評論
打印
Comet
彗星
Do you know what a comet is?
你知道彗星是什么嗎？
A comet is an object in the solar system.
彗星是太陽系中的天體。
It travels around the sun like the planets.
它像其它行星一樣繞著太陽轉。
Then, why don't we call it a planet?
那么，為什么我們不把它叫做行星？
Because comets are usually very small and their orbits are not regular, they cannot be planets.
因為彗星通常很小，而且它們的軌道還不規則，所以它們不能成為行星。
Because their orbits are not regular, they sometimes crash into planets and disappear.
因為它們的軌道不規則，有時撞上行星后就消失了。
So, it is very hard to observe comet in the sky.
因此，很難在空中觀測彗星。
However, there are some comets we can observe.
然而，有些彗星我們能觀測到。
For example, Halley's comet is very famous.
例如，哈雷彗星就非常著名。
Every 75 or 76 years, we can see it in the sky.
每隔75或76年，我們就能在空中看到它。
So, if you live very long, you can see Halley's comet more than once.
因此，如果你的壽命很長，你就會不止一次能看到哈雷彗星了。
