📚 Earth and Space: Key Concepts for IB and Edexcel Science | 地球与太空：IB与Edexcel科学考点精讲
The study of Earth and space unites physics, chemistry, and geography to explain our planet’s place in the cosmos. Whether you are following the IB Middle Years Programme or Edexcel GCSE Science, mastering key ideas about orbits, seasons, and celestial phenomena is essential. This revision guide breaks down the most important concepts, equations, and observational skills you need to excel.
地球与太空的学习融合了物理学、化学和地理学，用以解释我们的星球在宇宙中的位置。无论你是在学习IB中学项目还是Edexcel GCSE科学，掌握轨道、季节和天体现象等关键概念都至关重要。本文梳理了你需要掌握的最重要的概念、方程式和观测技能。
1. The Solar System and Celestial Bodies | 太阳系与天体
Our Solar System consists of one star, the Sun, and all the objects bound by its gravity. These include eight planets, their moons, dwarf planets like Pluto, asteroids, and comets. The inner planets (Mercury, Venus, Earth, Mars) are rocky and small, while the outer planets (Jupiter, Saturn, Uranus, Neptune) are gas giants with many moons and ring systems.
我们的太阳系由一颗恒星——太阳以及所有被其引力束缚的天体组成。这包括八颗行星、它们的卫星、像冥王星这样的矮行星、小行星和彗星。内行星（水星、金星、地球、火星）体积小、由岩石构成，而外行星（木星、土星、天王星、海王星）是拥有许多卫星和环系统的气态巨行星。
The asteroid belt lies between Mars and Jupiter, containing rocky remnants from the early Solar System. Comets, made of ice and dust, originate mainly from the Kuiper Belt and Oort Cloud, developing bright tails when they approach the Sun.
小行星带位于火星和木星之间，含有早期太阳系遗留下来的岩石碎块。由冰和尘埃组成的彗星主要来自柯伊伯带和奥尔特云，当它们接近太阳时会形成明亮的彗尾。
Pluto was reclassified as a dwarf planet in 2006 because it has not cleared its orbital neighbourhood of other objects. This classification helps students understand that scientific definitions evolve with new evidence.
冥王星在2006年被重新分类为矮行星，因为它尚未清除其轨道附近的其他天体。这一分类有助于学生理解科学定义会随着新证据而演变。
A useful mnemonic for the order of planets from the Sun is: “My Very Educated Mother Just Served Us Noodles” (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune).
一个记忆行星距日顺序的口诀是：”My Very Educated Mother Just Served Us Noodles”（水星、金星、地球、火星、木星、土星、天王星、海王星）。
2. Earth’s Rotation and Day-Night Cycle | 地球自转与昼夜交替
Earth rotates on its axis once approximately every 24 hours, causing the daily cycle of day and night. The axis is an imaginary line passing through the North and South Poles, tilted at an angle of about 23.5° relative to the plane of its orbit.
地球每约24小时绕其地轴自转一周，形成了昼夜交替。地轴是一条穿过南北两极的假想线，相对于公转平面倾斜大约23.5°。
The side of Earth facing the Sun experiences daylight, while the opposite side is in darkness. This rotation is also responsible for the apparent movement of the Sun, Moon, and stars across the sky from east to west.
地球面向太阳的一面是白昼，背向的一面则处于黑暗中。这种自转也造成了太阳、月亮和星星在天空中自东向西的视运动。
A full rotation is 360°, and Earth rotates at an angular speed of 15° per hour. This can be used to calculate time differences between longitudes: for every 15° of longitude, there is a one-hour difference in local time.
一整圈自转为360°，地球自转的角速度为每小时15°。这可以用来计算经度之间的时差：每相差15°经度，地方时就相差一小时。
The Coriolis effect, a consequence of Earth’s rotation, deflects moving air and water to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, influencing global wind patterns and ocean currents.
地转偏向力（科里奥利效应）是地球自转的结果，它使运动中的空气和水在北半球向右偏转，在南半球向左偏转，从而影响全球风带和洋流。
3. Earth’s Revolution and Seasons | 地球公转与四季
Earth revolves around the Sun in an elliptical orbit, completing one full revolution in approximately 365.25 days. The combination of this orbit and the axial tilt produces the seasons, not the varying distance from the Sun.
