Here's an old article from several years ago from a previous incarnation of TDG.
The noun comet derives from Aster Kometes, the Greek for Hairy Star. Well, all innuendo aside, and, indeed, references to Captain Caveman, Greek Waiters and Lounge Singers, the Ancient Greek astronomers named the phenomenon well.
According to Fred Whipple, from whom the dirty snowball comet theory originated, comets are composed of a nucleus usually around 5 to 10 Km in diameter, irregular in shape, and made of a loose agglomeration of ice, rock and hydrocarbons. The nucleus is surrounded by a diffuse atmosphere of material called a coma that can expand to up to 250000 km in diameter on close approach to the sun to form little more than vacuum, and they have highly elliptical orbits. On approach to the sun, as the theory goes, the nucleus gives off jets of gas and after streamlining by the solar wind a tail forms. The tail itself is a complex beast and is sometimes comprised of two basic parts. Oddly enough, there can be a third tail of sorts, called an anti-tail, which is seen to be orientated towards the sun, hence the name. The explanation of this anti-tail is either it is an optical illusion through perspective, or it is a real phenomenon made up of material spewed out by the comet a long time in advance of its perihelion.
Given the above it follows that there is absolutely no connection whatsoever between this comet and the sun, and this comet and the sun, and this comet and the sun, and this comet and the sun, and this comet and the sun, and this comet and the sun.
Yet, it is also quite clear that as those comets pass the sun, there is a brightening of coronal prominences and, in some cases rather violent ejections of material. Now, if comets are generally 10km or so in diameter then gravity could not be brought in as an explanation of why there might be such a violent connection between the sun and these comets. Indeed, nor could the occasional comet crashing into the sun, for in that case one would expect such a small cosmological body to be utterly incinerated by the corona with little or no subsequent reaction - a kind of fizzling out. If comets are just dirty snowballs, as Fred Whipple would have it, then there is also no way there can be a connection between the ejective prominences and the sun. So, what does that leave us with? Well, it is obvious. There is no connection whatsoever, just as I stated above. These short movies are just a lesson in coincidence, or at best they are an example of a triggering phenomenon in which the comet has just enough gravitational attraction, which merely accelerates a usual function of the sun. Of course, that would be special pleading.
Well, let us explore this from another angle. Let us suppose there is a connection between the sun and these comets. Let us first suppose that a gravitational phenomenon is at work. Well, if these comets are just 10km in size, or thereabouts, then they cannot really be made out of ice, rock and hydrocarbons. They must be made of a material a great deal more dense than that required by the dirty snowball theory. But let us suppose that the dirty snowball theory is correct as to the composition of these comets. Well, it follows that if there is a gravitational connection between the comets and the sun then these comets are much greater in size than 10 km in diameter. It would be more sensible to consider them on the order of the size of the Moon or Mercury at the very very least, making them of a planetary scale. Now, that is, of course, completely absurd. No comet could really be that size, now could it? Well, until fairly recently it would have been considered absurd by most. And yet, Neil Tyson, director of the Hayden Planetarium at the American Museum of Natural History calls Pluto "King of the Kuiper Belt Comets"
So, it certainly can’t be that absurd to consider Pluto a comet – at least, if it were, Neil Tyson would have been unwise to risk his high status job over it. So, we have Pluto, somewhat politically, demoted from the status of a planet to the status of a comet – does Pluto care how the mighty fall? Pluto once considered the ninth planet, and still is considered so outside academic circles, to be now considered a comet implies that comets can be of a planetary scale, albeit one of the minnows. After all, one can only confuse things that are similar, even if you mistake your wife for a hat. Regardless of how one chooses to categorise the objects of the solar system, we have here a public acceptance that comets can be pretty damn big, pardoning my lack of clarity here, and that they can be spherical, indeed planet-like enough to be hazily referred to as a planet. But wait a minute? Didn’t some over-educated madman refer to Venus as a comet? Ah yes, Immanuel Velikovsky. The man who is probably, single-handedly, responsible for the creation of CSICOP – don’t be swayed by their vaudeville fights with two-bit psychics – CSICOP exists to get the real threats to the contemporary order, that is, individuals of an intellectual pedigree with something that is so missed in much of the scientific world - creativity. Quite why, if science is self-correcting, which it is according to its rich history, they should be required at all is not clear, since their methods and manner are typically unscientific and have more in common with Tony Clifton than Michael Faraday. So, Velikovsky considered Venus as a comet. Venus is larger than Pluto, but should that put us off thinking of Venus as a comet? Well, not anymore. But there was one crucial difference between Venus and Pluto. Venus isn’t an Ice Whipple, it’s more like a Hot Fudge Sundae, well, maybe just Hot Fudge.
But now let us suppose that these comets really are the size that they are claimed to be, namely around 10 Km in diameter and we also accept that they are of too low a density to have any significant gravitational effect. So, what does that leave us with? Well, one could take the view of a couple of Velikovsky’s intellectual successors, Ralph Juergens and J.M. McCanney who suggest that the sun is electric and that comets are electric respectively. That sort of viewpoint could explain why there appears to be a connection between the sun and comets.
What would be really frightening would be if comets are of planetary scale on the order of Venus and have an electrical potential. Then perhaps we’d be knee deep in trouble now and again. But Velikovsky thought that had already happened, and as we all know he was just nonsensical. Lucky for us.