但一些彗星的彗发宽度可达将近100万英里(160万公里)，一些彗尾长度则可达1亿英里(1.6亿公里)。
Some comets have comas that can reach nearly 1 million miles (1.6 million kilometers) wide, and some have tails reaching 100 million miles (160 million kilometers) long.
从太阳而来的辐射，将尘埃粒子吹离彗发，形成尘埃彗尾；同时，来自太阳的带电粒子将一些彗星气体电离成离子，形成离子彗尾。
Radiation from the sun pushes dust particles away from the coma, forming a dust tail, while charged particles from the sun convert some of the comet's gases into ions, forming an ion tail.
很多彗星接近太阳时，我们可以用肉眼看见，因为它们的彗发和彗尾可以反射阳光，甚至因为受阳光激发而自发光。
We can see a number of comets with the naked eye when they pass close to the sun because their comas and tails reflect sunlight or even glow because of energy they absorb from the sun.
明显地，离子彗尾轻易伸展至背景星团NGC 1245（上左）的前面，在飞马座，离彗星可爱的绿色彗头或彗发1.5度。
Remarkably, the ion tail easily stretches past background star cluster NGC 1245 (upper left) in the constellation Perseus, about 1.5 degrees from the comet's lovely greenish head or coma.
彗星气态彗发里的分子被阳光激发而发光。
The molecules of the comet's gaseous coma fluoresce in sunlight.
彗星气态彗发里的分子被阳光激发而发光。
The molecules of the comet's gaseous coma fluoresce in sunlight.
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