A nice photograph of the separate tail and nucleus is found at: http://cmarchesin.blogspot.com/2007/11/beautiful-blue-ion-tail-comet-holmes.html.

The tail of the comet points behind its nucleus and away from the Sun and Earth. The colors are caused by ions (charged particles) coming from the comet and fluorescing (emitting radiation [light]) from its interaction with the Sun. Specifically, the greenish colors of the nucleus are caused by charged particles such as carbon ions and the bluish colors of the tail by carbon monoxide ions within the comet.

The comet is made up of pieces of ice, frozen gas, and tiny rocks and dust. However, when it approaches the Sun in its orbit around the star a comet begins to heat up (or sublimate) due to its cold surface getting closer to the heat of the Sun.

Material from the nucleus of the comet begins to be ejected from the dense nucleus. The gases and dust form a tenuous atmosphere or cloud (sometimes called the coma) around the nucleus. Since the comet has very little mass, it doesn’t have much gravity. Thus, it cannot keep these gases and dust near to it. The solar wind blowing past the comet throws off the material and it forms a gaseous (ion) tail behind it and curving away from the Sun.

Comet Holmes brightened a million of times over its normal brightness over the past several weeks due to some major event in the nucleus of the comet—possibly a collapse of some of the comet that was hollow or less dense than other portions, or a collision with another object.

When this happens the frozen gases heat up and are ejected, causing a tail to appear. Astronomers think that Comet Holmes may likely produce more tails and more dramatic pictures in the future.

Only time will tell what we will see as we observe Comet Holmes in the night sky.


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Astronomy  Comet  Sun  William Atkins