Sunlight ionizes the ejected gas molecules, causing then to glow with a bluish color. The solar wind carries this ionized gas away from the comet, creating a straight, bluish gas tail. The ejected dust gets pushed away from the Sun more gently, so it forms a curving tail. The dust particles simply reflect sunlight, so the dust tail has a white to pale-yellow color.
Although October marks the peak for Comet 103P/Hartley, the comet will continue to make news in November. NASA's EPOXI mission will fly past the comet and return stunning images of its nucleus. EPOXI comes closest to the comet November 4, and NASA should release fresh images soon thereafter.
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