn. Since this radiant is diffuse any meteors from southeastern Aquila, northeastern Sagittarius, northwestern Capricornus, western Aquarius, or southern Delphinus could be a good candidate.

As seen from the Northern Hemisphere this source should produce at least 1 meteor per hour during the last few hours before dawn. Rates seen from the Southern Hemisphere should be better with perhaps 2 of these meteors being seen per hour. Like the antihelion radiant both apex radiants are active all year long and travel approximately one degree eastward per day. Unlike the antihelion debris these particles orbit the sun in a retrograde motion opposite that of the earth and are most likely produced by unknown comets. They strike the earth after their closest approach to the sun. Since they are moving in opposite directions these particles strike the earth at tremendous velocities often creating bright meteors with persistent trains.

These particles strike the earth on the morning side of earth and are best seen just before morning twilight while the sky is still perfectly dark. There are meteors with a zero inclination that radiate precisely from the apex point on the ecliptic, exactly 90 degrees west of the sun. These meteors are rare though as the earth orbits the sun it "sweeps clean" much of the material that shares the same orbit. Much more debris is located just north and south of the earth's orbit with slightly higher or lower inclinations. This creates the northern and southern branches of the apex activity.

Meteors from both branches are normally included in the sporadic count but should also be noted in some manner as to which branch of the apex complex they appear to radiate.

The Southern Apex source lies exactly 30 degrees south of its northern counterpart at 20:04 (301) -35. This position lies in southeastern Sagittarius just 1 degree east of the 4th magnitude star Theta 1 Sagittarii. Like the northern apex these meteors are best seen toward dawn when the radiant lies highest above the horizon in a dark sky. Any meteor from southeastern Sagittarius, Microscopium, or southwestern Capricornus could possibly be a candidate from this source.

As seen from the Northern Hemisphere this source now lies so low in the southeastern sky that chances are little or no activity will be seen. With the radiant being situated much higher in the sky, rates seen from the Southern Hemisphere should be better with perhaps 2-3 of these meteors being seen per hour.

The Eta Aquarids are now beginning their long run of activity. They will be active for the next 5 weeks with a maximum on May 5. See them now and after maximum as May 5 coincides with the full moon. Current rates are most likely 1 per hour during the last hour before morning twilight.

The current radiant position lies at 21:36 (324) -07. This area of the sky is located in western Aquarius 2 degrees east of the 3rd magnitude star Beta Aquarii. This shower is difficult to see north of 45 degrees north latitude as the radiant does not rise very high before the beginning of morning twilight. The north and south tropical areas as well as Australia and Southern Africa enjoy the best view of this shower.

These meteors have a geocentric velocity of 66 km/sec., which means they would appear to move slowly if seen near the radiant or near the horizon. If seen far from the radiant and high in the sky then they would appear to move swiftly. The Eta Aquarids also produce a high percentage of persistent trains.

The Sporadic rates for the Northern Hemisphere are now in decline and will do so until June. One would expect to see perhaps 5 random meteors per hour during the last hours before dawn from rural observing sites. During the evening hours perhaps 1 random meteor can be seen per hour. Rates seen from the Southern Hemisphere would now be slightly better than those seen in the Northern Hemisphere with perhaps 6 random meteors being seen per hour during the late morning hours and 2 per hour during the evening.