地球沿着椭圆形轨道绕太阳公转，约365.25天完成一圈。公转和地轴倾角共同造就了四季变化，而非距离太阳的远近。
During June, the Northern Hemisphere is tilted toward the Sun, receiving more direct sunlight and longer days, resulting in summer. Meanwhile, the Southern Hemisphere experiences winter. In December, the situation reverses.
六月时，北半球倾向太阳，获得更直接的光照和更长的白昼，形成夏季。此时南半球则是冬季。十二月时这一情况发生反转。
The equinoxes occur around 20 March and 22 September, when neither hemisphere is tilted toward the Sun, and day and night are nearly equal in length worldwide. The solstices mark the longest and shortest days of the year, around 21 June and 21 December.
春分和秋分大约发生在3月20日和9月22日，此刻两个半球均不向太阳倾斜，全球昼夜近乎等长。冬至和夏至则分别是一年中白昼最短和最长的日子，大约在12月21日和6月21日。
The analemma, a figure-eight pattern traced by the Sun’s position in the sky at the same mean solar time throughout the year, illustrates the combined effects of axial tilt and orbital eccentricity. While not always required in exams, it deepens understanding of solar motion.
太阳在全年同一平太阳时下位置所绘出的八字形图案称为“日行迹”（analemma），它展示了地轴倾角和轨道偏心率共同作用的效果。虽然不一定考，但能加深对太阳运动的理解。
4. The Moon’s Phases and Tides | 月相与潮汐
The Moon orbits Earth approximately every 27.3 days (sidereal month), but the cycle of phases—new moon to new moon—takes about 29.5 days (synodic month) because Earth is also moving around the Sun. Phases result from the changing relative positions of the Earth, Moon, and Sun.
月球约每27.3天（恒星月）绕地球一圈，但月相变化周期——从新月到下一次新月——则大约需要29.5天（朔望月），因为地球也在绕日运动。月相产生于地球、月球和太阳三者相对位置的改变。
The main phases in order are: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third quarter, and waning crescent. During a full moon, the Moon is opposite the Sun in the sky, rising as the Sun sets.
月相的主要顺序为：新月、蛾眉月、上弦月、盈凸月、满月、亏凸月、下弦月和残月。满月时，月亮在天空中与太阳相对，随日落而升起。
The gravitational pull of the Moon (and to a lesser extent the Sun) causes ocean tides. Spring tides, with the highest high tides and lowest low tides, occur when the Sun, Earth, and Moon align (during full and new moons). Neap tides, with the smallest tidal range, occur when the Moon and Sun are at right angles relative to Earth (during quarter moons).
月球（以及较小程度上太阳）的引力引起了海洋潮汐。当太阳、地球和月球排成一线（满月和新月）时会出现大潮，潮差最大；而当月球和太阳相对于地球成直角（上弦月、下弦月）时则出现小潮，潮差最小。
Many exam questions ask students to identify the phase given a diagram of Earth-Moon-Sun positions or to predict tide types. Drawing clear diagrams helps avoid confusion.
许多考题会给出一幅地日月位置图，要求学生判断月相或预测潮汐类型。绘制清晰的示意图有助于避免混淆。
5. Eclipses: Solar and Lunar | 日食与月食
An eclipse occurs when one celestial body moves into the shadow of another. A solar eclipse happens when the Moon passes between the Earth and the Sun, casting a shadow on Earth. A lunar eclipse occurs when the Earth passes between the Sun and the Moon, and the Moon enters Earth’s shadow.
当一个天体进入另一个天体的影子时就会发生食。当月球经过地球和太阳之间，在地球上投下阴影时，发生日食。当地球经过太阳和月球之间，月球进入地球的影子时，则发生月食。
Solar eclipses can be total, partial, or annular depending on the alignment and the Moon’s distance from Earth. During a total solar eclipse, the Moon’s umbra reaches Earth’s surface, and the Sun’s corona becomes visible. Viewers must use special eye protection.
日食可分为日全食、日偏食或日环食，取决于太阳、月球和地球的排列以及月球与地球的距离。日全食期间，月球的本影抵达地球表面，日冕变得可见。观测者必须使用专用的护目设备。
Lunar eclipses are safe to view with the naked eye. A total lunar eclipse often turns the Moon a reddish colour due to sunlight refracting through Earth’s atmosphere—commonly called a “blood moon”.
月食用肉眼观看是安全的。月全食常常使月球呈现微红色，因为太阳光穿过地球大气层发生了折射——俗称“血月”。
Eclipses do not happen every month because the Moon’s orbit is tilted about 5° relative to Earth’s orbital plane. The Moon usually passes above or below the Earth-Sun line, and eclipses only occur when the nodes align.
