April showers usually bring clouds, but let's hope they stay away Thursday morning, April 22nd. That's when the annual Lyrid meteor shower peaks, with 15-20 sparks of incinerating comet dust visible per hour from a dark sky. The last shower, the Quadrantids, occurred in early January, making the Lyrids as welcome to meteor-starved eyes as spring rain on parched ground.
The Lyrids get their name from Lyra the Harp, home of Vega, one of the brightest stars in the sky.. Showers are named for the constellation they shoot out of. Perseus is home to the Perseids and Orion to the Orionids.
Before the constellations boundaries were fixed in 1930, the border between Lyra and neighboring Hercules the Strongman was vague and contested. Since Lyrid meteors stream from a point in the sky just 8° southwest of Vega, it made sense to associate the shower with Lyra. But when the new boundaries went up, the Lyrids ended up in Hercules. Rightfully, we should call them the Herculids, but that's as likely to happen as the U.S. adopting the metric system. Lyrids it is!
When you spot a Lyrid meteor you're seeing an incandescent bit of sand or chocolate-chip-size rock fragment shed by Comet Thatcher, discovered by A.E. Thatcher in May 1861. The comet takes 415 years to go around the sun and won't return to the inner solar system until around 2283. Each time it passes the sun, a portion of its dust-laden ice vaporizes, depositing debris along its orbital path. Every year in late April, Earth's orbit intersects with Thatcher's and we plow headlong into the comet's cast-offs at a fearsome 108,000 miles an hour (48 km/sec).
As each grain or small rock slams into the atmosphere it glows white-hot from friction and quickly turns to soot. At the same time, its passage excites (ionizes) the air molecules along its path. When they relax back to their previous "unexcited" state, they radiate light. Both the glowing, hot particle and the trail of ionized air are responsible then for the familiar streak of a meteor.
The average width of the streak is about about three feet (1 meter) with a length tens of kilometers long. Picture an incandescent rock no bigger than a tick traveling 200 times faster than a jet airplane at the center of a self-created tunnel of glowing air — that's a meteor. As a side note, I can't think of a better way for a tick to die.
Meteors can be colorful. Blue and green arise from heated iron and magnesium in the particle itself, while oxygen and nitrogen in the atmosphere are responsible for the orange and red hues we see.
Watching meteor showers is easy. No equipment is needed other than a lounge chair and warm clothes. Plan to spend an hour or more relaxing under the stars with the Summer Triangle yawning overhead..
Face in whatever direction is darkest for the best view. You can also tilt the chair back to look directly overhead. You'll know you're seeing a Lyrid if its trail leads back toward Vega. Shower meteors all travel on parallel trajectories, so they seem to arrive from the same point in the sky called the radiant. Parallel railroad tracks that appear to converge to a point in the distance also demonstrate the same perspective effect.
Unfortunately, the waxing gibbous moon will interfere with the shower this year. It sets around 4:15 a.m. local time, leaving only about a half-hour of true, dark sky before the start of morning twilight. To make the best of the show I suggest watching between 3 and 5 a.m. local time Thursday. Moonlight will reduce the number of meteors visible to perhaps 10 per hour, but conditions will gradually improve as the moon drops closer to the horizon and then sets.
The forecast is for clear skies where I live. I hope you have the same so we can enjoy it together in spirit.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.