Johannesburg Centre, Astronomical Society of Southern Africa


Two of the best Meteor Showers coming up.

On November 14th to 17th, the Leonid meteor shower should be visible. It is predicted that either this year or next year there will be an exceptionally prolific shower, so it may well be worth watching out for it. The hourly rate may reach 20,000 meteors!! The night of the 16th/17th is when the greatest activity should happen.

Also coming up is the Geminids in December. The peak is predicted on the 14th but for the keen observer it will be worth watching a day or two before and after the predicted maximum.

Leonid fireballs galore! Nov 15/16

George Zay
Descanso, California

Meteor/Leonid observations for the night of Nov 15/16, 1998 from Descanso, California, San Diego County.

I just got back from the best meteor shower I've ever witnessed. I observed from my Descanso, calif. observatory under clear skies with Bob Lunsford. I have a teff of about 7.5 hours and an LM near 6.0 for most of the night.

I plotted until about midnight and then just record data without plotting.

I recorded a total of 140 meteors. 77 were Leonids, 31 N. Taurids, 2 S. Taurids and 30 Sporadics. But!! out of the 77 Leonids I recorded 25 fireballs.

I also recorded a brilliant N. Taurid fireball with a magnitude of -12. I thought that was gonna be the highlight of the night...but it didn't even come close.

The magnitudes of the Leonid fireballs are as follows:-3,-3,-3,-3,-3, -4,-4,-4,-4, -5,-5,-5, -6,-6,-6,-6, -7,-7,-7, -8,-8,-10, -12,-12, -15

The trains lasted quite long for a lot of them. One -7 had a train last 30 seconds, then the other two -7's had trains lasting over 100 seconds each, one of the -8's train lasted over 100 seconds as well. The -10 had a train last 4.5 minutes and the -15 train lasted over 8 minutes. The -15 and a -12 had persistent trains that were of magnitudes of around -8 for a few seconds it seemed. They snaked and twisted all over the place. It was hard to keep count of their durations because often another fireball would show up. The -15 occurred above and behind us...the stars totally disappeared and the sky looked like daylight blue for a second or two. It was pure old excitement. I wanted to go to the bathroom, but didn't dare because I was afraid I would miss another fireball.

The strange thing about last nights activity, there were very little dim meteors...that is those that were of around +3 or dimmer. Besides the fireballs, I also recorded three that had magnitudes of -2 and 8 were of –1 magnitudes. I won't have time to do my report for a few days...but I bet my mean magnitude will be around -3 or more? Never had this happen before. We were caught completely off guard for this kind of activity the night before the leonid maximum. I hope to be out there again tonight for the Leonid maximum...if the weather holds out? Now to get some shut eye...I might have to do a road trip to an area in the desert near Yuma, Arizona if that front comes down like it might...got my toes crossed.

Satellites May Be Shattered By Invisible Meteors

Author: Robert Matthews

New Scientist issue 3rd October 1998

THE Leonid meteor storm that may light up the sky in Asia when it strikes the Earth next month (Nov) could pose a bigger threat to satellites than astronomers had feared.

Every year, around mid-November, the Earth crosses the orbit of a comet called Tempel-Tuttle and passes through debris the comet has shed. This burns up in the upper atmosphere as a meteor shower. Every 32 to 33 years, the Earth runs into an especially dense cloud of debris, turning the shower into a storm. At the peak of the last storm, in 1966, the skies above North America were lit up by 5000 meteors in just 20 minutes.

Astronomers are now bracing themselves for the next Leonid storm, predicted to reach a peak around 17 November. Communications and other satellites could be threatened by the bombardment - and both NASA and the Russian Space Agency have postponed launches until the danger has passed.

No one knows just how bad the damage will be. For example, astronomers can't predict with certainty exactly where the densest part of the debris cloud is. Now Duncan Steel, an astronomer with Spaceguard Australia in Adelaide, has thrown another variable into the equation. If his model of the chemical composition of the Leonid meteors is correct, attempts to observe the approaching meteors may detect only a few per cent of them.

Steel says that data gathered during the recent visits by comets Hale-Bopp and Hyakutake reveal that the dust these comets gave off was rich in volatile organic compounds. If the same is true of the cometary debris that forms the Leonids, most of the meteors may be invisible. This is because if they are made of highly volatile material, many will burn up at relatively low temperatures - too low to leave behind glowing trails detectable from the ground. Cool-burning meteors will also emit relatively few electrons, and that will make them invisible to ground-based radars, which can only spot electron-dense trails.

"If small meteoroids in storms are largely composed of organics, then none of the data collected to date gives a realistic assessment of the hazard level," says Steel, whose conclusions are published this week in the journal

Astronomy and Geophysics (vol 39, p 24).

Current estimates put the risk of a serious impact between a meteor and a large satellite at about one in a thousand. Steel says his study suggests that this "seriously underestimates" the hazard. "If I am right, the economic loss caused by the Leonids may be immense," he says.

Other astronomers agree that the reliability of the storm predictions depends crucially on the composition of the meteors. "Steel's paper is very interesting - though whether it is actually correct is another matter," says Iwan Williams of Queen Mary and Westfield College, London. "We may know after the Leonids next month."

Steel's advice is not to rely too heavily on satellite communication and navigation systems in the coming month. "I would not depend for my life on the Global Positioning System being fully functional on 18 November," he says.


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