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H i s t o r y

1833 Activity

The first apparition of the Leonids in modern times is the November 12-13, 1833 display. This display has been dubbed "the birth of modern meteor astronomy." On the morning of the 13th of November that year, the people of eastern North America were treated to a display when the sky was lit up by thousands of meteors during the 4 hours before dawn. The display was of a short duration and was not seen by people in Europe or other parts of the world.
This apparition was important because for the first time a reasonably accurate position was able to be calculated for the stream. This was more accurate than just a direction in the sky or a constellation that meteors were seen to radiate. The display also enabled astronomers to predict a 33 to 34 year period for the return of the Leonids, and it was predicted that the Leonids would return in 1866.

1866 to 1869 Activity

As a result of the 1833 display, Leonids apparitions for the past 2000 years were identified. The years 585, 902, 921, 934, 1002, 1202, 1366, 1582, 1602, and 1698 were identified as having Leonids storms by Hubert A. Newton. The expected return of the Leonids occurred on Nov 13-14 1866 with a display reaching 2000 to 5000 meteors per hour. There were lower rates in a display in 1867 of around 1000 per hour (this event was hampered by moonlight.) In 1868 there was another strong display of around 1000 per hour. There was a final strong display on Nov 14 1869 when rates reached around 200 per hour. In the years after this the rates went back to their usual levels of 10 to 15 meteors per hour. A great deal of knowledge was subsequently gained.

1899 to 1903 Activity

It was predicted that the Leonids would produce strong storm activity in 1899. These predictions were made public in newspapers in Europe and the USA. Although hourly rates of 50 to 100 per hour were seen in the United States there was no meteor storm. This storm failure was described by Charles P. Oliver as "the worst blow ever suffered by astronomy in the eyes of the public". However, hourly rates were calculated to be a maximum of 40. It was shown that the meteor stream had encounters with Jupiter in 1898 and Saturn in 1870 that caused a shift in the stream's position and consequently no storm developed.
The actual peak for this 33 year cycle came on Nov 14-15 1901 when rates of around 400 per hour were observed at Carton College in Minnesota. Moonlight caused the Leonids to be barely detected in 1902. There was however, a reappearance in 1903 when a maximum hourly rate of 200 surprised John R. Henry observing in Dublin. The Leonids returned to normal in the following years with rates ranging from 5 to 20.

1928 to 1939 Activity

The next apparition of a Leonid storm was predicted as being most likely in 1932. Enhanced activity was noticed in 1928 with hourly rates around 50 or more. During 1929 rates were lower, around 30 per hour but this was hampered by moonlight.
The Leonids showed some activity in 1930 with rates between 130 and 190 meteors per hour under moonlight as seen by observers in the United States. Rates in 1931 were only a little higher owing to no interference from the moon.
The year 1932 was looked on with some anticipation as rates had been steadily climbing and a storm had been predicted this year also. There was to be no storm. Maximum rates around 240 were observed by J. P. M. Prentice. Even after taking into account the moon's interference, it was clear there had been no "storm level" activity.
During the years between 1933 to 1939 Leonids rates declined slowly remaining around 30 to 40 per hour. The span of 12 years between 1928 and 1939, quite a long period, had produced enhanced Leonids rates.

1961 to 1969 Activity

During the 40's and 50's Leonids rates were their normal 15 to 20 per hour. During the period of 1947 to 1953, rates had declined to between 3 and 11 per hour causing the Leonids to be overlooked during the following years by many observers. As a result, the return to high rates in 1961 was missed by many. In that year, Dennis Milon and 5 other amateur astronomers observing out of Houston, Texas, observed hourly rates of between 50 and 60 on November 16.
The 1962 and 1963 displays went back to normal levels with rates between 15 and 20. 1964 produced rates up to around 30 per hour. Observers in Hawaii and Australia in 1965 were treated to the best display since 1932 with highest rates for that year at 120 per hour. An interesting item with the 1965 display was that from Woomera, Australia between Nov 16.65 and 16.77 UT observers reported 38 Leonids with an average magnitude of -3 indicating a high number of fireballs in this time! This increase in activity stirred some optimism in the astronomical community with the predicted maximum a year away.
On the night of November 17 1966, for observers in North America, this optimism was well rewarded. Meteor observer Dennis Milon and a dozen others observing from Arizona, USA were treated to a memorable night. Observers watching between 2.30 am and 6.40 am Local Time observed a peak Leonid rate of 40 meteors per second at 5.54 LT (November 17.50 UT). Activity declined after this but was still as high as 30 per minute an hour later!
These rates translate into a maximum of 2400 per minute of a whopping 144,000 Leonids per hour, a truly magnificent display. There was another report from observers at Table Mountain Observatory, USA of 50 per second or 180,000 per hour. This outburst lasted for about 10 minutes before declining. Observers in the eastern half of the USA reported lower rates, generally less than 200 per hour indicating that the peak of the storm was over a very short duration. Observers in other parts of the world observed similar rates.
Observers were treated to high rates in 1967, 1968 and 1969, with between 100 and 150 Leonids per hour seen before returning to normal in 1970. Rates remained at this level until the current cycle of increased activity.

1994 to 2000 Activity

Increased activity started in 1994. Both visual and radio observers detected above normal rates. The night of November 17-18 showed short outbursts with a ZHR (Zenithal Hourly Rate) of 70 to 80. The 1995 maximum proved to be quite broad and lasted over 24 hours with a maximum ZHR of 35. The 1996 apparition had a very similar ZHR of around 60 but with a notable difference: many fireballs were observed.
The 1997 display maximum was expected to occur over the North American west coast and across to Hawaii on November 17th. Strong moonlight resulted in difficulties in observing and resulted in a large range of ZHR's. The peak time was calculated to have occurred between 10.30 UT and 13.00 UT on the 17th. The calculated hourly rate was between 110 and 170. This was the best display so far of the 33 year cycle.
The highlight of the Leonid's return came in 1998. Although no major storm activity was observed, there was a period of high activity one day before the predicted peak. An outburst of brighter Leonids and fireballs was observed by those watching from Australia to Europe. The display lasted from Nov 16th 15.30 UT through to Nov 17 12.00 UT and produced an average ZHR of 260 at maximum. The display was fantastic with many bright fireballs and bolides as bright as 16 magnitude. The display was unpredicted. A second increase in activity was observed around 1 day later at the time of the predicted maximum, the ZHR of this increase in activity was an average of 100.

Acknowledgements

The above information was provided by Adam Marsh, Director Astronomical Society of Victoria Meteor Section, and the Astronomical Society of Frankston Meteor Group. For further information on predictions and observing hints see the International Meteor Organisation website