Comet ISON is out in the early morning sky. Back in 2012 when it was discovered, at the International Scientific Optical Network (ISON) in Russia, the hopes were that it would be a bright and impressive comet. As it has gotten closer expectations have been scaled back. But just recently the brightness increased and it has now become visible to the naked eye.
It is whipping toward the Sun with the closest approach to the Sun expected for the 28th or Thanksgiving. (Closest approach is called perihelion.) Just before that the comet might become very bright, though with a close approach to the Sun might also destroy the comet. We'll just have to wait and see. If Comet ISON survives it will swing away from the Sun and may potentially have a long tail making it even more visible. Though it will be moving away from the Sun and begin growing dimmer. Though it might still be visible until about January.
Like all comets predicting it's appearance is difficult. Mainly this is due to the fact that it is difficult to know what a comet is made of. The tail and the visible parts are generally gas and small particles and the core can be rocks or frozen gases or a mixture of both. When the comet is heated up by the Sun, the gases come off and create a cloud known as the coma. Then pressure from the Sun in the form of both solar radiation and solar wind push against the coma to create a tail out behind the comet.
Now ISON made news recently since the comet was appearing green. This isn't rare for comets and is likely due to the chemical makeup of the gases forming the comet. In particular, cyanogen, a poisonous gas and diatomic carbon, which are both common in comets glow green when exposed to the Sun's energy. Both cyanogen and diatomic carbon have carbon which is necessary for life as we know it. And comets are often considered a source for some of the carbon that is found on Earth because of comet impacts during the formation of the Earth about 4 billion years ago. (A source of the building blocks of life, not life itself.)
But we don't have to worry about Comet ISON. Even if it is difficult to predict what a comet will look like, we don't have the same problem with predicting its path. So no comet impact for Christmas. We're just going to have to hope that ISON will continue to brighten. Hopefully in early December when the comet will be visible both in the morning before sunrise and in the evening just after sunset, we'll all get a chance to see it.
And if we get to see it, think back to when comets were considered omens, which for some folks might be right now, and consider how much comets still have to teach us about the origin of the Solar System. There's still a lot to learn. And are still people out there wanting to learn it. To me that's a good omen.
For more information about viewing the comet check out http://isonatlas.wordpress.com/december-2013/.