Meteor Showers Online

Gamma Normids (GNO)

Ronald A. McIntosh (Auckland, New Zealand) discovered this meteor shower on March 10.1, 1929. He plotted seven meteors which indicated a radiant of α=241.5 deg, δ=-43 deg. Confirmation came in 1932, when Murray Geddes (New Plymouth, New Zealand) plotted six meteors on March 7.1, from α=242.7 deg, δ=-54.7 deg. Geddes plotted another five meteors on March 12.0—the radiant then being α=240 deg, δ=-52 deg. McIntosh summarized these radiants in his 1935 paper “An Index to Southern Meteor Showers.” The duration was given as March 7-12, and the weighted average radiant was α=241 deg, δ=-53 deg. It was referred to as the “Scorpiids.”

This stream were virtually ignored until 1953, when radar equipment used by A. A. Weiss (University of Adelaide, South Australia) accidentally detected activity on March 15-16. Although the radiant position was estimated as α=250 deg, δ=-50 deg, Weiss said it could not “be fixed precisely because of low activity and also because of the marked deficiency of large meteors in this stream.” He elaborated by noting that the number of radar echoes with a duration of one-half second or longer were practically no greater during the shower than on non-shower days. Weiss also indicated that the radiant’s culmination after sunrise would make visual observations difficult.

Curiously, C. D. Ellyett and C. S. L. Keay (Christchurch, New Zealand) made an attempt to confirm this shower during March 1956. The equipment was set at the same sensitivity as Weiss’ during March 8-14, and it was set at a higher sensitivity during March 15-23, but neither session revealed the shower. The authors concluded the shower “is variable in activity from year to year.”

The next observation of the Gamma Normids came during March 16-22, 1969, while G. Gartrell and W. G. Elford operated the radio meteor system at Adelaide, South Australia. Two associations were noted which possessed radiants close to that of this stream. The first was based on three meteor orbits and possessed a radiant position of α=250 deg, δ=-43 deg on a mean date of March 20. The second association was considered less reliable since it was based on only two meteors. Its radiant was α=253 deg, δ=-41 deg on a mean date of March 19.

M. Buhagiar (Perth, Western Australia) published a list in 1981, which gave details of meteor showers observed by himself during 1969-1980. Radiant number 339 (called the “Beta Arids”) was given a duration of March 15-21. Maximum was said to have occurred on March 17, from α=245 deg, δ=-50 deg. The maximum hourly rate was given as 4.

Observers of the Western Australia Meteor Section (WAMS) have contributed greatly to observations of this shower in recent years. During 1979, the Gamma Normids were observed over the period of March 16-18. Maximum came on March 17, when a ZHR of 8.45+/-1.60 was detected from α=248 deg, δ=-49 deg. In 1980, observations were made during March 14-15. At maximum on March 15, the ZHR was 8.90+/-2.30 and the radiant was α=242 deg, δ=-50 deg.

The WAMS made very extensive observations during 1983. The earliest Gamma Normid activity came on the night of March 10/11, when the ZHR was about 1.5+/-0.3. After another low ZHR of 1.6+/-1.0 on March 11/12, a sharp rise to a ZHR of 9.6+/-2.3 came on March 13/14, followed by a rate of 4.6+/-0.6 on March 14/15. Thereafter, rates were 2.2+/-0.8 on March 15/16, 0.5+/-0.1 on March 17/18, and 0.7+/-1.1 when last seen on March 18/19. Based on 63 meteors, the average magnitude was determined as 2.68, while 9.5% had trains. For the meteors of magnitude 2 or brighter, 64% were white, 24% were yellow, 8% were orange, and 4% were blue.

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