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  • General

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  • Stars （Gr 4 - 5）

    Lesson Objectives
    ::经验教训目标

    • Define constellation.
      ::定义星座 。
    • Use light-years as a unit of distance.
      ::使用光年作为距离单位。

    Lesson Vocabulary
    ::词汇表课程

    • constellation
      ::星座星座
    • star
      ::恒星星

    Introduction
    ::导言

    When you look at the sky on a clear night, you can see hundreds of stars. A  star  is a giant ball of glowing gas. Stars are very, very hot. Most of these stars are like our Sun. Some are smaller than our Sun, and some are much larger. Our own star looks large, but only because it is close. Other stars are so far away that they only look like single points, even through a telescope.
    ::当你在一个晴朗的夜晚看着天空时,你可以看到数百颗恒星。恒星是一个发光气体的巨型球。恒星非常、非常热。这些恒星大多与太阳一样。有些比太阳小,有些则大得多。我们自己的恒星看起来很大,但只是因为它很接近。其他恒星距离太远,只能像单点,即使通过望远镜。

    Constellations
    ::星座星座

    The stars that make up a constellation appear close to each other. In reality, they may be very far from one another. Historically, constellations were important to people. Many of these constellations are named from figures in Greek mythology. Back then, people spent a lot of time outdoors at night, like shepherds. They named them and told stories about them.  Figure    shows one of the most known constellations. The ancient Greeks thought this group of stars looked like a hunter. They named it Orion, after a great hunter in Greek mythology.
    ::组成星座的恒星彼此相近。 事实上, 它们可能彼此相距很远。 从历史上看, 星座对人很重要。 许多星座都是根据希腊神话中的数字命名的。 当时, 人们在夜里花了很多时间在户外, 像牧羊人一样。 他们给它们命名并讲述了有关它们的故事。 图显示了最著名的星座之一。 古希腊人认为这组恒星是猎人。 他们把它命名为猎人, 以希腊神话中伟大的猎人命名。

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    Orion has three stars that make up his belt. Orion's belt is fairly easy to see in the night sky.
    ::猎户座有三颗星星组成他的腰带 猎户座的腰带在夜空中很容易看到

    The constellations look the same night after night. The patterns of the stars never change. They always keep their shape. They do move each night across the sky. They move because Earth is spinning on its axis. The constellations also move with the seasons. This is because Earth revolves around the Sun. Some constellations are up only in the winter and others in the summer. For example, Orion is high up in the winter sky. In the summer, it's only up in the early morning. 
    ::星座每晚都一样。 恒星的形态永远不会改变。 它们总是保持形状。 它们每晚都在天空中移动。 它们因为地球在轴上旋转而移动。 星座也随着季节而移动。 这是因为地球围绕太阳旋转。 有些星座只在冬天升起, 另一些星座在夏天升起。 例如, 猎户座在冬空中高高。 夏天, 它只在清晨升起 。

    Lifetimes of Stars
    ::恒星寿命

    We could say that stars are born, change over time, and eventually die. Most stars change in size, color, and class at least once during their lifetime.
    ::我们可以说恒星诞生,随着时间变化而变化,最终死亡。 大多数恒星在其一生中至少一次改变其大小、颜色和等级。

    Formation of Stars
    ::恒星形成

    Stars are born in clouds of gas and dust called nebulas. Our Sun and solar system formed out of a nebula. A nebula is shown in  Figure   . In  Figure   , the fuzzy area beneath the central three stars contains the Orion nebula.
    ::恒星诞生于气体和尘埃云中,称为星云。我们的太阳和太阳系由星云形成。图中显示星云。图中,中三颗恒星下的模糊区域含有猎户座星云。

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    Stars form in a nebula like this one in Orion's sword.
    ::星系形成于星云中 就像这个星云形成于猎户座的剑中

    Stars form because of the force of gravity. Gravity is the attractive force that pulls the dust and gas together. The gas and dust becomes denser. As a result, the pressure and the temperature increase. When the temperature of the center becomes hot enough the star produces its own energy. This process is called nuclear fusion. Once this happens, the ball of gas become a star! 
    ::恒星因重力而形成。 重力是将灰尘和气体凝聚在一起的引力。 气体和尘埃会变稠。 结果, 压力和温度会升高。 当中心温度变得足够热时, 恒星会产生自己的能量。 这个过程被称为核聚变。 一旦发生这种情况, 气体球就会成为恒星 !

    Measuring Star Distances
    ::测量恒星距离

    Astronomers use light years as the unit to describe distances in space. Remember that a light year is the distance light travels in one year.
    ::天文学家使用光年作为描述空间距离的单位。 记住光年是一年中的距离光程。

    How do astronomers measure the distance to stars? For stars that are close to us, they measure shifts in their position over time. This is called parallax. For distant stars, they use the stars' brightness. For example, if a star is like the Sun, it should be about as bright as the Sun. They then figure out the star's distance from Earth by measuring how much less bright it is than expected.
    ::天文学家如何测量恒星与恒星的距离?对于接近我们的恒星,它们测量其位置随时间而变化。这被称为准星。对于遥远的恒星,它们使用恒星的亮度。例如,如果一颗恒星与太阳一样亮,那么它应该与太阳一样亮。然后,它们通过测量比预期的亮度少得多的亮度来了解恒星与地球的距离。

    Lesson Summary
    ::经验教训摘要

    • Constellations are groups of stars that make a shape in the night sky. They may not be close together.
      ::星座是由在夜空中形成形状的恒星组成的群星。星座可能不相近。
    • Star distances can be measured in a number of creative ways.
      ::可以通过若干创造性的方式测量星际距离。

    Lesson Review Questions
    ::经验回顾问题

    Recall
    ::回顾

    1. What is a constellation?
    ::1. 什么是星座?

    2. Why does the Sun (a star) seem bigger than other stars?
    ::2. 为什么太阳(一颗恒星)看起来比其他恒星大?

    Apply Concepts
    ::应用概念

    3. Where are the stars in a constellation located relative to each other? Are they always near each other? Are they always far from each other?
    ::3. 星座中的恒星彼此相邻的位置在哪里?它们是否总是彼此相邻?它们是否总是彼此相距遥远?

    Think Critically
    ::仔细仔细思考

    4. How are stars formed? 
    ::4. 恒星是如何形成的?

    5. How do astronomers know how stars form? What evidence do they have?
    ::5. 天文学家如何知道恒星的形成?他们有什么证据?