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Wiadomość od:
Robert Lunsford
International Meteor Organization
***
Meteor activity kicks into high gear in August as seen from the northern hemisphere. The main reason for all this activity is the Perseid shower that peaks on August 12. This shower is active most of the month and remains above the level of the sporadic background for a week centered on August 12. The sporadic activity is also near maximum as seen from the northern hemisphere and is now more than double the rates from just three months ago. As seen from south of the equator, meteor rates are still decent but falling rapidly. The sporadic rates continue their downward slide and the Perseid radiant does not rise high into the sky as seen in the southern hemisphere so rates from this shower are greatly reduced when compared to the northern hemisphere.

During this period the moon reaches its first quarter phase on Sunday August 3rd. At this time the moon is located 90 degrees east of the sun and will set near 2300 (11pm) local daylight time as seen from mid-northern latitudes. Later this week the waxing gibbous moon will begin to encroach into the morning sky shorting the length of time between moon set and the beginning of morning twilight. The estimated total hourly meteor rates for evening observers this week is near 3 as seen from the northern hemisphere and 2 as seen from southern tropical latitudes. For morning observers the estimated total hourly rates should be near 32 no matter your location. 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. Evening rates during this period will are lower than normal due to moonlight. Note that the hourly rates listed below are estimates as viewed from dark sky sites awa y from urban light sources. Observers viewing from urban areas will see less activity as only the brightest meteors will be visible from such locations.

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 August 2/3. 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 th ere 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.

These sources of meteoric activity are expected to be active this week:

The Kappa Cygnids (KCG) are weakly active during this period from a wide radiant located at 18:56 (284) +58. This location lies actually lies in southern Draco, 5 degrees northwest of the 4th magnitude star known as Kappa Cygni. Consider this position the center of a large radiant rather than a sharp point. Maximum activity is predicted to occur on August 18th so current rates would be less than one per hour no matter your location. With an entry velocity of 23 km/sec. most of these meteors will appear to travel slower than average. The radiant is best placed near 2300 LDT (11pm LDT) when it lies nearly overhead for much of the Northern Hemisphere. Due to its high northern declination this activity is not well seen from the southern hemisphere. Despite the low rates seen from this source, this shower is known to be a producer of fireball class meteors.

The Alpha Capricornids (CAP) are active for over a month lasting from July 6 through August 10. Unlike most showers, the Alpha Caps have a plateau-like maximum with maximum activity lasting from July 25-30. The radiant is currently located at 20:32 (308) -09. This area of the sky is located in northwestern Capricornus, 5 degrees northeast of the naked eye double known as Algiedi (Alpha Capricornii). The radiant is best placed near midnight LDT when it lies on the meridian and is highest in the sky. Rates this weekend should be near 2 per hour no matter your location. While most members of the Alpha Caps are faint, this shower has been know to produce fireballs so don't be surprised to witness an extraordinarily bright meteor from this source. With an entry velocity of 22 km/sec., the average Alpha Capricornid meteor would be of slow velocity. Please note that with this radiant and the Anthelions are located in the same area of the sky. The only way to properly differentiate betwe en them would be to have both radiants included within your field of view. Even then it could be difficult as any potential meteor could trace back to more than one radiant area, especially since the sizes of the CAP's and ANT's are larger than normal.

The center of the large Anthelion (ANT) radiant is currently located at 21:32 (323) -12. This position lies in northeastern Capricornus, 5 degrees northwest of the 4th magnitude star known as Deneb Algedi (Delta Capricorni). These meteors may be seen all night long but the radiant is best placed near 0100 LDT when it lies on the meridian and is positioned highest in the sky. Due to the large radiant area, meteors from this source may also appear to radiant from the constellation of Microscopium, southwestern Pegasus, southeastern Aquila, Aquarius, and western Pisces Austrinus as well as Capricornus. Rates at this time should be near 2 per hour no matter you location. With an entry velocity of 30 km/sec., the average Anthelion meteor would be of slow velocity.

The Delta Aquariids (SDA) are still active from a radiant located at 22:56 (344) -15. This position is located in southern Aquarius only 1 degree north of the third magnitude star known as Skat (Delta Aquarii). Hourly rates at maximum will depend on your latitude. Those viewing from the southern tropics will see the best rates of near 10-20 per hour. Rates seen from mid-northern latitudes will range from 3-10 per hour, depending on the haziness of your skies. Note that these rates will only be seen under very dark skies in rural locations during the late morning hours when the radiant lies highest above the horizon. The radiant rises near 2200 (10pm) LDT for observers located in the mid northern latitudes, but is best placed near 0300 LDT, when it lies highest in the sky. With an entry velocity of 42 km/sec., most activity from this radiant would be of average velocities.

