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(meteorobs) Meteor Activity Outlook for January 10-16, 2003



Title:

Meteor Activity Outlook for 
 January 10-16, 2003

By Robert Lunsford 
AMS Operations Manager

The moon reaches its first quarter phase on Friday January 10. At this time the moon will set near midnight, leaving the morning hours free of any lunar interference. Toward the end of this period the moon will be in the sky most of the night causing a major problem with observing. The estimated total hourly rates for evening observers this week should be near 3 for everyone regardless of location. For morning observers the estimated total hourly rates should be near 15 for those located in the Northern Hemisphere and 17 for those 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 meteor activity. Moonlight reduces evening rates during this period.

The positions listed below are exact for Saturday night/Sunday morning January 11/12. The positions do not change greatly day to day so these positions may be used during this entire period. Most star atlases (available at science stores and libraries) 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 location. Meteor activity is not seen from radiants that are located below the horizon. The radiants below are listed in a west to east manner in order of right ascension (celestial longitude). The radiants listed first are located further west therefore are accessible earlier in the night while those listed last rise later in the night. This list also provides the order of ascending velocity for each radiant with those listed first usually being much slower than those last on the list. Velocity should not be the prime factor for shower association as all showers can produce slow meteors. Slow meteors can be produced from normally swift showers, such as the Leonids, when meteors appear near the radiant or close to the horizon. The true velocity is only revealed in shower members seen far from the radiant and high in the sky.

The Antihelion source is now centered at 8:24 (126) +19. This area of the sky is located in central Cancer  some 4 degrees west of the naked eye open cluster known as the Beehive or Praesepe. Since this source is large and diffuse, any slow to medium speed meteor from anywhere in Cancer could be a candidate for this shower. The area of the sky is best placed near 0100 local standard time when it lies on the meridian and is highest in the sky.  At this time expect to see 3 shower members per hour from locations north of the equator and 1 per hour for sites south of the equator.

Unlike most of the annual showers the antihelion source is produced by debris from unknown objects orbiting in a direct motion like the earth. These objects are most likely asteroids, which produce stony and metallic debris whose density is much greater than material 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 source is active all year from an area of the sky nearly opposite that of the sun. The center of this source will move approximately one degree eastward per day and travels through many different constellations over the course of a year. It  may make sense to list these meteors as antihelions or "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. Those who share their reports with the I.M.O. should call these meteors Delta Cancrids or "DCA".

The Gamma Velids are listed among the radiants of the Dutch Meteor Society. The date of maximum activity was January 5 with a predicted ZHR of 2. Since this is a very weak shower care must be taken to exclude any sporadic activity from the Gamma Velid count. Actual observed rates should be less than 1 per hour. The radiant lies at 08:36 (129) -49. This position lies in central Vela, 6 degrees north of the 2nd magnitude star Delta Velorum. Due to the far southern declination (celestial latitude) this shower is not well seen north of the northern tropical regions. The area of the sky is best placed near 0200 local standard time when it lies on the meridian and is highest in the sky. At 35 km/sec. the Gamma Velids produce meteors of average velocity.

The Alpha Hydrids are also listed among the radiants of the Dutch Meteor Society. The date of maximum activity is January 14 with a predicted ZHR of 2. Like the Gamma Velids, care must be taken to exclude any sporadic activity from the Alpha Hydrid count. The radiant currently lies at 08:56 (134) -10. This position lies in western Hydra 8 degrees southwest of the 2nd magnitude star Alphard (Alpha Hydrae). This radiant is seen equally well from both hemispheres. The area of the sky is also best placed near 0200 local standard time. At 44 km/sec. the Alpha Hydrids produce meteors of average velocity.

The Alpha Crucids are yet another shower listed among the radiants of the Dutch Meteor Society. The date of maximum activity is January 15 with a predicted ZHR of 3. Like the previous two showers, care must be taken to exclude any sporadic activity from the Alpha Crucid count. The radiant currently lies at 12:36 (189) -62. This position lies in central Crux just 3 degrees northwest of the 1st magnitude star Acrux (Alpha Crucis). One again, due to the far southern declination this shower is not well seen north of the northern equatorial regions. The area of the sky is also best placed just before dawn when it lies highest in the sky. At 50 km/sec. the Alpha Crucids produce meteors of medium-swift velocity.

The Northern Apex source is now centered at 13:24 (201) +07. This position lies in northern Virgo some 7 degrees north of the 3rd magnitude star Zeta Virginis. This area of the sky is best placed for viewing during the last dark hour before dawn. Since this source is large and diffuse any meteors from southern Coma Berenices, southwestern Bootes or northern Virgo could be a good candidate for this shower. This source should provide at least 2 meteors per hour no matter your location.

Like the antihelion source both apex areas 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 could also be noted in some manner as to which branch of the apex complex they appear to radiate. Those who report to the I.M.O. should label these meteors as Coma Berenicids or COM.

The Southern Apex source lies exactly 30 degrees south of its northern counterpart at 13:24 (201) -23. This position lies in extreme eastern Hydra just west of the 3rd magnitude star Gamma Hydrae. 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 northwestern Centaurus, eastern Hydra or southern Virgo could a candidate from this source. Rates should be near 2 per hour from the Southern Hemisphere and 1 per hour from the Northern Hemisphere.

The Sporadic rates for the Northern Hemisphere are now slowly declining and will do so until June. One would currently expect to see perhaps 8 random meteors per hour during the last hours before dawn from rural observing sites. This estimate and the morning estimate for the Southern Hemisphere does not include the apex meteors listed above. During the evening hours perhaps 2 random meteors can be seen per hour from the Northern Hemisphere. Rates seen from the Southern Hemisphere are equal to those seen in the northern skies with perhaps 9 random meteors being seen per hour during the early morning hours and 2 per hour during the evening.  Moonlight reduces evening rates during this period.

Clear Skies!
Robert Lunsford
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