Even mid-November the Earth (left, in blue) crosses the orbit of Comet 55P/Tempel-Tuttle. Debris left in its path strikes the atmosphere at high speed and burns up as meteors. (Peter Jenniskens and Ian Webster with additions by the author)
Bits of dust and small rock left by the comet in its orbit slam into the atmosphere as we plow headlong through the interplanetary blizzard. Heated to more than 3,000 degrees F, the fragments briefly shine white-hot and cause the air to glow around them as they barrel across the sky between 50 and 75 miles (80-120 km) over our heads. And yes, Leonids are fast! They zip by at 44 miles per second (158,400 miles an hour).
Depiction of the Great Leonid Storm on the night of Nov. 12-13, 1833. “At Boston, the frequency of meteors was estimated to be about half that of flakes of snow in an average snowstorm,” wrote Agnes Clerke, a Victorian astronomy writer. “Their numbers … were quite beyond counting.” (Public domain)
While modest, the Leonid shower is ever-reliable, producing 10-20 meteors per hour most years. This year’s peak occurs on Tuesday morning, Nov. 17. Every 33 years, around the time the comet cycles back toward the sun, we get much more spectacular shows with meteor counts in excess of 1,000 a minute. Only then does the Leonid meteor shower truly live up to its name. Meteor-watchers call them Leonid storms, and the last one occurred in 2001. After a couple of off-peak years, the next big storm is expected in 2099. Whoa, that’s a long time! To tide us over, we should see meteor counts in excess of 100 per hour when the comet returns again in 2031 and 2064.
Leonids appear to radiant from a point inside the asterism called the Sickle of Leo, shaped like a backwards question mark. This view shows the sky around 3 a.m. local time. (Stellarium)
Leo rises around midnight, but doesn’t really climb high enough for most shower members to clear the horizon until around 2 in the morning. That’s a fine time to watch, but you’re better off waiting until 4 and watching until the start of dawn around 5:30 a.m. when Leo reaches its greatest height above the horizon.
Most Leonids are after-midnight creatures, but the shower also features earthgrazers, long-lasting meteors that stream up from below the horizon, even before Leo rises, and make long passes across the sky. Though few in number, they can be spectacular. Keep an eye out for these if you’re out Monday night — they’ll stream upwards from the northeast starting roughly around 10 p.m. local time.
Bright meteors are produced when something the size of a Grape Nut (cereal) strikes the atmosphere at high speed. A fast moving particle possesses a great deal of kinetic energy, the energy of motion. (Bob King)
The particles left by the comet, called meteoroids, are quite small, ranging in size from 1 millimeter to 1 centimeter (about 1/2-inch) across. Most are the size of beach sand. Once upon a time, they were all embedded in the icy nucleus of Comet Tempel-Tuttle, but during each pass of the sun, some of that ice vaporizes (sublimes is the technical term) and releases the dust into the comet’s orbital path. Little pieces make fainter meteors while ones the size of Grape Nuts put on quite a show. Even small bits of rock can pack a punch when they’re moving extremely fast, and the Leonids are among the fastest meteors known.
Leonid meteors point back toward the radiant as illustrated in this photo of a Leonid meteor in 2001. (Bob King)
You can always tell a Leonid from a random or sporadic meteor by tracing its trail back to the head of Leo, the site of the radiant. If a meteor points back in another direction, it’s called a sporadic. The radiant is nothing more than a perspective effect: the meteoroids are all arriving on parallel paths, but our motion through them — like driving through a snowstorm at night — makes the particles appear to stream from a preferred direction.
The beauty of meteor-shower watching is that you don’t need any special equipment. Dress warmly, including lined boots, and relax in a reclining chair under a thick blanket in as dark a place as possible. No moon will mar the shower this year, so at least that’s not a concern. I like to turn my chair to face southeast for the Leonids. Then just look up and let time go by. Again, this is NOT a rich shower like the Perseids or Geminids, but you should see a few flaming flakes of 55P for your troubles.
You’ll also get to enjoy a wide-open view of the heavens overhead. During the wee hours, the winter constellations will be sliding off to the west, with the new spring constellations slowly taking over the eastern sky. Watch for Venus to rise around 5-5:30. Spend at least an hour with the shower. I invariably spend longer because I’m always hoping to see “just one more” before calling it quits. I like the dissonance between the slow slide of the constellations caused by Earth’s rotation compared to the momentary appearance of a meteor.
This is a screen grab from the Livemeteors.com site. (Bob King)
A final thought. If it’s cloudy that morning, you can observe the shower instead with your ears. It’s true. You can actually listen to the meteor shower at Livemeteors.com. When a particle tears across the atmosphere, it bumps into a lot of atoms and strips them of their electrons, briefly creating a streak of ionized air that reflects radio waves. The owner of the site has set up an antenna and receiver to record the sound of passing meteors. Just click the play arrow, and you can listen in real time.
Each meteor emits a low whistle. Check it out; it’s really cool. You can listen anytime because meteors happen nonstop, but the number should go up during the shower.
Clear skies (and ears)!
“Astro” Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.