Ophiuchids

Observing

The duration of this shower extends between May 19-July 2, with maximum activity falling on June 20 (λ=88°) from RA=263°, DECL=-20°. The maximum ZHR reaches 6, while the average magnitude of the meteors seems slightly fainter than 3. Less than 5% of the stream’s meteors leave persistent trains.

History

This weak shower has been with meteor observers for some time, with published observations appearing nearly every year during the 20th century. The shower’s discovery seems attributable to W. F. Denning, who, during June 14-20, 1887, plotted 5 very slow and bright meteors coming from RA=268°, DECL=-24°. The first detection of a meteor coming from this radiant seems to have been on June 8, 1841, when a fireball was listed by G. von Niessl as having originated from RA=266°, DECL=-16°.

Interestingly, the stream seems to produce a large number of bright meteors and fireballs, as the following table illustrates.

Ophiuchid Meteors and Fireballs

The first formal recognition that this shower was a producer of annual activity was in R. A. McIntosh’s “An Index to Southern Meteor Showers.” Designated as radiant 180, it was said to occur during June 14 to 21, from RA=266°, DECL=-18.5°. Another radiant, designated number 184, was named the “3 Sagittarids” and fits the observations slightly better than 180. It was said to occur during June 14-15, from RA=268°, DECL=-26°. These two radiants indicate an interesting feature displayed by this shower (and nearly all ecliptic streams, for that matter), and that is the existence of both a north and south branch.

The stream’s inclination is so small that some meteors originate above the ecliptic, while others originate below it. This has caused both radar and photographic orbits to be variously published with AOP and AN varying by 180 deg (this difference is demonstrated in the “Orbit” segment below). Despite this apparent difference in the two key angular elements, these orbits are still similar in size and shape, with the D-criterion calculation of Southworth and Hawkins recognizing that such orbits can be closely related. This is very important since such orbital differences might be due more to inaccurate data than to natural orbital evolution. A similar conclusion was suggested by Bertil-Anders Lindblad in 1971, after noticing several ecliptic streams were being split into northern and southern branches by computer analysis. Most photographic meteors and visual meteors of this stream tend to come from the radiant north of the ecliptic.

Recent observations of this shower indicate weak, but consistent activity. During 1971, Meteor News published the results of 38 hourly rates reported by 7 observers in Australia and the United States. Between June 15.2 and June 21.2, rates rose slowly to a maximum of 8 per hour, then rapidly fell off to values of 0 to 1 per hour during June 22.2 to 27.2. This rate of 8 per hour might better represent what activity levels would be like in the Southern Hemisphere since observations from Australia were included. Estimates by observers in the United States reveal values of 1 to 2 per hour on the night of maximum during the years of 1972 to 1985. In addition, activity levels do tend to be significantly lower before and after the date of maximum. The British Astronomical Association lists the ZHR of this shower as 6.

The only major study of this stream to reveal other details besides hourly rate estimates was made in 1978 by observers of the West Australia Meteor Section. A total of 70 shower members were detected. The average magnitude was determined to be 3.25 and 4.3% of the meteors showed persistent trains.

This meteor shower is considered one of the candidates for possible association with periodic comet Lexell (1770 I). The Ophiuchid orbit does not perfectly match that of the comet, but the very low inclination would allow very small planetary perturbations to vary the AOP and AN, by large amounts. According to Porter, the probable date of maximum activity from a stream associated with the comet would be July 5, at a radiant of RA=272 deg, DECL=-21 deg.

Orbit

During the Radio Meteor Project conducted by Z. Sekanina during 1968-1969, a total of 28 meteors indicated the following orbit (north branch?):

During the Southern Hemisphere Radio Survey, conducted by C. S. Nilsson during 1960-1961, the following orbit was revealed (south branch?):

Sekanina’s radar orbit was based on 28 radio meteors, while Nilsson’s was based on only 3. If the assumption that a lack of precise data is responsible for orbits such as Nilsson’s, then Sekanina’s orbit should be considered as the proper orbit for this stream. Most of the visual radiants fit Sekanina’s orbit better than Nilsson’s. Nilsson pointed out that the node “could in fact be descending, not ascending.”

The orbit of comet Lexell (1770 I) is listed in B. G. Marsden’s Catalog of Cometary Orbits (1983) as follows: