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The Leonids is a famous prolific meteor shower associated with comet 55P/Tempel–Tuttle. It is active during the month of November with peak activity occurring on the night of the 16/17th November 2012. Much of the hype surrounding the Leonids derives from its history; it has produced some of the most spectacular meteor storms ever seen. One particular outburst in 1833 was of incredible proportions.

The comet that is the source of the Leonids is 55P/Tempel–Tuttle or more commonly known just as Temple-Tuttle. It is a periodic comet that was discovered by Ernst Tempel on December 19, 1865 and then independently by Horace Parnell Tuttle on January 6, 1866. With an orbital period of only 33 years, it can pass close to the Earth. On such occasions, the chances of a witnessing a super meteor storm are high indeed.

Comet 55P/Tempel–Tuttle (H. Fukushima, T. Nakamura, T. Sekiguchi / National Astronomical Observatory, Japan)

Great Storms

The first reported Leonid storm was made in 902 AD by Chinese astronomers and observers in Egypt and Italy. Many more spectacular Leonid storms followed, but one, the superlative storm of 1833 cemented itself in folklore. This storm was a phenomenal sight, witnessed by many and visible over the entire region of North America east of the Rocky Mountains. At the peak it was estimated that up to 200,000 meteors per hour rained down from the heavens. Not only was the storm a spectacular sight, but it also helped to significantly develop the scientific study of meteors. Previously meteors had been thought to be atmospheric phenomena, but the 1833 great storm helped change ideas.

The Leonids meteor storm returned in 1866 with reduced rates, but still of the order of thousands per hour. Unlike in 1833, this time the storm was visible over Europe and the sheer number of meteors startled observers, who scrambled to count them and determine the radiant position. An orbit was calculated for the meteors of 33 years, which tied in exactly with the recently discovered comet Tempel–Tuttle.

There was great anticipation for the return of the meteors in 1899, but to massive disappointment the storm failed to materialise. It was widely believed that the dust had moved on and storms were now a thing of the past. There was no luck either in 1933, but this may have been more down to bad weather rather than lack of a storm. After two disappointing cycles, the Leonid meteor storm returned with vengeance in 1966, as many thousands of meteors were seen across the North American sky. A spectacular display also occurred in 1999. Although not as prolific as that of 1966, hundreds to thousands of Leonid meteors per hour were still visible.

Great Leonid storm of 1966 (A. Scott Murrell)

Leonids 2012

But what can we expect in the years between storms, like 2012?

We won't see anything like a super storm. In most years the meteor shower produces a maximum zenithal hourly rate (ZHR) of only 10-15 meteors per hour. This year will probably be no exception.

Observing

The best time to look for the Leonids is after midnight on the morning of November 17. The radiant is located about 10 degrees north of first magnitude star Regulus in Leo.

Leonids Radiant and Star Chart

Leonids Radiant and Star Chart - pdf format

Once you have located the radiant, scan the general surrounding area of sky, preferable while sitting or lying down on a deck chair or something similar. Like all periodic showers, the meteors can appear many degrees away from the actual radiant, even in a completely different area of the sky. For each meteor noted, trace it back and if it originates from the Leonid radiant, then it is a true Leonid.

The Leonid meteors themselves can be quite bright, travel relatively fast at 70km/sec (157,500 km/hour or 98,000 miles/hour) and appear to streak across the sky. This year is a great time to look, as the waxing crescent moon will not interfere. Although the predicted ZHR is low, you never know you may witness a sudden brief burst of activity. Certainly, well worth looking!

Comet 55P/Tempel-Tuttle Data Table

Comet name55P/Tempel–Tuttle
DiscovererErnst Tempel and Horace Parnell Tuttle
Discovery dateDecember 19, 1865
Aphelion (AU)19.6924
Perihelion (AU)0.9766
Semi-major axis (AU)10.3345
Eccentricity0.9055
Orbital period (years)33.2226
Inclination (degrees)162.486
Last perihelionFebruary 28, 1998
Next perihelionMay 20, 2031

Leonids Data Table

Meteor shower nameLeonids
Radiant constellationLeo
Parent comet55P/Tempel–Tuttle
DatesNovember 6 -> November 30
Peak dateNovember 17
RA (J2000)10h 08m
DEC (J2000)+22d
Speed (km/s)70
ZHR15 (var)