Hubble's new image of Comet ISON shows the comet streaking across space on its course toward the Sun. It's a beautiful picture, and it lets us know that a.) ISON doesn't appear to be shattering and b.) ISON's jet seems to have vanished. But how do we get that information from the picture you see below?
Comet expert (and blog guest contributer!) Dr. Jian-Yang Li created a mathematical computer model of Comet ISON's coma — the fuzzy, spherical cloud of material that forms around a comet's nucleus when it nears the Sun — using the latest Hubble data. By subtracting that model from the reality of the data, we can see where the two differentiate.
It's best explained with a metaphor. Imagine you have a hill. The hill has an overall shape, but it also has bumps that may be difficult to see.
Now imagine you could create a hill that is the same shape, but without the bumps. If you could use that model of the hill to subtract the overall shape of the hill, all that would be left behind are the bumps, which are then quite obvious. We then exaggerate the bumps — ...