Alpha Pisces Australids

Observing

The duration of this southern shower extends from July 16 to August 13. Maximum occurs on July 30 (λ=127°), at which time the radiant is at α=337°, δ=-28°. The maximum ZHR tends to reach 3-5. The meteors are generally slow and white.

History

This meteor shower was plainly observed on several occasions during the 19th Century and into the 20th Century, but, despite the numerous observations, the stream was virtually ignored during the period of 1938-1952.

The discovery seems best attributable to Alexander S. Herschel, who observed a radiant of α=338°, δ=-28° on July 28, 1865. The first apparent confirmation was made by E. F. Sawyer (Cambridge, Massachusetts), who plotted four very slow and bright meteors from a radiant of α=337°, δ=-33° on July 28, 1878. Other observations were made by Cruls (Rio de Janeiro Observatory) during July 25-30, 1881, when several meteors were detected from α=343°, δ=-25°, and by W. F. Denning during July 28-31, 1898, when four slow and white meteors were plotted from α=338°, δ=-25°. As can be seen, only Cruls' observation was from the Southern Hemisphere, so that the other three observers isolated the radiant even though it was at a low altitude of 20 deg or less. During the first four decades of the 20th Century, two major groups of observers---one in Germany and the other in New Zealand---shed new light on this stream's duration and radiant.

In his 1948 book Meteorstrome, C. Hoffmeister separated the 5406 German-observed visual radiants into two separate groups and managed to detect the Alpha Pisces Australids in each collection. The first detection involved 10 radiants observed during the period of 1910-1930. The average radiant was given as α=336°, δ=-28°, while the date of maximum was given as July 29 (λ=125°). From the second group of radiants the shower was again detected. Primarily involving observations obtained in 1937, when Hoffmeister was observing in South Africa, the average radiant was given as α=338°, δ=-29°, while the date of maximum was given as August 2 (λ=129°). After combining all of the shower's radiants, Hoffmeister concluded that the stream produced notable activity during July 29-August 2 from an average radiant of α=337°, δ=-28°. The date of maximum was given as July 31 (λ=127°). Hoffmeister added that the simultaneous rise and fall of activity from this stream and the Delta Aquarids, as well as the large apparent radiant of the latter shower, brought to light the possibility of an association.

Using observations made by New Zealand observers during the 1920's and early 1930's, Ronald A. McIntosh found seven apparently separate areas of activity from the relatively small constellation of Pisces Austrinus which reached maximum at different times between mid-July and mid-August. The most prominent shower was called the "Alpha Pisces Australids" (the same name Denning gave to the 19th Century observations), the existence of which was based on 24 visual radiants. The duration was given as July 26-August 8, during which time the radiant moved from α=337°, δ=-33° to α=350°, δ=-30°. The other six radiants isolated by McIntosh are as follows:

  • Pisces Australids: Based on 3 visual radiants, the duration was given as July 28-August 3, while the average radiant was at α=326°, δ=-26°.
  • Theta Pisces Australids: Based on 2 visual radiants, the duration was given as August 12-14, while the average radiant was at α=327°, δ=-32°.
  • Beta Pisces Australids: Based on 11 visual radiants, the duration was given as July 14-22, while the average radiant moved from α=330.5°, δ=-30° to α=339°, δ=-30°.
  • Lambda Pisces Australids: Based on 5 visual radiants, the duration was given as August 5-14, while the average radiant moved from α=334°, δ=-27.5° to α=339°, δ=-26°.
  • Epsilon Pisces Australids: Based on 3 visual radiants, the duration was given as August 13-14, while the average radiant was at α=338°, δ=-24°.
  • 20 Pisces Australids: Based on 2 visual radiants, the duration was given as August 8-9, while the average radiant was at α=340.5°, δ=-27°.

As noted earlier, there is a period of complete neglect of this meteor shower following the 1937 observations of Hoffmeister's group, but observations were finally resumed in 1953. In that year, radar equipment at Christchurch, New Zealand observed a "highly probable" Pisces Australid radiant at α=328°, δ=-27° during July 21-26. The shower was considered quite strong.

During 1960, a more elaborate radar survey was conducted by B. L. Kashcheyev and V. N. Lebedinets at the Kharkov Polytechnical Institute (USSR). They detected 32 meteors from this stream during July 16-August 13, and concluded that maximum came on July 26 (solar longitude=123 deg), at which time the radiant was at α=340°, δ=-26°. From this data, the first orbit was computed which indicated a 45 deg inclination and a semimajor axis of 4.31 AU.

