FIREBALL ALERT: During the next 48 hours, two big pieces of space debris are expected to re-enter Earth's atmosphere: a 2000 kg Centaur rocket body on Feb. 3rd and a 2500 kg Delta III rocket body on Feb. 4th. People living along the reentry ground tracks should be alert for fireballs. Ground tracks: Centaur, Delta III. More fireballs: Jan. 27, Jan 23, Jan 17, 2009; Dec. 29, 2008 ANATOMY OF A COMET: Backyard astronomers watching Comet Lulin approach Earth are getting a nice lesson in the anatomy of comets. Regard this photo taken Feb. 2nd by Italian observer Rolando Ligustri: The green ball in the middle is the comet's atmosphere or coma. It measures about 500,000 km across, more than three times wider than the planet Jupiter. The coma is richly laced with cyanogen (CN) and diatomic carbon (C2), two gases that glow green when exposed to sunlight in the near-vacuum of space. To the right of the coma is the comet's ion tail. It is a wispy streamer of ionized gas pushed away from the comet by solar wind. The ion tail points almost directly away from the sun. To the left of the coma is the comet's dust tail. Like Hansel and Gretel leaving bread crumbs to mark their path through the forest, Comet Lulin is leaving a trail of comet dust as it moves through the solar system. Compared to the lightweight molecules in the ion tail, grains of comet dust are heavier and harder for solar wind to push around. The dust tends to stay where it is dropped. The dust tail therefore traces the comet's curved orbit and does not point directly away from the sun as the ion tail does. Because the two tails point in different directions, they are called the "tail and anti-tail." More anatomy may be found in the gallery: UPDATED: Comet Lulin Photo Gallery [Comet Hunter telescope] [sky map] [ephemeris] ISS SKY SHOW: North Americans, be alert for spaceships after sunset. The International Space Station is making a series of bright flybys over the USA and Canada this week. Here, photographer Ken Scott points it out sailing over the frozen shores of Lake Michigan on Feb. 1st: "I recorded the event as a series of still images and stitched them together to make a movie," says Scott. Click here to watch it on YouTube. The ISS is about as bright as Venus and it is easy to see even before the twilight sky fades to black. Check the Simple Satellite Tracker to find out when to look. more images: from Phillip Chee of Peterborough, Ontario, Canada; from Christopher Calubaquib of El Sobrante, California Jan. 2009 Aurora Gallery [Previous Januaries: 2008, 2007, 2005, 2004, 2001] Explore the Sunspot Cycle |