(meteorobs) Meteor Activity Outlook for May 12-18, 2012

[Robert Lunsford]

During this period the moon reaches its last quarter phase on Saturday the 12th. At this time the moon will be located ninety degrees west of the sun and will rise near 0100 local daylight time (LDT). As the week progresses the waning crescent moon will rise later in the morning, increasing the window of opportunity to view in totally dark conditions. The estimated total hourly rates for evening observers this week is near three for observers in the northern hemisphere and four for those south of the equator. For morning observers the estimated total hourly rates should be near nine as seen from mid-northern latitudes and fifteen from mid-southern latitudes. 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. Morning rates are reduced slightly due to moonlight during this period.

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 May 12/13. 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 large Antihelion (ANT) radiant is currently located at 16:16 (244) -21. This position lies in northwestern Scorpius, six degrees northwest of the bright first magnitude orange star Antares (Alpha  Scorpii). Due to the large size of this radiant, Antihelion activity may also appear from western Ophiuchus, Libra, northern Lupus, as well as Scorpius. This radiant is best placed near 0200 LDT, when it lies on the meridian and is located highest in the sky. Rates at this time should be near one per hour as seen from the northern hemisphere and two as seen from south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of slow velocity.

The last of the Eta Lyrids (ELY) are visible this weekend from a radiant located at 19:23 (292) +43. This position lies in extreme eastern Lyra, four degrees southwest of the third magnitude star Delta Cygni. This shower is active from May 6 through the 14th and peaked on May 11. Rates at maximum activity are near two per hour as seen from the northern hemisphere. Unfortunately the Eta Lyrid radiant does not rise very high in the northern sky as seen from the southern hemisphere so rates seen from below the equator are minimal. Activity from this shower is best seen during the last hour before dawn when the radiant is situated highest in a dark sky. With an entry velocity of 43 km/sec., the average Eta Lyrid meteor would be of medium speed.

The Eta Aquariids (ETA) are particles from Halleys Comet, produced in Earth-crossing orbits many centuries ago. We pass closest to these orbits from May 5 through the 9th. During this period the Eta Aquariids are at their best, capable of producing ZHRs of sixty. The actual visible rates are most often less than half this figure due to the low altitude of the radiant at dawn. Observed hourly rates at maximum normally vary from zero at 60 degrees north latitude to 30 near the equator and back down to near zero again in Antarctica, where the radiant elevation is again very low. Hourly rates this weekend will most likely be less than five per hour. Rates will slowly decrease as the week progresses as we move further from the May 7 maximum. The radiant is currently located at 22:52 (343) +01. This area of the sky is located on the Aquarius/Pisces border, three degrees east of the fourth magnitude star Eta Aquarii. The best time to view this activity is during the hour before the start of morning twilight, when the radiant lies highest in a dark sky. With the moon now in the morning eastern sky, it would be best to face either due north or due south, just enough to keep the moon out of your field of view. With an entry velocity of 67 kilometers per second, a majority of these meteors will appear to move swiftly with a high percentage of the bright meteors leaving persistent trains. Surprisingly, this shower produces very few fireballs.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately four 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 eight 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. Morning rates are reduced due to moonlight.

The table below presents a condensed version of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning.

Antihelion (ANT) - 16:16 (244) -21   Velocity 30km/sec
Northern Hemisphere - 1 per hr Southern Hemisphere - 2 per hour

Eta Lyrids (ELY) - 19:23 (292) +43   Velocity 43km/sec
Northern Hemisphere - 1 per hr Southern Hemisphere - <1 per hour

Eta Aquariids (ETA) - 22:52 (343) +01   Velocity 67km/sec
Northern Hemisphere - 3 per hr Southern Hemisphere - 5 per hour

Clear Skies!
Robert Lunsford
American Meteor Society