how long is the tail of such a visible comet?

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This is one of the more interesting facts about comets; the tail always points away from the Sun. This is because of solar wind where particles from the Sun collide with the material coming from the comet interior. As the comet approaches the Sun the inner volatiles melt are escape into space. This process is called sublimation. As the solar wind hits this material, it pushes away from the solar source.

Comets typically have not one but two tails. An example can be found here:

http://antwrp.gsfc.nasa.gov/apod/ap091216.html

While impressive a comet appearing in the night sky implies something about its scale. When Hale Bopp came through it could be seen quite well. So how long is the tail of such a visible comet? Compare that to the average distance between Earth and the Sun.

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