Alpha Ursa Majorids

Observing

This meteor stream seems to produce a weak meteor shower during August 9 to 30. The maximum occurs during August 13 to 14, from an average radiant of α=165°, δ=+63°, and tends to produce meteors at the rate of 4 per hour. There is evidence that this shower may be strong telescopically and with radar, but few details are available.

History

This stream is relatively new in the observational records. It was discovered by W. A. Feibelman while observing the Perseids in 1961. He claimed that between “3:00 and 5:00 a.m. E.D.T. on August 14/15, four meteors per hour were seen to radiate from the direction of Alpha Ursa Majoris toward the zenith.” Rates of one per hour persisted during the next two nights. The meteor paths were typically 20° to 30° long and the velocity, compared to the Perseids, was considered low. Feibelman added, “There were no terminal bursts, and the light intensity tapered off gradually.”

Apparent confirmation came from the Mt. Bezovec meteor expedition, led by Z. Kviz and J. Kvizova. During August 6 to 17, 1961, three groups of eight observers were using the independent counting method to “determine the meteor perception probability.” Although radiants were not computed from the data, the direction of motion could be established and an increase in meteor activity was noted from the region of Alpha Ursa Majoris on the evenings of August 13/14 and 14/15.

Attempts by the Author to track down visual activity from this stream prior to 1961 have been unsuccessful. No trace of this shower appears in the extensive radiant lists of the American Meteor Society, nor in lists published in Britain, Germany and Russia. On the other hand, one photographic meteor was found. On August 17, 1952, cameras of the Harvard Meteor Project photographed a -0.1-magnitude meteor that originated from a radiant of α=169°, δ=+65°. The orbit is listed below.

Whether the meteor shower was in existence prior to 1961, seems uncertain at present. However, one source seems to indicate that the shower persisted after 1961. The Author has examined the 39,145 radio meteors obtained by Z. Sekanina during the two sessions of the Radio Meteor Project of the 1960’s, and has isolated 27 radio meteor orbits. Although the existence of such a shower was missed by the initial computer search carried out by Sekanina, it is not the first to have been missed and its significance does not readily appear until both lists are compared.

The data presented is indeed scanty and, if not for the radio-echo meteor data, the shower would not have been included in this book. Nevertheless, it is interesting to note that during the five years of sensitive radio-echo data, meteors were detected each year, so that the stream may at least be considered a possible producer of an annual telescopic meteor shower. The visual information obtained by Feibelman is also interesting, but may simply represent an outburst of activity.

Finally, there is one other point that must be added which could explain the shower’s visual appearance in 1961. The orbit of this meteor stream is very similar to that of comet Alcock (C/1959 Q1). Although the orbit of this comet is not considered a meteor producer in a list compiled by J. Drummond in 1981, the fact that the meteors are predominantly small, and more susceptible to perturbations than larger meteors, could explain the stream’s smaller perihelion distance and subsequent encounter with Earth. The unusual outburst of bright meteors that appeared in 1961, may have been directly due to a cloud of material following comet C1959 Q1.

Orbit

Thus far, the photographic records of meteors have revealed only one rough orbit. That orbit, which comes from a survey by McCrosky and Posen, is as follows:

A more precise orbit was determined by the Author from 27 radio meteors extracted from the 39,145 radio meteor orbits obtained by Sekanina during the Radio Meteor Project. The average orbit is as follows:

Finally, for the sake of comparison, the orbit of comet Alcock (C/1959 Q1) is also given. The agreement between the angular orbital elements is excellent.