(meteorobs) Meteor Activity Outlook for July 28-August 3, 2012

[Robert Lunsford]

During this period the moon reaches its full phase on Wednesday August 1st. At this time the moon will be located opposite the sun and will be above the horizon all night long.This weekend the waxing gibbous moon will set during the late morning hours, allowing a short window of opportunity to view activity under dark skies. The estimated total hourly meteor rates for evening observers this week is near four no matter your location. For morning observers the estimated total hourly rates should be near twenty six from the mid-northern hemisphere and twenty eight from the mid-southern hemisphere. 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 are reduced due to moonlight.

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 July 28/29. 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 radiants are expected to be active this week:

A new source found by the IMO video cameras to be active this time of year are the July Zeta Draconids (ZED). This radiant has been found to be active from July 19-29 with maximum activity activity occurring on the 19th. The last of these meteors may be seen this weekend from a radiant located at 18:06 (271) +62, which is situated in southern Draco, eight degrees southeast of the third magnitude star Al dhibain (Zeta Draconis). Due to a low amount of data the mean position of activity shifts quite a bit night to night so consider this a wide radiant until better parameters can be obtained. Current rates would most likely be less than one per hour no matter your location. The radiant is best placed near 2200 (10pm) LDT when it lie highest above the horizon. With an entry velocity of 23 km/sec., the average July Zeta Draconid meteor would be slow.

Another new source found by the IMO video cameras to be active this time of year is the July Gamma Draconids (GDR). This radiant has been found to be active from July 24-31, with maximum activity occurring on the 28th. Unfortunately the bright, waxing gibbous moon is above the horizon when this source is best placed in the sky. Therefore rates would most likely be less than one per hour no matter your location. The radiant is currently located at 18:42 (281) +51, which is locate six degrees east of the second magnitude star Eltanin (Gamma Draconis). The radiant is best placed near 2300 (11pm) LDT when it lie highest above the horizon. With an entry velocity of 27 km/sec., the average July Gamma Draconid meteor would be slow.

The Alpha Capricornids (CAP) are active from a wide radiant located at 20:18 (305) -11. This position lies in northwestern Capricornus, only one degree north of the third magnitude double star Alpha Capricornii. The radiant is best placed near 0100 local daylight time (LDT), when it lies on the meridian and is highest in the sky. Maximum activity is expected on the 29th so current rates should be near two per hour under dark skies. Don't confuse these meteors with the antihelion meteors, which have a radiant just to the east. Both radiants need to be in your field of view to properly sort these meteors. With an entry velocity of 25 km/sec., most activity from this radiant would be slow, a bit slower than the antihelions. This radiant is well seen except for far northern latitudes where it remains twilight all night long and the radiant does not rise as high into their sky.

The large Antihelion (ANT) radiant is currently located at 21:12 (318) -14. This position lies on the Capricornus/Aquarius border, two degrees northwest of the fourth magnitude star Iota Capricorni. Due to the large size of this radiant, Antihelion activity may also appear from southern Aquila, Microscopium, eastern Sagittarius, Aquarius, and Piscis Austrinus as well as Capricornus. 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 are expected to be near one per hour as seen from the northern hemisphere and two per hour 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 Delta Aquariids (SDA) reach maximum activity on the 29th from a radiant located at 22:42 (340) -16. This position is located in southwestern Aquarius, three degrees west of the third magnitude Delta Aquarii. Hourly rates will depend on your latitude and time of night. Unfortunately the moon will be above the horizon when the radiant culminates near 0300 LDT. During the last hour of darkness rates should range from fifteen shower members as seen from the southern hemisphere to less than five as seen from high northern latitudes. 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 occurs 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 22:48 (342) -29. This position lies in eastern Piscis Austrinus, three degrees southwest 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 01:46 (027) +54. This position lies on the Cassiopeia/Perseus border, five degrees east of the fourth magnitude star Theta Cassiopeiae. 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 12th, current rates would be only three to four 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.

Another new source found by the IMO video cameras to be active this time of year are the Alpha Triangulids (ATR). This radiant has recently been found to be active later than previously published, with the activity period ranging from July 25 through August 21 with maximum activity occurring on July 27. Current rates would be near one per hour as seen from the northern hemisphere and less than one from the southern hemisphere. The radiant is currently located at 02:02 (031) +40, which is actually situated in eastern Andromeda, three degrees south of the famous second magnitude star double star Almach (Gamma Andromedae). The radiant is best placed during the last hour before dawn, when it lies highest in a dark sky. With an entry velocity of 67 km/sec., the average Alpha Triangulid meteor would be swift.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately twelve 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 seven per hour as seen from rural observing sites and one per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Evening 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 .

July Zeta Draconids (ZED) - 18:06 (271) +62   Velocity 23km/sec
Northern Hemisphere - <1 per hr   Southern Hemisphere - <1 per hour

July Gamma Draconids (GDR) - 18:42 (281) +51   Velocity 27km/sec
Northern Hemisphere - <1 per hr   Southern Hemisphere - <1 per hour

Alpha Capricornids (CAP) - 20:18 (305) -11   Velocity 25km/sec
Northern Hemisphere - 2 per hr   Southern Hemisphere - 2 per hour

Antihelions (ANT) - 21:12 (318) -14   Velocity 30km/sec
Northern Hemisphere - 1 per hr   Southern Hemisphere - 2 per hour

Delta Aquariids (SDA) - 22:42 (340) -16   Velocity 42km/sec
Northern Hemisphere - 5 per hr   Southern Hemisphere - 12 per hour

Piscids Austrinids (PAU) - 22:48 (342) -29   Velocity 35km/sec
Northern Hemisphere - 1 per hr   Southern Hemisphere - 3 per hour

Perseids (PER) - 01:46 (027) +54   Velocity 61km/sec
Northern Hemisphere - 4 per hr   Southern Hemisphere - 2 per hour

Alpha Triangulids (ATR) - 02:02 (031) +40   Velocity 67km/sec
Northern Hemisphere - 1 per hr   Southern Hemisphere - <1 per hour

Clear Skies!
Robert Lunsford
American Meteor Society