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Caption: Spitzer 22 µm imagery of comet 103P/Hartley 2. Each image shown is registered and added stack of 200 individual exposures. The compass in the lower left indicates equatorial north (N), equatorial east (E), and the direction to the Sun ☉, the expected direction of the comet's motion from its ephemeris (µ), and the negative heliocentric velocity vector (-ν). The two images show the same patch of sky and the comet is identified through its apparent speed and direction of motion. Along with the comet's nucleus, the trail was detected as a linear feature lying along the PA of -ν, 271°. The comet's tail, had it been present, would have been aligned closely to the projected anti-solar direction of 110° PA.
Credit: NASA/JPL-Caltech/C.M. Lisse