Why Do Comets Have Tails?

课文

1. Comets are icy bodies that orbit the Sun in long, stretched-out paths.

   彗星是冰质天体，沿狭长轨道绕太阳运行。

2. When a comet approaches the Sun, its surface warms up and releases gas and dust.

   当彗星接近太阳时，其表面受热，释放出气体和尘埃。

3. Solar radiation and the solar wind push this material away from the nucleus.

   太阳辐射和太阳风将这些物质推离彗核。

4. The glowing gas forms an ion tail, which always points directly away from the Sun.

   发光的气体形成离子尾，始终背向太阳延伸。

5. The dust tail curves slightly because tiny particles respond to both sunlight and gravity.

   尘埃尾略呈弯曲状，因为微小尘粒同时受阳光和引力影响。

6. These tails can stretch millions of kilometers but remain extremely thin and faint.

   这些彗尾可绵延数百万公里，却极其稀薄暗淡。

7. A comet only develops visible tails when it is inside the orbit of Mars.

   只有当彗星进入火星轨道以内时，才会出现可见彗尾。

8. Once it moves farther out again, the ice freezes solid and the tails vanish.

   一旦它再次远离太阳，冰重新冻结，彗尾便消失。

9. This process repeats every time the comet returns on its orbital journey.

   每次彗星沿轨道回归时，这一过程都会重复发生。

10. So the tail isn’t left behind—it’s freshly made each time the comet gets warm.

    因此彗尾并非被‘甩在身后’，而是每次受热后新生成的。