Update (11 June 2013): it looks like no outburst was seen. The meteor shower will remain elusive for another while...
On 11 June 1930, three meteor observers in Maryland (USA) witnessed a flurry of shooting stars originating from the constellation of Delphinus. The mysterious meteor shower, called the gamma-Delphinids, lasted less than 30 minutes. The shower had never been seen before, and it has never returned since... until this year?
The gamma-Delphinids are one of a dozen rare meteor showers for which only anecdotal evidence exists. Such showers are thought to be caused by the dust trails of unknown long-period comets.
Meteoroid streams from long-period comets are thought to be very narrow. In fact the dust trails are so compact that our planet only encounters them when the gravitational pull from Jupiter and Saturn steers the stream exactly into Earth's path. In contrast, famous meteor showers such as the Perseids and the Leonids originate from known short-period comets. Such streams are more widely dispersed due to their frequent exposure to planetary perturbations and solar radiation in the Solar System, and hence Earth encounters those short-period streams every year.
On 11 June 2013 near 8:30 UT, Earth is predicted to encounter the gamma-Delphinids for the first time since 1930. By measuring the time of the outburst, or its absence, we'll be able to establish whether the shower is real, and learn about its origin. This is important because it teaches us about a large, Earth-crossing comet which we haven't discovered yet.
Observers in North and South America are best placed to observe the event. Green and yellow areas in the map below indicate parts of the world where the sky will be dark, and the radiant above the horizon, near the predicted time of the meteor shower.