★ Leonid Meteor Shower

The Leonids are the meteor shower with the most dramatic past. In most years they are a modest show, with about 15 meteors an hour at best under a dark sky. But at intervals of roughly 33 years, around the time their parent comet returns, they have produced meteor storms. Even in an ordinary year they are worth getting up for: Leonids are among the fastest meteors you can see.

Where the meteors come from

The Leonids are dust from Comet 55P/Tempel-Tuttle, a small comet with a nucleus about 3.6 km across that goes around the Sun every 33 years. It last passed closest to the Sun in 1998. On each pass it sheds a narrow trail of dust, and forecasters name these trails after the year the comet released them. In most years Earth meets only older, spread-out material. Now and then the planets' gravity steers a denser trail into Earth's path, and rates jump sharply for a short time, most often in the years around the comet's return. The grains hit the atmosphere at about 71 km/s.

When to watch

The Leonids are active from November 6 to 30, and the peak usually falls on November 17 or 18. The table above gives the expected peak time and the Moon. From mid-northern latitudes the radiant rises in the east-northeast around 11 p.m. to midnight, and rates climb as Leo gets higher, so the last two hours before dawn are best. Soon after the radiant rises, look for earthgrazers: meteors that skim close to the horizon, known for long, colorful tails. Predicted dust-trail encounters are noted under the table.

How to find the radiant

The radiant is in the Sickle of Leo, a backward question mark of stars that forms the Lion's head, with bright Regulus as the dot at the bottom. The radiant sits inside the curl of the Sickle, about 10° (a fist at arm's length) north of Regulus, close to the star Algieba. By dawn it stands high in the southeast. From the Southern Hemisphere, Leo rises later and stays lower in the north, so rates are lower.

What to expect

In an ordinary year the ZHR is about 15. With Leo around 60° high before dawn, a dark rural site might give you around 10 an hour on the peak morning; from the suburbs, expect three to five. At 71 km/s these meteors are gone in a fraction of a second. A population index of 2.5 means a fair share of bright ones, and Leonids can be colorful. Many bright Leonids leave a train, a glowing streak that hangs in the sky after the meteor has gone. Storm rates, at least 1,000 meteors an hour, are rare.

Viewing tips

• Set an alarm for 2 or 3 a.m. instead of staying up all evening.
• Dress for winter; a sleeping bag on a reclining chair helps.
• Lie with your feet toward the east and take in as much sky as you can.
• If the Moon is up, keep it behind you or hide it behind a building.
• For photos, aim a wide-angle lens about 45° from Leo; a bright Leonid's train may show in the next frame.

History and notable displays

The Leonids produced meteor storms in 1833, 1866, 1966, 1999, 2001 and 2002. The storm of November 13, 1833 was seen across eastern North America. Denison Olmsted of Yale gathered reports from the whole eastern half of the continent and noted that the meteors radiated from a point in Leo that moved with the stars, which suggested they came from space. After studying old records, Hubert Anson Newton predicted another storm for 1866, and strong displays followed over Europe and the United States from 1866 to 1868. The parent comet was found independently by Ernst Tempel in 1865 and Horace Tuttle in 1866. In 1966, observers saw meteors at rates of thousands a minute for about 15 minutes.

The comet is next due closest to the Sun on May 20, 2031. The American Meteor Society expects good displays, with rates over 100 an hour, around its returns in 2031 and 2064, but probably no storms before 2099.