From the Independent in the UK (
http://www.independent.co.uk/news/science/brighter-than-a-full-moon-the-biggest-star-of-2013-could-be-ison--the-comet-of-the-century-8431443.html). While not a radio event per se, it will garner headlines for sure next year and our telescope will be up and operational for this celestial event.
A comet discovered by two Russian astronomers will be visible from Earth next
year. Get ready for a once-in-a lifetime light show, says David Whitehouse.
At the moment it is a faint object, visible only in sophisticated telescopes
as a point of light moving slowly against the background stars. It doesn't seem
much – a frozen chunk of rock and ice – one of many moving in the depths of
space. But this one is being tracked with eager anticipation by astronomers from
around the world, and in a year everyone could know its name.
Comet Ison could draw millions out into the dark to witness what could be the
brightest comet seen in many generations – brighter even than the full Moon.
It was found as a blur on an electronic image of the night sky taken through a telescope at the Kislovodsk Observatory in Russia
as part of a project to survey the sky looking for comets and asteroids – chunks
of rock and ice that litter space. Astronomers Vitali Nevski and Artyom
Novichonok were expecting to use the International Scientific Optical Network's
(Ison) 40cm telescope on the night of 20 September but clouds halted their
plans.
It was a frustrating night but about half an hour prior to the beginning of
morning twilight, they noticed the sky was clearing and got the telescope and
camera up and running to obtain some survey images in the constellations of
Gemini and Cancer.
When the images were obtained Nevski loaded them into a computer program
designed to detect asteroids and comets moving between images. He noticed a
rather bright object with unusually slow movement, which he thought could only
mean it was situated way beyond the orbit of Jupiter. But he couldn't tell if
the object was a comet, so Novichonok booked time on a larger telescope to take
another look. Less than a day later the new images revealed that Nevski and
Novichonok had discovered a comet, which was named Comet Ison. A database search
showed it has been seen in images taken by other telescopes earlier that year
and in late 2011. These observations allowed its orbit to be calculated, and
when astronomers did that they let out a collective "wow."
Comet Ison has taken millions of years to reach us travelling from the
so-called Oort cloud – a reservoir of trillions and trillions of chunks of rock
and ice, leftovers from the birth of the planets. It reaches out more than a
light-year – a quarter of the way to the nearest star. In the Oort cloud the Sun
is but a distant point of light whose feeble gravity is just enough to hold onto
the cloud. Every once in a while a tiny tug of gravity, perhaps from a nearby
star or wandering object, disturbs the cloud sending some of its comets out into
interstellar space to be lost forever and a few are scattered sunward. Comet
Ison is making its first, and perhaps only visit to us. Its life has been cold,
frozen hard and unchanging, but it is moving closer to the Sun, and getting
warmer.
Ison's surface is very dark – darker than asphalt – pockmarked and dusty with
ice beneath the surface. It's a small body, a few tens of miles across, with a
tiny pull of gravity. If you stood upon it you could leap 20 miles into space
taking over a week to come down again, watching as the comet rotated beneath
you. You could walk to the equator, kneel down and gather up handfuls of comet
material to make snowballs, throw them in a direction against the comet's spin
and watch them hang motionless in front of you. But it will not remain quiet on
Comet Ison for the Sun's heat will bring it to life.
By the end of summer it will become visible in small telescopes and
binoculars. By October it will pass close to Mars and things will begin to stir.
The surface will shift as the ice responds to the thermal shock, cracks will
appear in the crust, tiny puffs of gas will rise from it as it is warmed. The
comet's tail is forming.
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.
Remarkably Ison might not be the only spectacular comet visible next year.
Another comet, called 2014 L4 (PanSTARRS), was discovered last year and in March
and April it could also be a magnificent object in the evening sky. 2013 could
be the year of the great comets.
As Comet Ison heads back to deep space in 2014 the sky above it would begin
to clear as the dust and gas geysers loose their energy. Returning to the place
where the Sun is a distant point of light, Comet Ison may never return. Its tail
points outward now as the solar wind is at its back, and it fades and the comet
falls quiet once more, this time forever.
Dr David Whitehouse is an author and astronomer
