Camelopardalids… more like the Camelopardaliduds or the Camelordalididn’ts.
Last weekend’s much anticipated Camelopardalid meteor shower from comet 209P/LINEAR was a big disappointment for most meteor watchers. Rather than ZHRs of 100-400, the peak ZHR only reached ~15 per hour. Making things even worse, the ZHR rate is not the rate of actual visible meteors (ZHR is meant for comparing different showers under different observing conditions; ZHR is an idealized rate only valid for observers under very dark skies and with the radiant overhead). Still a Camelopardalid ZHR of 100-400 should have produced 15-60 meteors per hour for the average observer. The actual ZHR of 15 means that most people saw a couple of Camelopardalids per hour at most.
Before going into what went wrong, let’s look at what we got right.
Comet 209P/LINEAR does produce meteors and, in particular, laid down a number of dust trails that caused a meteor outburst. In fact, the predicted time of for crossing the dust trails appears to have been spot on.
What went wrong? Obviously our understanding of the properties of the dust of 209P and perhaps even their exact location in space was wrong. The dust the Earth encountered was smaller than expected. Combine that with slow encounter velocities (19 km/s) and you get a shower that produced meteors that were too faint to be seen visually. Meteor radar observatories such as the Canadian Meteor Orbit Radar and the Japanese Radio Meteor Observatory saw many more meteors in the 6th to 7th magnitude range.
In short, the biggest problem was that we were going into this shower blind. For a few years around 2000, very accurate predictions of the Leonids were made. But these predictions had the benefit of centuries of positive (and negative) observations to better quantify the number of meteors that could be seen. The Camelopardalids had no ‘back catalog’ of meteor outbursts. Not only were no outbursts observed prior to this year but the parent comet was only discovered in 2004. So we had no knowledge of how active, or even if the comet was active at all, prior to discovery.
For the people who study meteor showers and their parent comets, the shower (dud or not) was a learning experience and the data we collected is still very useful. 209P is making a very close approach to Earth (~0.06 AU tonight) and it is almost unprecedented that we can observe such a low-activity comet this close.
For more analysis and some early results on the shower, check out the pages by Peter Jenniskens and Sky and Telescope.