 |
 |
 |
 |
 |
 |
 |
 |
Introduction
The reason why Leonids (LEO) deserve such a special place both on our homepage and in this year’s school of astronomy is the spectacular meteor storm expected to occur on November 17th this year. Every 33 years Earth crosses the main filament of Leonid meteoroid stream. Our preparation consists of introducing new members into basic techniques of visual observation and data reduction, while the more experienced members will test VLF technique of observation along with video camera testing.
Summary
Radiant position: a = 153:2 d = 22:0
Radiant drift: Da = 0:70 Dd = -0:42
Period of visibility: November 14th - November 21th
Maximum: lo = 235:15 (November 18th)
ZHRmax = up to storm r = 2.5
Hb = 128 km He = 87 km
Parent body: 55P/Tempel-Tuttle
Visibility
The Leonids are beyond doubt the most spectacular meteor shower observed in last 200 years. In contrast with some other periodic showers the Leonids have already formed a closed loop of material around their orbit, ahead and behind the original bulk of particlesreleased from their parent comet. This enables us to observe moderate rates on an annual basis. The years preceding and following the perihelion passage of the parent body produce very high ZHR.
Predictions for 1998 - 1999
In 1998:
Time of peak: 18 - 23 h Universal Time (UT), most likely around 19.7h UT = 11.7 h PST = 2.7h Bangkok, Thailand.
Expected meteor rates: 2000-10,000 meteors/hr per visual observer (peak at early morning hour: radiant in the zenith). Possible peak range: 100 (no storm) - 20,000
Dust density outside atmosphere: 10E-23 g/cm3.
Duration of the shower: 2x 1/e duration = 0.7 hours, total about 1.5 hours.
Activity curve: exponential increase and decrease of rates with time.
Magnitude distribution index: 3.0±0.2 (numbers increase by factor 3 every magnitude)
Best observing locations: 21±40 degree North, 120±45 degree East, best over China, Japan?, Phillipines, Vietnam and Thailand
Radiant high enough above the local horizon at Latitute +15N: 01-06 hours local time
Hours of dark sky: until beginning of astronomical twilight
Moon: new Moon
In 1999:
Time of peak: 0-5 h Universal Time (UT), most likely around 1.7h UT
Expected meteor rates: 2000-10,000 meteors/hr per visual observer (peak at early morning hour: radiant in the zenith). Possible peak range: 100 (no storm) - 100,000
Dust density outside atmosphere: 10-23 g/cm3.
Duration of the shower: 2x 1/e duration = 0.7 hours, total about 1.5 hours.
Activity curve: exponential increase and decrease of rates with time.
Magnitude distribution index: 3.0±0.2 (numbers increase by factor 3 every magnitude)
Best observing locations: 21±40 degree North, 30±45 degree East, best over Europe and northern Africa
Radiant high enough above the local horizon at Latitute +20N: 01-06 hours local time
Hours of dark sky: until beginning of astronomical twilight
Moon: 10 days old, will set during night
Satellites to be "Sandblasted" by Leonid Storm
Dr. William H. "Bill" Ailor of The Aerospace Corporation told a congressional subcommittee in Washington May 21 that the estimated 500 satellites on orbit "will be sandblasted" by the Leonid meteoroid storm due November 17.
But he said the effects on spacecraft are expected to be minimal, despite the fact the storm "will be the largest such threat ever experienced by our critical orbiting satellite constellations."
Ailor, director of the Center for Orbital and Reentry Debris Studies established last year at The Aerospace Corporation, presented his testimony during a hearing titled ‘Asteroids: Perils and Opportunities’. He was invited to appear before the Subcommittee on Space and Aeronautics, a panel of the House Committee on Science, by U.S. Rep. Dana Rohrabacher (R-Calif.), subcommittee chair.
‘It is possible’, Ailor told the subcommittee, ‘that some satellites will be damaged, but the most likely source of damage will not be from a rock blasting a hole in a satellite, but rather, from the creation of a plasma, or free electric charge on the spacecraft. The charge could cause damage to
computers and other sensitive electronic circuits on board the spacecraft, and ultimately cause the spacecraft to fail. For example’, Ailor said, ‘during the 1993 Perseid meteor shower, it was determined that the Olympus communications satellite was damaged by a meteor strike and went off the air shortly thereafter as a result of an electrical failure.’
Ailor also pointed out that the latest information on the coming Leonid meteoroid storm was presented at the Leonid Meteoroid Storm and Satellite Threat Conference sponsored by Aerospace and the American Institute of Aeronautics and Astronautics in Manhattan Beach, California, on April 27 and 28.
‘The primary recommendations from the conference’, Ailor reported, ‘were that, while it is very unlikely that the storm will have any major effect on satellites, the 'A-team' of controllers should be on duty during the meteor storm, and operators should check the state of health of their satellites frequently, looking primarily for electrical anomalies and glitches. It was also recommended that, if possible, satellites be oriented so that sensitive components are shielded from the oncoming stream of particles, and that recovery plans be in place should there be a spacecraft system failure during the storm.’
Ailor said that Aerospace collected information on spacecraft anomalies experienced during the 1997 Leonid shower and will be collecting similar information for the 1998 and 1999 events. "This information will help us plan for the 1999 Leonid and future meteoroid storms. It may also help us to understand whether additional safeguards against the meteoroid impact threat should be included in future spacecraft designs", Ailor said.
Ailor's full testimony is on the Internet at http://www.aero.org/leonid/.