2007 was a special year for cometary scientists, offering an opportunity to study a rare class of comets as never before.
The so-called long-period comets enter the inner solar system fresh out of the Oort cloud and do not return until thousands of years later. For this reason, they are unpredictable and so difficult to study from the Earth and virtually impossible to visit by spacecraft.
The same cannot be said, however, for the trail of debris they leave behind. This material, appearing as meteors in the Earth's atmosphere can be investigated in depth provided a reliable prediction for a long-period-comet related meteor outpurst is at hand.
Adaptive Optics laser firing out of 3-metre dome
That was the case for comet C/1911 N1 Kiess and its associated meteor stream, the alpha Aurigids. This activity of this stream is typically very low, only a few meteors per hour, but on certain years of the 20th century, significant outbursts of ~100 meteors per hour were observed. These are now understood by a model of the dynamical evolution of the stream over time. The same model predicted a similar outburst at midday of 1st September, 2007. An observational campaign, officially known as the Aurigid Multi-Instrument Airborne Campaign or MAC, was put together to study this rare event. Video, digital and CCD cameras and spectrometers were fielded to collect as much information on these meteoroids at the point of their fiery demise in the Earth's atmosphere.
The Armagh Observatory made an early commitment to contribute to the ground support element of the Aurigid MAC by sending a group of three equipped with low-light level cameras and meteor-detection software to the US state of California, one of the few places where the predicted outburst would occur during nighttime with the radiant of the shower above the horizon.
To make maximum use of the available resources, we decided to deploy at two different sites in an effort to triangulate the meteor trajectories in three dimensions. That would provide orbital information on the meteoroids and enable a useful comparison with the orbit of the comet itself. Reasearch Astronomer Dr Apostolos Christou set up a camera within the grounds of Lick Observatory whereas PhD student Prakash Atreya and systems support officer Martin Murphy set up 70 km further south, at Fremont Peak.
Meteor camera at Fremont Peak Observatory
Accompaning Dr Christou was Bryan Murahashi of Lockheed Martin while at Fremont Peak we were joined by a group of meteor astronomers led by Daniel Fischer of the German meteor working group.
The weather was fortunately clear at both sites despite an earlier concern about fog out of the SF bay area. We set up and waited. At around 03:30am local time the first Aurigids began to appear indicating that the prediction was to be borne out. The rate picked up over the next hour or so peaking at around 04:15am, interestingly a quarter of an hour earlier than the predicted maximum, and at a level of about 100/hr, similar to that of the Perseids albeit for only 10-15 min.
Visually, the meteors were yellowish in colour leaving short-lived trains with two or three occuring simultaneously. Despite the bright moon several tens of Aurigids were captured by the cameras, some of them significantly brighter than the brightest stars in the sky. Ironically, the observations by Dr Christou were carried out at the same Observatory from which Carl Clarence Kiess discovered the parent comet of the Aurigids that now bears his name.
Animation of Aurigid detections from Lick Observatory site.
The very bright object is the Moon.
Animation of Aurigid detections from Fremont Peak Observatory site.
The bright star is Capella.
Bright fireball close to the moon
See also: Aurigid MAC - Peter Jenniskens
Report from Daniel Fischer
Photographs from Bryan Murahashi
2007 Alpha-Aurigids - Jeremie Vaubaillon
The Aurigid Project for amateur observors
Automatic Meteor Detection System
Last Revised: 2009 November 5th