📚 GCSE WJEC Science: Earth and Space Key Points | GCSE WJEC 科学：地球与太空 考点精讲
This revision guide covers the essential concepts for the Earth and Space topic in GCSE WJEC Science. You will learn about the Solar System, gravity, orbits, stellar life cycles, the expanding Universe, and evidence for the Big Bang. Each section is presented in English and Chinese to help you master the key points.
本文梳理了 GCSE WJEC 科学中地球与太空专题的核心考点。你将学习太阳系、引力、轨道、恒星生命周期、宇宙膨胀及大爆炸证据。每个小节都采用中英双语对照讲解，帮助你牢固掌握重点。
1. The Solar System | 太阳系
The Solar System consists of the Sun and all the objects that orbit it, including planets, dwarf planets, moons, asteroids, and comets.
太阳系由太阳和所有围绕它运行的天体组成，包括行星、矮行星、卫星、小行星和彗星。
The eight planets in order from the Sun are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The first four are inner rocky planets; the outer four are gas giants (Jupiter and Saturn) and ice giants (Uranus and Neptune).
八大行星距太阳由近到远的顺序是：水星、金星、地球、火星、木星、土星、天王星、海王星。前四颗为内层岩石行星，外四颗为气态巨行星（木星和土星）与冰态巨行星（天王星和海王星）。
The asteroid belt, a region containing many small rocky bodies, lies between Mars and Jupiter.
小行星带位于火星与木星之间，该区域包含了大量小型岩石天体。
2. Geocentric vs Heliocentric Models | 地心说与日心说
Historically, the geocentric model placed Earth at the centre of the Universe, with planets and the Sun orbiting it. This was later replaced by the heliocentric model, which places the Sun at the centre.
历史上，地心说将地球置于宇宙的中心，行星和太阳绕地球运行。后来这一模型被日心说取代，日心说认为太阳是宇宙的中心。
Nicolaus Copernicus proposed the heliocentric model, and Galileo Galilei’s telescopic observations, such as the moons of Jupiter, provided strong evidence against the geocentric view.
尼古拉·哥白尼提出了日心说，伽利略使用望远镜观测到的木星卫星等现象为反对地心说提供了有力证据。
3. Gravity and Orbits | 重力与轨道
Gravity is a force of attraction between all masses. The greater the mass of an object, the stronger its gravitational pull. Newton’s law of gravitation states: F = G m₁ m₂ / r², where G is the gravitational constant, m₁ and m₂ are the masses, and r is the distance between their centres.
重力是所有具有质量的物体之间存在的吸引力。物体的质量越大，引力越强。牛顿万有引力定律表示为：F = G m₁ m₂ / r²，其中 G 是万有引力常数，m₁ 与 m₂ 是两个物体的质量，r 是它们中心之间的距离。
In orbital motion, gravity provides the centripetal force needed to keep a body moving in a curved path around another. For a circular orbit, the orbital speed can be expressed as v = √(GM / r), where M is the mass of the central body and r is the orbital radius.
在轨道运动中，重力提供了使物体绕另一天体做曲线运动所需的向心力。对于圆轨道，轨道速度可表示为 v = √(GM / r)，其中 M 是中心天体的质量，r 是轨道半径。
4. Orbital Motion and Satellites | 轨道运动与卫星
A satellite is any object that orbits a planet or star. Natural satellites include moons; artificial satellites are man-made and serve purposes such as communication, weather monitoring, GPS, and scientific research.
卫星是围绕行星或恒星运行的任何天体。天然卫星包括月球；人造卫星由人类制造，用于通信、气象监测、全球定位系统以及科学研究等目的。
Satellites in low Earth orbit (LEO) have shorter orbital periods and travel faster than those in geostationary orbit. A geostationary satellite has a period of exactly 24 hours and appears fixed above a point on Earth’s equator.
近地轨道卫星的轨道周期较短且速度较快。而地球静止轨道卫星的周期正好是 24 小时，看起来固定在赤道上空的某个点上不动。
5. The Life Cycle of Stars | 恒星的生命周期
A star begins its life as a cloud of gas and dust called a nebula. Under gravity, the nebula collapses to form a protostar. When the core temperature reaches about 15 million °C, nuclear fusion of hydrogen into helium starts, and a main sequence star is born.
恒星的生命始于一团称为星云的气体和尘埃。在引力作用下，星云坍缩形成原恒星。当核心温度达到约 1500 万 °C 时，氢聚变为氦的核反应启动，一颗主序星就诞生了。
The Sun is currently a main sequence star. In the future, when the hydrogen in its core is exhausted, it will expand into a red giant, shed its outer layers as a planetary nebula, and leave behind a white dwarf.
太阳目前是一颗主序星。当核心的氢耗尽后，它将膨胀为红巨星，然后抛射外层形成行星状星云，最终留下一颗白矮星。
For stars much more massive than the Sun, the red giant stage becomes a red supergiant, which then undergoes a supernova explosion. The remnant can be a neutron star or, if massive enough, a black hole.
