As Comet ISON heads toward its closest approach to the sun—known as perihelion—on Nov. 28, 2013, scientists have been watching through many observatories to see if the comet has already broken up under the intense heat and gravitational forces of the sun. The comet is too far away to discern how many pieces it is in, so instead researchers carefully measure how bright it is, which can be used to infer its current state. Less light can sometimes mean that more of the material has boiled off and disappeared, perhaps pointing to a disintegrated comet. But also a disintegrating comet sometimes gives off more light, at least temporarily, so researchers look at the comet's pattern of behavior over the previous few days to work out what it may be doing.
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