Leonids meteor shower peaks on the night of November 17/18, 2015

The Leonids is a famous meteor shower that's peaks this year on the night of November 17th / 18th. Up to 15 meteors per hour expected. What adds to the mystique of this shower is its fantastic history. Over the years the Leonids has produced some of the most spectacular storms ever seen with one famous outburst in 1833 being of incredible proportions. Even though no super storm is predicted this year, it's still a wonderful event on the celestial calendar.

Parent comet and great storms

The source of the Leonids is comet 55P/Tempel-Tuttle or as it's more commonly known Temple-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, Temple-Tuttle can pass close to the Earth and when this occurs chances of a witnessing a super storm are greatly increased.

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 1833 storm 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 the storms were now a thing of the past. There was no luck either 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 as many thousands of meteors were seen across North America. 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.

Leonids 2015

But what can we expect in the years between storms, like this year. Although we won't see anything like a super storm the good news is the waning crescent Moon won't significantly interfere. In most years the meteor shower produces a maximum zenithal hourly rate (ZHR) of 15 meteors per hour. This year's event will probably be no different.

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

The best time to look for the Leonids is after midnight on the night of November 17/18. The radiant is located about 20 degrees northeast of brilliant Jupiter and about 10 degrees north of first magnitude star Regulus. At magnitude -1.9, Jupiter is unmistakable. A few hours before sunrise Mars (mag. +1.6) and brilliant Venus (mag. -4.3) rise above the eastern horizon.

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 and 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'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) and appear to streak across the sky. Although the predicted ZHR is low you never know when you may witness a sudden brief burst of activity. Certainly, well worth looking!

Comet 55P/Tempel-Tuttle Data Table

Comet name 55P/Tempel-Tuttle Discoverer Ernst Tempel and Horace Parnell Tuttle Discovery date December 19, 1865 Aphelion (AU) 19.6924 Perihelion (AU) 0.9766 Semi-major axis (AU) 10.3345 Eccentricity 0.9055 Orbital period (years) 33.2226 Inclination (degrees) 162.486 Last perihelion February 28, 1998 Next perihelion May 20, 2031

Leonids Data Table