Thought I’d tease you with a recent photo of a bright Perseid meteor. It was taken at dawn on Aug. 4 at Chumack Observatory using a video camera. Click HERE to see a movie of highlights from the video feed. You might be surprised at how little it takes to make a spectacle when it comes to meteors.
The Perseid meteor shower, which peaks on the the mornings of August 12 and 13, produces meteors ranging in brightness from telescopic to brighter than Venus. Traveling at 41 miles per second (66 km) guarantees a lot of bang for your buck. At that speed even a small grain can create a brilliant streak of light when it slams into the atmosphere.
To give you an idea, here’s a table comparing meteoroid size and brightness for Perseid meteor shower members (source M. Campbell-Brown, P. Brown). The brightness estimates are for meteors hitting the atmosphere directly overhead at an altitude of 62 miles (100 km). Weights are in grams; one ounce weighs 28.3 grams:
* 1/1,000 gram (weight of the smallest snowflake or seven grains of fine sand) = magnitude 3 or one brightness level fainter than the Big Dipper stars
* 1/100 gram (four grains uncooked rice) = magnitude 0.5 or similar to the bright star Vega
* 1/10 gram (a toothpick) = -2 magnitude or a little fainter than Jupiter
* 1 gram (the cap of a pen, metal paperclip) = -4 magnitude and similar to Venus
* 10 grams (a pencil or two nickels) = -7 magnitude and bright as the thick crescent moon
Perseids are zippy. Slower meteors like the Geminids that light up December nights are breeze in at a mere 22 miles per second (35 km). A 1/10 gram Geminid meteoroid shines weakly at 3rd magnitude compared to a similar-sized Perseid. That’s at least part of the reason why the Perseids are famous for their fireballs - meteors the equal of Venus or brighter.
Speedy motion (kinetic energy) is transformed into the energy that creates the light streak and vaporizes the cookie-crumb meteoroid. Faster-moving meteoroids possess more kinetic energy and flare more brightly. Now you can see why even the small and meek can wow us skywatchers.
While we’re on meteors, it’s good to remember that most originate as dust boiled off comets by the sun. The Perseids originate from Comet 109P/Swift-Tuttle which swings around the sun every 133 years. Each August, Earth passes through the comet’s orbit; any bits of Swift-Tuttle in our path get fried by our atmosphere.
No bright comet currently graces the August sky. Comet C/2012 F6 Lemmon remains the best of the bunch, still shining at a respectable 10.5 magnitude; it looks like a fuzzy blob with a short southward-pointing tail in 8-inch and larger telescopes.
Amateur astronomer Rolando Ligustri recently took a beautiful portrait of Lemmon as it passed near the star Beta in Cepheus the King. The image reminds us of the dynamic process that cycles meteors to Earth’s skies by way of dust shed from comet tails.