Look out for the Leonids!

The Leonid storm of 2001 was memorable. Two fireballs were captured during the shower. Image: Tony Hallas.

The Leonids, one of the most famous of all meteor showers, is predicted to reach its peak of activity this year at around 06:00 UT on the morning of 18 November. Observed rates seen under good conditions and dark skies should be in the region of just 10 to 15 an hour. Leonids are among the swiftest of meteors, smashing through the upper atmosphere at around 71 kilometres per second, and are often bright and leave persistent trains or trails across the sky. Thankfully, the Moon, a waxing crescent, sets at 7pm and won’t spoil the show.

The Leonid meteor shower peaks at about 06:00 UT on the morning of 18 November. The shower’s radiant lies in Leo’s famous ‘Sickle’ asterism. AN graphic by Greg Smye-Rumsby.

Meteors are tiny particles of material (called meteoroids when out in space) that plunge into Earth’s upper atmosphere, their ionised atoms giving rise to the streaks of light that we see. Meteor showers occur at particular times of the year when Earth encounters the orbital stream of this material left over from periodic comets. The Leonids parent comet is 55P/Tempel-Tuttle, which returns to the inner Solar System every 33 years. As the Sun warms its surface icy surface it releases gases and dust, replenishing the Leonid’s supply of material.

The Leonids have been producing only modest rates of shooting stars in recent years, but the shower is responsible for spectacular, landmark observing events of the past linked to the the return of comet is 55P/Tempel–Tuttle. In 1833, it’s thought an incredible 100,000 meteors per hour were experienced. For a few years centred around the time of the comet’s following return, between 1866 (most famously) and 1868, yearly storms were experienced. The storms of 1966, 1999, 2001 (the later two storms associated with 55P/Tempel-Tuttle’s last perihelion passage of February 1998) are the most spectacular storms in living memory. The comet’s next return will occur in May 2031, with rates expected to pick up from 2027.

A Leonid fireball. Image: NASA.

Meteors from a shower appear to emanate from a point in the sky called the radiant and each meteor shower has its own unique radiant and is named for the constellation where its radiant is situated; the Leonids radiant lies in Leo, hence their name. 

The Leonid radiant lies in Leo’s famous backwards question mark or ‘Sickle’ asterism, which is well clear of the eastern horizon by 1am.

A depiction of the 1833 Leonid storm. This engraving by Adolf Vollmy is based on a painting by Swiss artist Karl Jauslin.