Transcontinental jets used the sky as a chalkboard yesterday afternoon. Three planes moving along different paths left contrails that intersected to create at least two letters of the alphabet, parallel lines and a right triangle. The lesson happened about an hour before sunset when the trails stood in bold contrast against a deep blue sky.
Contrails are formed when warm water vapor in plane exhaust condenses into droplets or ice crystals in the chilly upper atmosphere. It’s analogous to seeing your breath on a cold day.
That’s not all that’s been streaking through the sky lately. Earlier this week on the night of the 11th, an extremely bright fireball flashed across the sky around 8:50 p.m. CST over Jackson, Miss. It was witnessed by many observers across the South. NASA astronomer Bill Cooke of the Meteoroid Environment Office of Marshall Space Flight Center confirmed the sighting, reporting that a station in Canada that monitors infrasound – sounds below the level of human hearing – picked up the signal of the meteor an hour and 20 minutes after the flash. Infrasound is used to monitor big events at large distances like earthquakes, nuclear bomb tests and occasional meteors entering the atmosphere. Whales and other animals use it to communicate.
“The infrasound signal at ELFO (Elginfield Infrasound Array) lasted some 2.5 minutes, and the amplitude permits an estimate of the meteor’s energy at 40-80 tons of TNT. If we assume a speed of 15 kilometers per second, we can derive a mass of 171 kg or 376 pounds. Making a further assumption that the meteor was porous rock gives a size, or diameter, of 0.54 meters or 21 inches,” according to Cooke.
Here’s a video that shows the meteor flash recorded by a surveillance camera in Louisiana. Amateur meteorite hunter Jake Schaefer from the Los Angeles area has been studying Nexrad Doppler radar data used by meteorologists at the time of the fireball’s fall and found a couple ‘hits’ which might indicate that pieces survived to land as meteorites. His latest plots, based on radar data, surveillance cameras, sonic booms and eyewitness reports, show the meteor’s possible track over the ground southwest of Jackson. More details and videos can be seen on his blog as well as read more details. Check out NASA’s Fireballs archive, too for other recent meteor videos.
Exactly where it landed is unknown, but a ground track is a great place to start. Similar radar data was used to help pinpoint the ground track and hence potential landing sites for meteorite fragments from last spring’s Mifflin fall over southwestern Wisconsin. Using the data and eyewitness reports, hunters found nearly 8 lbs. of fresh, black-crusted meteorites. Let’s hope it happens again down South.
Not only are meteorites falling to Earth with regularity, but the sun recently experienced a storm of comets. Scientists and online comet hunters have discovered 2000 comets (as of Dec. 26, 2010) in the space-based observatory’s images since it began operation in 1995. Most of these belong to the Kreutz family of comets called ‘sungrazers’. They’re believed to be fragments of a much larger comet seen in the 12th century that broke up during a close pass of the sun.
But something odd happened in late December last year. The usual rate of one comet showing up every few days octupled to 25 comets in 10 days:
“The storm began on Dec 13th and ended on the 22nd,” says Karl Battams
of the Naval Research Lab in Washington, DC. “During that time, the
Solar and Heliospheric Observatory (SOHO) detected 25 comets diving into
the sun. It was crazy!”
Sungrazers are seen regularly by SOHO as they first brighten, then break up and vaporize in the sun’s intense heat. Astronomers aren’t sure what to make of the ‘storm’, but the number of comets recorded by SOHO has risen from 69 in 1997 to 200 in 2010. Comet lovers are hoping that the increase could mean we’re due for a good-sized sungrazer that will survive the sun’s intense heat and appear as a brilliant object at dusk or dawn. No one knows when the next one is due, so it’s wait and see for now.