Justin Tilbrook of Australia took a marvelous image earlier this week showing our two current comet celebs F6 Lemmon and L4 PANSTARRS together in the same picture.It’s not often you’ll see two tail-toting comets captured with a wide-angle lens at the same time.
To bring you up to date, Panstarrs is still visible very low above the horizon in morning twilight from far southern latitudes. This week it’s brightened to 4th magnitude and appears like a fuzzy pearl with a short tail. One observer noted a yellow color to the comet’s head caused by dust reflecting the ever-intensifying sunlight as PANSTARRS barrels sunward toward its March 10 perihelion.
Lemmon is higher up in the sky but fainter at magnitude 5.5. Right now it might be difficult to see with the naked eye because of moonlight. Binoculars show a bright head and a 1/2-degree-long tail.
You might be interested in a recent study on brightness predictions for comets L4 PANSTARRS and ISON by Ignacio Ferrin of the University of Antioquia in Medellin, Colombia. Here are the main points:
* C/2011 L4 Panstarrs will be less bright than Halley’s Comet was in 1986. It will show
a tail easily detectable with the naked eye.
* There’s a 75% chance that C/2012 S1 ISON will continue to brighten and put on a great show late this fall. Ferrin predicts it could become as bright as the full moon (magnitude -12.6) when nearest the sun. But his prediction comes with a caution: ISON will pass within the Roche Limit when it swings around the sun in late November. This is the minimum distance a smaller body can hold together in one piece while orbiting a larger body without being torn to bits by the larger body’s overwhelming gravity.
Ferrin writes: “Any object within this limit has a large probability of disintegrating due to differential gravitational forces from the Sun. The combinations of Roche’s Limit, plus solar radiation plus very high temperature, suggest that the comet may not survive its encounter with the Sun, disintegrating into several pieces. Or it may survive, if its internal cohesion is
sufficient to endure those conditions.”
If you’d like to learn more, please check out the complete study.