对于质量远大于太阳的恒星，红巨星阶段后会成为红超巨星，随后发生超新星爆炸。爆炸残骸可能是中子星，如果质量足够大，则会形成黑洞。
6. The Sun as a Star | 太阳作为恒星
The Sun is a medium-sized main sequence star composed mainly of hydrogen and helium. It generates energy through nuclear fusion, converting about 4 million tonnes of mass into energy every second according to E = mc².
太阳是一颗中等大小的主序星，主要成分是氢和氦。它通过核聚变产生能量，根据质能方程 E = mc²，每秒约有 400 万吨的质量转化为能量。
The Sun remains stable because of a balance between the inward pull of gravity and the outward thermal pressure produced by fusion reactions. This state is called hydrostatic equilibrium.
太阳保持稳定，是因为向内的引力与聚变产生的向外热压力相互平衡。这种状态称为流体静力平衡。
7. The Expanding Universe and Redshift | 宇宙膨胀与红移
Observations show that light from distant galaxies is shifted towards the red end of the spectrum. This redshift indicates that galaxies are moving away from us, and the further away a galaxy is, the faster it recedes (Hubble’s Law).
观测表明，来自遥远星系的光谱向红端移动，即发生红移。这说明星系正在远离我们，并且星系越遥远，远离的速度越快（哈勃定律）。
Redshift occurs because the wavelength of light is stretched as the source moves away, similar to the Doppler effect for sound waves. This provides strong evidence that the Universe is expanding.
红移的产生是因为光源远离时，光的波长被拉长，这与声波的多普勒效应类似。这为宇宙正在膨胀提供了强有力的证据。
8. The Big Bang Theory | 大爆炸理论
The Big Bang theory states that the Universe began approximately 13.8 billion years ago from an extremely hot and dense singularity. It has been expanding and cooling ever since.
大爆炸理论认为宇宙大约在 138 亿年前从一个极其炽热和致密的奇点开始，此后一直在膨胀和冷却。
All matter, energy, space, and time were created at that instant. The initial rapid expansion is known as inflation, and the ongoing expansion is confirmed by the observed redshift of galaxies.
所有的物质、能量、空间和时间都是在那一刻创造的。最初的急剧膨胀称为暴胀，而目前宇宙的持续膨胀已通过观测到的星系红移得到证实。
9. Cosmic Microwave Background Radiation (CMBR) | 宇宙微波背景辐射
CMBR is a faint radiation that fills the entire Universe uniformly in all directions. Its temperature is approximately 2.7 K (-270.45 °C), and it is considered the afterglow of the Big Bang, released about 380,000 years after the Universe began.
CMBR 是一种充满宇宙各个方向的微弱辐射。其温度约为 2.7 K（-270.45 °C），被认为是大爆炸的余辉，在宇宙开始后约 38 万年时释放出来。
The near-perfect uniformity of CMBR supports the idea that the Universe was once in a hot, dense state and has expanded greatly over time.
CMBR 近乎完美的均匀性支持了宇宙早期处于高温致密状态并随时间发生巨大膨胀的观点。
10. Evidence for the Big Bang | 大爆炸的证据
The two main pieces of evidence for the Big Bang are the redshift of distant galaxies and the existence of the cosmic microwave background radiation. Together they firmly support the theory that the Universe began from a single point and has expanded.
支持大爆炸理论的两项主要证据是遥远星系的红移与宇宙微波背景辐射的存在。两者共同有力地支撑了宇宙从一点开始并不断膨胀的理论。
Redshift demonstrates that galaxies are moving apart, while CMBR exactly matches predictions of a hot, dense early Universe. No other widely accepted theory explains both observations so successfully.
红移表明星系正在彼此远离，而 CMBR 则完全符合对早期高温致密宇宙的预测。目前没有其他被广泛接受的理论能如此圆满地解释这两项观测。
11. Dark Matter and Dark Energy | 暗物质与暗能量
Dark matter is a form of matter that does not emit, absorb, or reflect light, making it invisible. Its presence is inferred from gravitational effects on visible matter and the rotation curves of galaxies.
暗物质是一种不发射、吸收或反射光的物质，因此无法直接看见。人们通过它对可见物质的引力作用以及星系的旋转曲线推断出它的存在。
Dark energy is a mysterious force that is causing the expansion of the Universe to accelerate. It is estimated to make up about 68% of the total energy density of the Universe.
暗能量是一种导致宇宙膨胀加速的神秘力量。据估计，暗能量约占宇宙总能量密度的 68%。
12. The Future of the Universe | 宇宙的未来
Current observations indicate that the expansion of the Universe is accelerating due to dark energy. Possible ultimate fates include the ‘Big Freeze’ (continued expansion and cooling) or the ‘Big Rip’, depending on the true nature of dark energy.
目前的观测表明，由于暗能量的作用，宇宙膨胀正在加速。宇宙可能的最终命运包括“大冻结”（持续膨胀并冷却）或“大撕裂”，具体取决于暗能量的真实性质。
If gravity were to overpower expansion, a ‘Big Crunch’ could occur, but current data favour a Universe that expands forever. The ultimate fate remains an active area of research.
如果引力战胜了膨胀，可能会发生“大坍缩”，但当前的数据支持宇宙将永远膨胀下去。宇宙的最终命运仍是一个活跃的研究领域。
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