Alpha Hydrids

Observing

The duration of this shower extends from January 15 to 30. At maximum on January 20, meteors can be expected to reach an hourly rate of 2-5 from a radiant of α=140°, δ=-9°.

History

The first apparent observation of this shower was made by Ronald A. McIntosh on January 15, 1929. Four plotted meteors revealed a radiant of α=132.2°, δ=-7.0°. The shower does not appear in any records prior to the 20th century, nor in the major radiant catalogs of E. Öpik (1934) and C. Hoffmeister (1948). McIntosh's observation remained the only detection of this shower by Southern Hemisphere observers up to 1935, so that it was not included in his "An Index to Southern Meteor Showers," which appeared in the Monthly Notices of the Royal Astronomical Society in that year.

The first determination of this shower's hourly rate was made during January 20/21 and 24/25, 1971, by three members of the American Meteor Society. K. Simmons (Florida), J. West (Texas) and T. Recascino (New Jersey) detected maximum rates of 2-3 during this period when the limiting magnitude was 5.5-6.0.

Perhaps the greatest knowledge of this meteor shower has come from the observations of the Western Australia Meteor Section (WAMS) made during the period of 1979 to 1986. During that first year, observers detected Alpha Hydrids during January 20-30, and determined the date of maximum as January 25. The average radiant was α=140°, δ=-9°, while the maximum ZHR was given as 8.51+/-1.84. Other details uncovered included an average magnitude of 3.15 (based on 54 meteors) and the fact that 10.2% of the meteors left trains. The meteors also tended to display three colors: 56.2% were white, 37.5% were yellow and 6.3% were blue. During 1980, Alpha Hydrids were detected during January 12-27, with a maximum ZHR of 1.90+/-0.19 occurring on January 16 from α=136°, δ=-10°. The hourly rates indicated possible irregular activity coming from this radiant. Observations in the following years revealed this to be true, with hourly rates barely attaining 2 per hour during 1982, 1984 and 1986, while rates reached 4-5 in 1983 and 3-4 in 1985.

Members of the WAMS succeeded in determining a series of radiant positions during 1980, which display a definite eastward movement. Using only those days for which 2 or more positions could be averaged, the Author determined four positions: RA=133°, DECL=-10° on January 16/17, α=138.8°, δ=-10.3° on January 18/19, α=141°, δ=-9° on January 22/23, and α=146°, δ=-10° on January 26/27.

The Author has sought to determine the orbit of this stream and has succeeded in finding 2 photographic members in papers published in 1961 and 1973 and 19 radio members in a paper published in 1986. Two apparent streams were revealed. The first radiant is composed of 4 radio meteors and the 2 photographic meteors and is apparently responsible for the visual activity. The duration is January 10-28. The nodal passage comes on January 17, with the radiant then being at α=135.9°, δ=-10.0°. The radiant's daily motion is +0.98° in α and -0.57° in δ. The other stream is made up of 15 radio meteors and is active during January 11-30. The nodal passage occurs on January 21 from α=149.0°, δ=-9.1°. The daily motion is +0.88° in α and -0.51° in δ. It is possible that, since the radar data never adequately covered the period of January 20-25, the maximums of both streams may occur later than the indicated dates of the nodal passages.