This image from Michael Jager of Jauerling, Austria – taken on November 10, 2013 – clearly shows that Comet ISON now has not one but two tails. That’s a sign that the comet is drawing closer, and closer, to the sun that binds it in orbit. Comet ISON will be closest to the sun by the end of this month, on November 28, 2913.
One tail – called the ion tail – is composed of ionized gas molecules. The solar wind, charged particles flowing fast from the sun, creates the ion tail as the solar particles interact with gases from the comet’s nucleus, or core.
Then there is also the dust tail. It’s simply bits of dirt from the comet’s nucleus, which are being pushed away by light pressure from the sun.
No matter where the comet is in orbit, the ion tail points almost directly away from the sun. But the dust tail doesn’t. As explained on the great website spaceweather.com:
… ISON is leaving a trail of comet dust as it moves through the solar system. Compared to the lightweight molecules in the ion tail, grains of comet dust are heavier and harder for solar wind to push around. The dust tends to stay where it is dropped. The dust tail, therefore, traces the comet’s orbit and does not point directly away from the sun as the ion tail does.
It’s this divergence of the two tails – one pointing almost directly away from the sun and the other not – that allows us to see them both.
Thank you, Michael Jager, for this photo!