Rich in history, the Leonid meteor shower returns this month to light the frosty nights.
Like an old friend enticing you on a new adventure, the annual Leonid meteor shower returns this month with promises of fiery comet shards dashing across the night sky. Conditions are nearly ideal for viewing. The shower peaks between midnight and dawn on Monday and Tuesday mornings, November 17th and 18th. No worries about moonlight this time around — the demure lunar crescent won’t rise until 2 or 3 a.m.
Leonid meteors hail from periodic Comet 55P/Tempel-Tuttle, which circles the Sun once every 33 years. Comets make the best meteor shower parents because they give till it hurts. Every time 55P/Tempel-Tuttle swings through the inner solar system, its dust-laden ices vaporize under the heat of the Sun, releasing gases and debris along its orbit.
Round and round the comet goes, spawning multiple ribbons of dust. When Earth’s orbit intersects the comet’s path, we slam into a tenuous interplanetary dust storm. Sand and gravel-sized bits strike the atmosphere 60 to 70 miles (100 to 115 km) overhead and vaporize in a fury of light called meteors — o,r as many refer to them, shooting stars.
In most years, you can see 10 to 15 Leonids per hour emanating from a point in the sky called the radiant in the Sickle of Leo the Lion, an asterism shaped like a reverse question mark; it's not far from the bright planet Jupiter this fall. Leonids will shoot all over the sky, but if you trace them backward, they'll all point back to the radiant, the point in the sky toward which Earth is traveling as we meet Tempel-Tuttle's dusty debris head on.
Every 33 years, Tempel-Tuttle makes a pass through the inner solar system, and we witness a greatly enhanced shower, called a meteor storm, if counts exceed 1,000 per hour. During the remarkable storm of 1833, a thousand meteors per minute were reported by alarmed townsfolk. Ever since, astronomers have been on the lookout for increased activity every 33 years, and the Leonids have generally obliged.
During the November 17, 1966, shower, observers in the western United States witnessed the greatest show of modern times. In the hour before dawn, 144,000 Leonids per hour briefly streaked across the sky like a soundless 4th of July fireworks finale.
This was the first meteor shower I ever attempted to see, but clouds plastered the sky that morning above my Illinois home. I stood at the window in feet pajamas waiting in vain for a clearing. Years later, my luck would change.
By the early 1970s, the Leonids had tamped down to their usual dozen an hour. Not until 1998 did the shower’s pulse quicken again. Cresting to another extended peak from 1999 to 2002, the well-publicized displays bedazzled millions across the planet. Luminous meteors, exploding fireballs, and long-lasting trains removed the sting of that starless sky of 1966.
Besides their fireballs, the Leonids are famed for their trains, the name given to the glowing trails of hot, ionized atmospheric gases left behind by flaring meteors. Some last for minutes as they twist and expand, blown about by high-altitude winds. While nearly all showers feature meteor trains, the Leonids have the lion’s share, if you’ll pardon the pun.
Because the Leonid stream travels around the Sun in a direction opposite to the planets, Earth hits Tempel-Tuttle's debris head-on at very high speed. Leonids pepper our planet at speeds upwards of 158,000 miles per hour (70 km/sec), the fastest of any shower. Trains left by incandescent dust can linger many minutes, taking on a life of their own. Keep an eye out for them during the upcoming shower. A pair of binoculars will extend your viewing time of this unique phenomenon.
All that said, watching an “off year” Leonid shower takes fortitude. November nights can be shivery cold. Chills can be avoided by dressing in several layers of warm clothing, felt-lined winter boots, and insulated cap, not to mention making sure you have something hot to drink at hand. I find that the common reclining lawn chair makes an ideal meteor observing station. Since meteors can appear anywhere in the sky, what direction to face isn't critical, but anywhere in the general direction of Leo will be fine, east or south. Tuck yourself under a warm blanket and simply look up. What could be easier?
If you're really enterprising, that Moon we talked about earlier could be fertile ground for seeking lunar Leonids through the telescope. With about 75% of its surface in darkness, you might just spy the contrasting flash of an impacting meteoroid. You can observe visually with a 6-inch or larger telescope, or even better, hook up a video camera to your scope and record it for viewing later.
While a dozen meteors an hour isn’t many, you might be rewarded with a fireball or an exceptional train. You’ll also be honing your meteor-watching skills, which you’ll put to good use again during the richer Geminid meteor shower that peaks on December 14th. I look at it this way: if the sky’s clear, go for it. You never know when clouds might ruin the next big, hoped-for event. Experience teaches that if you keep your expectations modest, even a single meteor can be a joy.
Looking at the Moon? Let Sky & Telescope give you a hand with our laminated Moon Map!