Hi Steve, that one had me going for a while too. But my guess is that the invisible cloud of ice crystals would have to come between us and tha sun. If you think abut the cloud as being in co-orbit with the comet, not a cloud in orbit around the comet then the flakes themselves are falling toward the sun, and the solar wind is acting with enough drag to slow them down just enough to keep them oriented. We should in theory be able to see a sun halo, or shaft if the sun is just about to move behind the "invisible cloud" that I imagine extends far beyond the periphery of the coma itself. In esscence we need to have a comet eclipse. Take another look at the street lights at the bottom of the page you with time hack 1:04:20 and imagine a night sky. Those pillars of light should only be able to go up 300 feet or so, which is the thickness of the fog. But they appear at times to be miles high when you see them from a distance and they appear shorter as you get closer and they change in length as you move up and down in altitude. It is very similar to the effect of the comet tail changing in length.

The biggest proof yet for the existence of my imaginary invisble cloud it the fact that the tail of the comet does not curve. If Ionizing gas being excited by radiation or sunlight is the real cause, it should appear curved by quite a big apparent arc. Similar to tracer rounds being fired into the night and then moving the barel of the gun just a little bit. In the or days it would take ionizing gas to move from the head of the comet to the end of multi million mile tail the coma has moved the angle a degree or two at least. The only answer is that the end of the tail is the same distance, or even closer to the observer than the beginning. The problem with my theory is that it is the wrong color. If it is an ice cloud the tail should be the same color as the coma. My answer is that instead of an Ice crystal of H20, maybe it is an ice crystal of some other gas. It is cold enough in space to freeze many different gasses, but that frozen gas would have to be nearly clear to prevent solar heating, allowing most of the energy to pass through without much heat.

As I said before, it is my theory, I don't know if anybody else has tried to proove or disprove it. But I would like to see an eclipse of the sun by a comet just for giggles.

Dan