Comet Ison will pass closest to the Earth next year, and it could be brighter than a full moon when it does.
(NASA APOD/Ligustri Rolando)
Earthlings can expect quite the lightshow in 2013, thanks to the impending arrival of a newly discovered comet, expected for a spectacular flyover next December.
The comet Ison, a chunk of ice and rock hurtling toward the sun from out somewhere near Jupiter, could be the brightest in living memory.
"Comet Ison could draw millions out into the dark to witness what could be the brightest comet seen in many generations--brighter than even the full moon," said astronomer David Whitehouse, writing for the Independent.
Ison was discovered back in September, when a team of Russian astronomers spotted a faint blur in the vicinity of the Gemini and Cancer constellations, and confirmed by sifting through images from the past year, NASA said. It likely broke free from the Ort cloud, a field of endless bits of rock and ice leftover from the formation of planets.
The comet will become visible to small telescopes and binoculars by the end of summer, and pass by Mars in October. The tail will begin to form as it gets nearer to the Sun, with thermal heat warming the ice and releasing puffs of gas, and then:
Slowly at first but with increasing vigour, as it passes the orbit of Earth, the gas and dust geysers will gather force. The space around the comet becomes brilliant as the ice below the surface turns into gas and erupts, reflecting the light of the Sun. Now Ison is surrounded by a cloud of gas called the coma, hundreds of thousands of miles from side to side. The comet's rotation curves these jets into space as they trail into spirals behind it. As they move out the gas trails are stopped and blown backwards by the Solar Wind.
By late November it will be visible to the unaided eye just after dark in the same direction as the setting Sun. Its tail could stretch like a searchlight into the sky above the horizon. Then it will swing rapidly around the Sun, passing within two million miles of it, far closer than any planet ever does, to emerge visible in the evening sky heading northward towards the pole star. It could be an "unaided eye" object for months. When it is close in its approach to the Sun it could become intensely brilliant but at that stage it would be difficult and dangerous to see without special instrumentation as it would be only a degree from the sun.
Of course, it's impossible to tell how the "dirty snowball" might evolve between now and next year. It could be a total flameout--or it could be one of the great comets in hundreds of years.