60 Comets-High

Comets FOCUS Question What are comets, and how do they move through the solar system?

彗星焦点问题彗星是什么，它们是如何在太阳系中移动的?

What Is a Comet? What is the difference between a comet and a big rock? Not much! Comets are icy rocks flying through space. They are best known for their long tails visible in the night sky. Comets have been around since the solar system formed 4.6 billion years ago. They are leftovers from materials that formed the planets. Their long orbits take them to the farthest reaches of the solar system and also bring them dangerously close to the Sun. Some comets orbit in the Asteroid Belt between Mars and Jupiter. But most come from much farther away. Beyond Neptune is the Kuiper (KY-pur) Belt. It contains billions of comets. Even farther out is the Oort Cloud. It is home to trillions of comets!

彗星是什么?彗星和大石头的区别是什么? 没有多少!彗星是在太空中飞行的冰冷岩石。 它们最著名的是在夜空中可见的长尾巴。 自从46亿年前太阳系形成以来，彗星就已经存在了。 它们是形成行星的物质的残留物。 它们的长轨道将它们带到太阳系的最远处，也使它们危险地接近太阳。 一些彗星在火星和木星之间的小行星带运行。 但大多数来自遥远的地方。 海王星之外是柯伊伯(KY-pur)带。 它包含了数十亿颗彗星。 更远的地方是奥尔特云。 它是数万亿彗星的家园!

Trips Around Sun The time it takes a comet to orbit the Sun is called a period. Short-period comets orbit the Sun in 200 or fewer years. They come from the Kuiper Belt. Long- period comets usually come from the Oort Cloud. Why do comets orbit the Sun? As they fly, comets are pulled toward the Sun because of its powerful gravity. But instead of crashing into the Sun, comets usually curve around it. Their speed propels them back out to distant places in the solar system. Comet Type Period (years) Year of next pass around the Sun Halley's short-period 75 2061 Swift-Tuttle short-period 133 2126 Hale-Bopp long-period 2,530 4527 Hyakutake long-period 17,000-70,000 72,000+

彗星绕太阳运行一圈的时间叫做周期。 短周期彗星绕太阳公转的周期为200年或更短。 它们来自柯伊伯带。 长周期彗星通常来自奥尔特云。 为什么彗星绕太阳运行? 当彗星飞行时，由于太阳强大的引力，它们被拉向太阳。 但彗星通常不会撞向太阳，而是绕着太阳旋转。 它们的速度将它们推回到太阳系的遥远地方。 彗星类型周期(年)下一次绕太阳公转的年份哈雷星短周期75 2061斯威夫特-塔特尔短周期133 2126海尔-波普长周期2530 4527百武长周期17000 - 70000 72000 +

Parts of a Comet What happens when a comet comes close to the Sun? To answer this question, it helps to know the parts of a comet. The main part is the nucleus, which is made up of rock, dust, and ice. The nucleus may be 1 to 40 kilometers (0.6 to 25 mi.) across. When a comet nears the Sun, the intense heat melts some of the ice and burns off tiny bits of the rock and dust. The water vapor and burning bits combine to form an atmosphere called a coma (KO-muh). Even closer to the Sun, the comet develops a tail— a trail of dust and gas. The tail always points away from the Sun. This is due to solar wind, a nonstop flow of particles speeding away from the Sun.

彗星的部分当彗星靠近太阳时会发生什么? 要回答这个问题，了解彗星的各个部分是有帮助的。 主要部分是核，由岩石、尘埃和冰组成。 原子核直径可达1至40公里(0.6至25英里)。 当彗星靠近太阳时，强烈的热量会融化一些冰，燃烧掉微小的岩石和尘埃。 水蒸气和燃烧的碎片结合在一起形成了一种叫做昏迷(KO-muh)的大气。 在离太阳更近的地方，彗星会形成一条彗尾——一条由尘埃和气体组成的轨迹。 彗尾总是指向远离太阳的方向。 这是太阳风造成的，太阳风是一种不间断的粒子流，它加速远离太阳。

It's a Comet's Life Each time a comet nears the Sun, it loses some of its ice and dust. Once all the ice is gone, the comet becomes more like an asteroid. Without the ice to hold it together, it may break into smaller pieces. Some comets meet a more dramatic end. They may get pulled into the gravity of a planet and burn up in its atmosphere. Others may survive to impact the surface. Still other comets are completely destroyed when they travel too close to the Sun. Life Cycle of a Comet 1. A comet begins one of many orbits around the Sun. 2. As the comet nears the Sun, its ice begins to melt, creating the tail. 3. The comet's tail grows longer as it nears the Sun. 4. Due to solar wind, the comet's tail always faces away from the Sun. 5. The comet loses its tail as it moves away from the Sun.

彗星的生命每当彗星靠近太阳时，它就会失去一些冰和尘埃。 一旦所有的冰都消失了，彗星就变得更像一颗小行星。 如果没有冰把它固定在一起，它可能会碎成更小的碎片。 有些彗星的结局更为戏剧性。 它们可能会被行星引力吸引，在大气层中燃烧殆尽。 其他的可能会存活下来撞击地表。 还有一些彗星在离太阳太近时被完全摧毁。 彗星的生命周期一颗彗星开始了围绕太阳的众多轨道之一。 2. 当彗星靠近太阳时，它的冰开始融化，形成了彗尾。 3.彗星越靠近太阳，彗尾越长。 4. 由于太阳风的作用，彗星的尾巴总是背对着太阳。 5. 彗星在远离太阳时失去了尾巴。

Famous Comets In 1994, astronomers observed a comet's doom— and power! Comet Shoemaker-Levy 9 was in close orbit around Jupiter. That July, it began to break up. Pieces crashed into the massive planet. The impacts formed dark spots on the planet's surface. Comet Hale-Bopp was a bright spot in Earth's skies in 1997. Its orbit takes over 2,500 years. The last people who saw it may have been ancient Egyptians! But the real comet superstar is Halley's Comet. It is well known because about every 75 years, right on schedule, it streaks past Earth.

1994年，天文学家观测到了一颗彗星的毁灭和力量!舒梅克-列维9号彗星在木星附近的轨道上运行。 那年7月，它开始解体。 碎片撞向这颗巨大的行星。 撞击在火星表面形成了黑点。 海尔波普彗星是1997年地球天空中的一个亮点。 它的运行周期超过2500年。 最后一个看到它的人可能是古埃及人!但真正的彗星巨星是哈雷彗星。 它之所以为人所知，是因为大约每隔75年，它就会准时经过地球。