This shower is active during the period of June 2-July 29. Reaching maximum
around June 27 (Solar Longitude=95 deg), the average radiant at that time is
RA=278 deg, DECL=-4 deg. The hourly rate is probably 2-4.
History
The discovery of this meteor shower should be credited to R. A. McIntosh,
since it was listed in his classic work "An Index to Southern Meteor Showers".
Designated radiant number 191 and referred to as the "Eta Serpentids I," the
radiant was based on 3 visual radiants. Its duration was given as June 25-30,
and the radiant was shown to move from RA=274 deg, DECL=-6 deg to RA=277 deg,
DECL=-3 deg. Unfortunately, since the radiant was literally buried amidst 320
other radiants, no apparent searches were made to confirm the shower.
More official recognition of this stream came in 1971, when a computerized
stream search among photographic meteor orbits by Bertil-Anders Lindblad
revealed a radiant at RA=278 deg, DECL=-2 deg, during the period of June 25 to
July 3. Referred to as the "Eta Serpentids," this stream was based on only 2
meteor orbits, but Lindblad noted a similarity to radiants previously noted by
R. A. McIntosh and William F. Denning (to be discussed below).
The first person to finally establish the shape of the orbit and duration of
the shower was Zdenek Sekanina during the Radio Meteor Project conducted at
Havana, Illinois, during 1961-1965. During the period between June 17 and July
15, 7 meteors were noted from an average radiant of RA=276.3 deg, DECL=-6.3 deg.
The estimated date of maximum was June 24.7. Sekanina confirmed the stream's
existence during the 1968-1969 revival of the Radio Meteor Project. On this
occasion, 32 meteors were detected during the period of June 2 to July 29. The
average radiant was found to be RA=280.7 deg, DECL=+1.0 deg, while the date of
maximum was more clearly determined as June 27.0.
A search for older records of this stream reveals only two possibilities in
the 19th century. Both of these radiants were detected by the Italian Meteoric
Association and were evaluated by William F. Denning, who concluded that 20
meteors detected during June 25-30, 1869-1872, indicated a radiant at RA=275
deg, DECL=-9 deg. Another 20 meteors observed during June 26 to July 11, 1872,
indicated a radiant at RA=273 deg, DECL=-2 deg. Neither of these radiants
(designated 211-2 and 211-3, respectively) provide positive proof of the
existence of the June Scutids prior to the 20th century, but they do barely
qualify as being associated, according to the D-criterion.
Additional 20th Century observations have been found in Cuno Hoffmeister's
book Meteorstrome (1948), which lists 5 German-observed radiants from this
stream. The first observation came on June 29, 1912 (Solar Longitude=97.0 deg),
when several meteors were plotted from RA=281 deg, DECL=-3 deg. Two apparent
observations were made in 1935, when radiants were determined on June 23 (RA=272
deg, DECL=-1 deg) and June 26 (RA=277 deg, DECL=-10 deg). Another observation
was made on June 25, 1936, when meteors were plotted from RA=270 deg, DECL=+4
deg. The final German observation came on July 4, 1937, when a radiant of RA=276
deg, DECL=+4 deg was detected.
The Author has observed meteors from this shower since July 6/7, 1973, and
he has managed to continue to observe members of this stream during the period
of June 24 to July 7, at a rate of 0.5 to 1 per hour, up to the present time. On
June 29, 1986, he was finally able to actually observe on the night of maximum.
In one hour, 4 meteors were plotted from RA=277 deg, DECL=-3 deg. Other
observations acquired that year allowed the shower's average magnitude to be
estimated as 2.5 (limiting zenithal magnitude=5.5).
Orbit
The radar orbit determined in 1969, by Sekanina during the Radio Meteor
Project, is based on 32 meteors and is as follows: