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The Comet - Main features and scales
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The Comet - Main features and scales

October 15, 2009
This is slide 3 of 12 from the second Giotto slide set. The following caption is the one originally provided with the slide set.

As shown in this illustration, there exist two types of'cometary tails. Type-l-tails are ion tails and Type-ll-tails are dust tails. The Type-l-tail is the straight tail, often structured by fine, linear streamers or 'rays'. The spectra show distinct emission lines in- dicating that they are composed mostly of ionised gas. The dust of Type-ll-tails are usually broad, diffuse and curved. Their spectra show only the reflected spectrum of the Sun. This indicates that they are not composed of gas atoms and molecules that absorb or give off their own characteristic light, but that they are composed of dust grains that scatter the sunlight.