The Piscids Austrinids (PAU) are a minor shower not well seen from the northern hemisphere. This radiant is active from July 15 through August 10. Maximum activity occurred on July 28 when the zenith hourly rate (ZHR) may reach five. These rates are only seen from the southern hemisphere where the radiant passes overhead. From mid-northern latitudes, rates of one per hour at maximum are usually seen. The radiant is currently located at 23:08 (347) -30. This position lies on the border of Piscis Austrinus and Sculptor, just 2 degrees east of the bright first magnitude star Fomalhaut (Alpha Piscis Austrinus). The radiant is best placed near 0300 LDT, when it lies highest in the sky. With an entry velocity of 35km/sec., most activity from this radiant would be of average velocities.

The Perseids (PER) are active from a radiant located at 02:16 (034) +55. This position lies in extreme western Perseus, 5 degrees west of the 4th magnitude star known as Miram (Eta Persei). The radiant is best placed during the last hour before the start of morning twilight when it lies highest in a dark sky. Since the maximum is not until August 13th, current rates would be only near 10 per hour at best, as seen from the northern hemisphere. Activity from this source is not visible south of 40 degrees south latitude. With an entry velocity of 61 km/sec., most activity from this radiant would be swift with a large percentage of persistent trains produced by the brightest meteors.

The Alpha Triangulids (ATR) are active from a radiant located at 02:40 (040) +41. This position actually lies on the Andromeda/Perseus border, 4 degrees west of the famous eclipsing variable star known as Algol (Beta Persei). This source of meteors is best seen from July 25 through August 20 with maximum activity occurring on July 27. Hourly rates should range from 1 as seen from the northern hemisphere to less than 1 as seen south of the equator. The radiant is best placed during the last hour before the start of morning twilight when it lies highest in a dark sky. With an entry velocity of 68 km/sec., most activity from this radiant would be swift.

The Eta Eridanids (ERI) are active from a radiant located at 02:30 (038) -14 . This location actually lies in southeastern Cetus, 3 degrees west of the 4th magnitude star known as Pi Ceti. I witnessed some of these fine meteors during a watch on the morning of July 30th. This shower is best seen from July 31 through August 17 with maximum activity occurring on August 4. Hourly rates should be near 3 no matter your location. The radiant is best placed during the last hour before the start of morning twilight when it lies highest in a dark sky. With an entry velocity of 66 km/sec., most activity from this radiant would be swift with persistent trains on the brighter meteors.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately 12 sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near 3 per hour. As seen from the tropical southern latitudes (25S), morning rates would be near 7 per hour as seen from rural observing sites and 2 per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Evening rates are reduced due to interfering moonlight.

Kappa Cygnids (KCG) - 18:56 (284) +58 Velocity - 27km/sec.
Northern Hemisphere - <1 per hr. Southern Hemisphere - <1 per hr.

Alpha Capricornids (CAP) - 20:32 (308) -09 22 Velocity - 22km/sec.
Northern Hemisphere - 2 per hr. Southern Hemisphere - 2 per hr.

Anthelions (ANT) - 21:32 (323) -12 Velocity - 29km/sec.
Northern Hemisphere - 2 per hr. Southern Hemisphere - 2 per hr

Delta Aquariids (SDA) - 22:56 (344) -15 Velocity - 42km/sec.
Northern Hemisphere - 5 per hr. Southern Hemisphere - 15 per hr

Piscids Austrinids (PAU) - 23:08 (347) -30 Velocity - 35km/sec.
Northern Hemisphere - <1 per hr. Southern Hemisphere - 1 per hr.

Perseids (PER) - 02:16 (034) +55 Velocity - 61km/sec.
Northern Hemisphere - 8 per hr. Southern Hemisphere - 5 per hr.

Alpha Triangulids (ATR) - 02:40 (040) +41 Velocity - 68km/sec.
Northern Hemisphere - 1 per hr. Southern Hemisphere - <1 per hr.

Eta Eridanids (ERI) - 02:30 (038) -14 Velocity - 66km/sec.
Northern Hemisphere - 3 per hr. Southern Hemisphere - 3 per hr.

***


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