Report on the Leonid Meteor Storm of 2001
by Fred Espenak (Ayers Rock, AUSTRALIA)
Historical records extending back one thosand years show evidence of a semi-periodic meteor storm in Leo every 33-34 years. I lead a group of 16 people to Ayers Rock (Uluru), Australia for the express purpose of observing the predicted and much anticipated 2001 Leonid Meteor Storm. Our Spears Travel tour arrived in central Australia on November 16. After spending three days visiting the remarkable red monolith known to the aboriginal people as Uluru, we prepared for the big celestial event.
We assembled in the lobby of the Desert Garden hotel and departed for dark sky at 12:30 am on Nov. 19. During the previous two days, I had scouted the area for a suitable observing site with the able assistance of our bus driver John Smith. John and I settled on a location just eight kilometers from our hotel. About half a kilometer down a dirt road off the main highway, our isolated site offered dark skies and a commanding view in all directions.
The bus arrived at our site at 12:45 am and the group eagerly exited the vehicle. Everyone quickly staked a claim and set up their ground tarps, chairs and tripods. Pat Totten and Bob Shambora helped me carry my telescope and equipment a suitable distance down the dirt track where I could photograph the sky without interference.
Shortly after 1:00 am, I was busy assembling my equatorial mount when I heard the group roar as they greeted the first major Leonid meteor. Half expecting the spectacle to be over by the time I looked up, I was startled to see a relatively slow, bright meteor climbing up the eastern sky. It crossed high near the zenith and continued on its way to within twenty degrees of the southwestern horizon before burning out. Such an unusually long path (3/4 or more of the sky) is characteristic of a meteor grazing through the Earth's upper atmosphere. This is just what you would expect as the shower radiant rises about the northeastern horizon.
As I continued to erect and align my telescope, the cool night air was punctuated by 'Oh!', 'Ah!' and an occasional 'Wow!' with increasing frequency. After an optical polar axis alignment on Sigma Octanis (the southern pole star), I was finally ready to begin photography around 2:30 am. I was shooting simultaneously with four cameras using lenses with focal lengths of 16mm, 24mm, 28mm and 35mm. During my ten minute exposures, I was free to lie on my ground tarp and watch the incredible show above.
Over the course of the next half hour, more and more Leonids flashed across the sky. Although I didn't have the time to make meteor counts, it was clear that the rates were dramatically increasing. By 3:00 am (17:30 UT), I was typically seeing ten or more meteors per minute. The distribution was quite patchy with two or three meteors often appearing within several seconds of each other followed by gaps sometimes lasting tens of seconds.
One especially notable Leonid was as bright as the full moon as it flashed through Taurus. It left an unbelievably luminous trail that persisted as a narrow filament a minute later. As upper atmospheric winds acted on the trail, it slowly dispersed and drifted to the Southeast. Fifteen minutes after the bolide, the trail was still visible as a broad diffuse ribbon in western Orion.
Another bolide lit up the southern sky near the Large Magellanic Cloud (see photo above). Once again, a bright trail was seen which persisted for more than ten minutes as it slowly drifted south. I saw one fireball indirectly when it lit up my observing site while I was looking down at my telescope. I caught a final glimpse of it as it quickly disintegrated.
I was particularly surprised to note many meteors were seen at low elevations in the range of ten to twenty degrees. I believe this to be a selection affect which arises because the low view angles pass through longer paths through Earth's atmosphere resulting in a greater chance of seeing a meteor.
Around 3:30 am, I noticed a remarkable phenomenon. Looking to the southwest, I saw four Leonids all within two seconds. But what really grabbed my attention were the trajectories of these meteors. Everyone knows that meteor showers appear to radiate from a fixed* direction among the stars called the shower radiant. For the Leonids, the radiant is in the constellation Leo (near gamma Leo). All shower members appear to DIVERGE from the radiant. So if you trace a meteor's path backwards, it will lead you back to Leo.
But the four meteors I saw were in the opposite direction from Leo, and they were all CONVERGING toward a point below the southwestern horizon. It was at that instant that I realized I was seeing the 'anti-radiant' of the shower! I must confess that I'd never heard of such a thing but it was clearly obvious as I watched other meteors in that direction.
By 4:15 am, the zodiacal light was growing quite bright in the east. We continued to watch the abundant meteors with a growing sense of sadness since morning twilight would soon end the show. I completed my photography program at about 4:40 am and I stretched out on my ground tarp to enjoy more meteors in the slowly increasing twilight. At 5:15 am, I finished packing up my equipment and headed back to the bus. Although it was half an hour before sunrise, I could still catch the occasional flash of a really bright Leonid!
* The shower radiant actually shifts slowly due to Earth's orbital motion.
All photographs are copyright by Fred Espenak.
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Last revised: 2003 Dec 27