eta-Aquarids 2000

The meteor shower of the eta-Aquarids is not easily observed from mid-northern latitudes where the majority of visual observers is located, because of the very late rising of the radiant before dawn, and fewer amateurs are observing from the southern hemi- sphere where dawn is much later, and the radiant climbs higher before the end of the meteor watch.

It is therefore even more challenging to produce a meaningful activity graph of the eta-Aquarids quickly after their maximum, and I am very grateful for the immediate submission of the reports by the observers, which are stated at the end of this post.

The gradual increase of activity is nicely show in the below Table. The maximum time is, however, hard to fix because of a severe dip in the UT morning of May 6 when the ZHR fell below half-value of its neighbours. Maximum ZHRs appear to be at the lower end of previous years' typical values of 60-70 per hour.

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Date   Time (UT)  Sol.  nETA  nObs  ZHR    +/-
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Apr 29   1800    39.71    1    2     2.4   1.7
Apr 30   1640    40.63    2    1    20    11
May 01   1730    41.64   25    3    24     4.8
May 03   0050    42.90   23    4    36     6.1
May 04   0840    44.19   15    3    38     9.5
May 04   1750    44.56   14    4    50    13
May 05   1330    45.35   80    5    49     5.5
May 06   0530    46.00   12    5    24     6.8
May 06   1610    46.43  119    6    51     4.7
May 07   0530    46.96   19    4    25     5.7
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Solar longitudes refer to equinox J2000. Average times are given with 10-minute accuracy though often refer to many hours coverage. The average ZHR was computed by <ZHR> = sum n / sum(Teff/C) where Teff is the effective observing time, C is the total correction according to limiting magnitude, possible field obstruction and radiant elevation as sin(hR). The ZHR refers to a limiting magnitude of +6.5 and a radiant elevation of 90 degrees. nETA is the number eta-Aquarids seen, nObs is the number of observing periods contributing to the average; the number of individual observers is smaller in most of the cases.

I am very greatful to the following observers for their submission and therefor contribution to this article:

DAVMA Mark Davis (USA), JOHCA Carl Johannink (the Netherlands), LANMA Marco Langbroek (the Netherlands), LINMI Mike Linnolt (USA), MARAD Adam Marsh (Australia), MARPI Pierre Martin (Canada), MATMI Michael Matiazzo (Australia), MCLAL Alex M'clintock (Spain), MISKO Koen Miskotte (the Netherlands), MOSSC Scott Moser (USA) and YOUKI Kim Youmans (USA).