The long absence of visual observations finally ended in 1965, when Edward F. Turco (Cranston, Rhode Island), a member of the American Meteor Society, observed the Alpha Pisces Australids during three nights, centered on July 29/30. "The meteors I saw were not too bright, though I was surprised with two exceptions, both fireballs." He pointed out that this was the first time he had ever detected this shower.

The fact that Turco only noted the shower in 1965, despite being a regular observer, as well as member and regional director of the American Meteor Society for many years, brings forth an excellent explanation as to the reason for the shower's neglect during 1938-1952. Meteors from this shower are only visible from the United States and Europe under special circumstances that not only involve weather, but also require an unusual number of meteors heading toward the north. Observers in the Southern Hemisphere should find the shower as an annual fixture in their late July skies. It will be remembered that Hoffmeister noted excellent activity from this radiant during his observations in South Africa in 1937, and McIntosh noted numerous radiants in the area based upon observations made by him and fellow New Zealand observers during the 1920's and 1930's.

The first notable Southern Hemisphere visual survey of meteor activity following that of McIntosh, was conducted by Michael Buhagiar (Perth, Western Australia) during 1969-1980. Recording a total of 20,974 meteors, Buhagiar compiled a list of 488 probable visual radiants. Radiant 472 was called the "Alpha Pisces Australids" and was based on 10 visual radiants determined during the 12-year period. The duration was given as July 27-August 10, while a maximum hourly rate of 4 was said to be emanating from α=344°, δ=-30° on July 31. None of the nearby Pisces Austrinus radiants noted by McIntosh were prominent enough to make Buhagiar's list.

Nearly simultaneous with Buhagiar's survey, the Royal Astronomical Society's New Zealand Meteor Section was also conducting a decade-long survey for a list of Southern Hemisphere meteor showers. Covering the 1970's, the observations allowed section director J. E. Morgan to compile a list of 213 probable visual radiants. The "Alpha Pisces Australid" shower was detected as usual. The duration was given as July 23-August 2, during which time the radiant moved from α=344°, δ=-31° to α=347°, δ=-34°. The maximum ZHR was given as 4. Interestingly, McIntosh's "Beta Pisces Australid" shower was also detected by the New Zealand observers. Given a short duration of July 19-21, the average radiant was at α=337°, δ=-34°, while the maximum ZHR was 3. Another radiant was also found which seems closely related to the McIntosh's August portion of the Alpha Pisces Australids. Called the Xi Gruids, their duration was given as July 24-August 8, during which time the radiant moved from α=343°, δ=-32° to α=350°, δ=-32°.

Since 1977, the Western Australia Meteor Section (WAMS), under the directorship of Jeff Wood, has been extremely active. The Alpha Pisces Australids were observed during July 23-29, 1977. A maximum ZHR of 3.65+/-2.11 was observed on July 28, at which time the radiant was located at α=343°, δ=-30°. During 1979 meteors were observed from this shower during July 27-August 5. A maximum ZHR of 3.82+/-0.52 came on July 28 from an average radiant of α=343°, δ=-28°. A full moon occurred on July 27, 1980, thus interfering with complete observations of this shower maximum. However, observers still gave the shower's duration as July 19-August 4, and detected a maximum ZHR of 2.00+/-0.33 on August 3. The average radiant was then given as α=336°, δ=-32°, and the Author believes this indicates the 1980 observations were a conglomeration of several showers in the region.

Orbit

The orbit of the Alpha Pisces Australid stream, as determined by Kashcheyev and Lebedinets, is as follows:

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The Author has located one photographic meteor among the more than 2000 orbits obtained during the Harvard Meteor Project of 1952-1954. It is listed in MP1961 and was designated 3443. It was detected on July 28, 1952, from α=338°, δ=-27°.

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131305420.190.987.50

The Author has also looked through the 39,145 radio meteor orbits obtained by Zdenek Sekanina during the two sessions of the Radio Meteor Project conducted during the 1960's. Five meteors were located, which indicated a duration of July 24-30. The stream seems to cross its ascending node on July 29, with an average radiant of α=341.9°, δ=-26.9°. The orbit follows:

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137.8305.139.90.1860.8931.743