Giant snowballs from space for Christmas
Is there a new Christmas star on the horizon?
I love the run up to Christmas for various reasons (mulled wine and panettone notwithstanding!) but one of the main reasons is that the skies are darker for longer, bringing out the best of British astronomy. However, in the run up to Christmas 2013 we have a special treat in store for us.
As this article is written there is a giant snowball hurtling towards us, well, the Sun. Comet C/2012 S1, more famously known as Comet ISON (International Scientific Optical Network), will reach perihelion on the 28th of November and should be observable in early December as ‘the comet of the century’!
ISON was discovered in September 2012 by two Russian scientists Vitali Nevski and Artyom Novichonok using an automated program that looks for asteroids. Many follow-up observations were made soon after and excitement about the comet grew steadily.
Comet ISON is a few km in diametre so it is not very large. The dust and water production are increasing slowly which is thought to be because ISON is a slow rotator (ref @nickastronomer).
At perihelion is will come as close as 1.6 million km from the surface of the Sun. At closest approach to the Earth it will reach 64 million km on the 26th of December so we certainly don’t need to worry about calling Bruce Willis or Elijah Wood on Boxing Day!
If ISON survives being so close to the Sun, when it passess the Earth in early December we should be able to see it during the daytime with the naked eye. If it does survive it could be visible until early January 2014.
Comets reside in the outer Solar System in the Oort cloud and generally have very eliptical orbits. This means that they take tens of years to revisit the Earth and during each orbit there are chances that the comet could become destroyed by being too close to the Sun.
Comets are massive dirty snowballs containing water, organic materials, ammonia and carbon. They are thought to have brought about the distruction of the dinosaurs and could have been the vehicle that brough water, or even life, to a once barren Earth.
These dirty snowballs have a nucleus that is dark due to the carbon compounds, but as the comet hurtles towards the Sun the ices begin to melt and some of the material becomes ionised. This leads to the two beautiful tails that make the comets visitble and individual. The word comet means ‘hairy star’ and comets have been observed since the early 1000s. It is even possible that the Christmas star was a comet!
ISON has been called the comet of the century as, if it survives perihelion, the comet could outshine the full moon. At the moment there is about a 50% chance that the comet will survive and give us some fantastic Christmas fairy lights so fingers, toes and anything else crossed that we all get to witness this spectacular astronomical phenomenon!
One of my favourite science ‘party tricks’ is to make a comet in a bucket. I’ve made comets in classrooms, pubs and theatres and every time I’m amazed at the Earth-bound analogy – just get in touch if you want me to come and visit!
Me on the Naked Scientists telling you how to make a comet:
A video of me making a comet: