THE APRIL-LYRIDS

Appearances of the April Lyrid meteor shower have been recorded since as far back as 687 BC. However, in most years the shower is of very low activity, but with bursts of activity at least one order of magnitude higher than normal, occurring at time intervals of about 12 yr. Since the orbital period of the parent comet is far in excess of 12 yr, the explanation for these outbursts cannot be simply in terms of a burst of activity being seen every time the comet is close to the Earth. In this paper we investigate various mechanisms that could be responsible for this activity, but find no explanation other than ones where the degrees of freedom in the models are equal to the number of facts to be explained.