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The Leonids is a famous meteor shower that's peaks on the night of Friday, November 17, and early the following morning. What adds to the mystique of this shower is its fantastic history. Over the years it has produced some of the most spectacular storms ever seen, including a famous outburst of incredible proportions in 1833. Even though no super storm is predicted this year, the event is very favourable and promises to be a good one as the new Moon won't interfere.

Great Leonid storm of 1966 (credit:- A. Scott Murrell)

Parent comet and great storms

The source of the Leonids is comet 55P/Tempel-Tuttle, or as it's more commonly known Tempel-Tuttle. It was discovered by Ernst Tempel on December 19, 1865 and independently by Horace Parnell Tuttle on January 6, 1866. With an orbital period of 33 years, Tempel-Tuttle can pass close to the Earth and when this happens the chance of a witnessing a super storm is greatly increased.

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

The first Leonid spectacular was recorded by Chinese astronomers and observers in Egypt and Italy in 902 AD. Many more storms followed, but one, the superlative storm of 1833 cemented itself in folklore. It was a phenomenal sight, visible east of the North American Rocky Mountains with up to 200,000 meteors per hour raining down from the heavens. Not only was the storm a spectacular sight, it significantly helped develop the scientific study of meteors. Previously they had been believed to be atmospheric phenomena, but the great storm of 1833 helped change ideas.

In 1866 the storm returned with reduced rates, but still of the order of thousands per hour. Unlike 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. The calculated period of 33 years 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 that the previously observed great storms were now a thing of the past. There was also no luck in 1933, but this may have been more down to poor weather rather than lack of a storm. After two disappointing cycles, the Leonid meteor storm returned with vengeance in 1966 when many thousands of meteors were seen across North America. A spectacular display also occurred in 1999, and although not as prolific as that of 1966, hundreds of meteors per hour were still visible.

Leonids 2017

But what can we expect in the years between storms, like this year. Although it's extremely unlikely a storm will occur, up to 15 meteors per hour should still be visible. The best time to look is during the early hours of November 18th. The radiant is located about 10 degrees north of first magnitude star, Regulus (α Leo - mag. +1.4). Once you have located the radiant, scan the 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 from the actual radiant and often in a completely different region of the sky. For each meteor, trace it backwards and if it originates from the radiant then it's 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), appear to streak across the sky and often with persistent trains. Although the predicted ZHR is low and enhanced activity is unlikely until the late 2020s, you never know you may witness a sudden brief burst of activity. Certainly, well worth looking out for!

Leonids Radiant and Star Chart (credit:- freestarcharts)

Leonids Radiant and Star Chart - pdf format (credit:- freestarcharts)

Looking east a few hours before sunrise from northern latitudes on the morning of November 18, 2017 (credit:- freestarcharts/stellarium)

Leonids Data Table

Meteor shower nameLeonids
Radiant constellationLeo
Parent comet55P/Tempel-Tuttle
DatesNovember 6 -> November 30
Peak dateNovember 18
RA (J2000)10h 08m
DEC (J2000)+22d
Zenithal Hourly Rate (ZHR)15

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
Orbital period (years)33.2226
Inclination (degrees)162.486
Last perihelionFebruary 28, 1998
Next perihelionMay 20, 2031