月食或日食并非每月发生，因为月球轨道相对于地球公转平面倾斜了约5°。月球通常会从地球-太阳连线的上方或下方经过，只有在交点对齐时才会发生食。
6. Gravity and Orbits | 引力与轨道
All objects with mass exert a gravitational force. The force between two masses is described by Newton’s law of universal gravitation:
任何有质量的物体都会产生引力。两个质量之间的力由牛顿万有引力定律描述：
F = G m₁ m₂ / r²
where G = 6.674 × 10⁻¹¹ N m² kg⁻² is the gravitational constant, m₁ and m₂ are the masses, and r is the distance between their centres.
其中 G = 6.674×10⁻¹¹ N·m²/kg² 为引力常数，m₁ 和 m₂ 分别为两物体的质量，r 为两者中心间的距离。
An orbit is a balance between the forward motion of a satellite and the gravitational pull of the larger body. The centripetal force required to keep an object in circular motion is provided by gravity, which is why the Moon stays in orbit around Earth and planets stay in orbit around the Sun.
轨道是卫星的向前运动与其绕行较大天体的引力之间的一种平衡。维持圆周运动所需的向心力由引力提供，这就是月球环绕地球、行星环绕太阳运行的原因。
The speed of a satellite in a low Earth orbit is about 7.8 km/s. The orbital period increases with the orbital radius: the International Space Station completes an orbit in about 90 minutes, while a geostationary satellite takes exactly one day.
近地轨道卫星的速度约为 7.8 km/s。轨道半径越大，轨道周期越长：国际空间站约90分钟绕地一圈，而地球同步轨道卫星则正好一天绕一圈。
To calculate orbital velocity for a circular orbit, you can equate centripetal force formula mv²/r to gravitational force GMm/r², giving v = √(GM/r). This shows velocity depends on the mass of the central body, not the satellite.
计算圆形轨道的轨道速度时，可令向心力公式 mv²/r 等于万有引力 GMm/r²，得到 v = √(GM/r)。这表明轨道速度取决于中心天体的质量，而非卫星的质量。
7. The Scale of the Universe and Light Years | 宇宙的尺度与光年
Distances in space are so vast that astronomers use light years, the distance light travels in one year. One light year is approximately 9.46 trillion kilometres (9.46 × 10¹² km).
宇宙空间中的距离极其遥远，天文学家使用光年作为单位，即光在一年中所走的距离。一光年大约是 9.46 万亿公里（9.46×10¹² km）。
Our Milky Way galaxy is about 100,000 light years across and contains over 200 billion stars. The nearest star to the Sun, Proxima Centauri, is 4.24 light years away, meaning its light takes over four years to reach us.
我们的银河系直径约 10 万光年，含有超过 2000 亿颗恒星。离太阳最近的恒星比邻星距离 4.24 光年，这意味着它的光芒需要超过四年才能到达我们。
Using the speed of light c = 3.00 × 10⁸ m/s, we can convert years to metres: distance = speed × time. IB and Edexcel exams may ask students to perform such conversions or compare astronomical distances.
利用光速 c = 3.00×10⁸ m/s，我们可以将年转换为米：距离 = 速度 × 时间。IB和Edexcel考试可能会要求学生进行这类换算，或比较不同的天文距离。
An astronomical unit (AU) is the average Earth-Sun distance, about 150 million km. It is used for measuring distances within the Solar System, while parsecs and light years are used for larger scales.
天文单位（AU）是指地球到太阳的平均距离，约 1.5 亿公里，用于测量太阳系内的距离，而秒差距和光年则用于更大的尺度。
8. Observing the Night Sky | 观测夜空
With the naked eye, we can see planets, bright stars, and constellations. Planets shine with a steady light because they are relatively close and appear as discs, while stars twinkle due to atmospheric turbulence affecting their pinpoint light.
用肉眼我们可以看见行星、亮星和星座。行星的光比较稳定，因为它们相对较近并呈圆面状，而星星会闪烁则是由于大气湍流影响了它们点状的光。
Constellations are patterns of stars as seen from Earth, often named after mythological figures, animals, or objects. The International Astronomical Union recognises 88 constellations, such as Orion, Ursa Major, and Scorpius.
星座是从地球上看到的恒星组合，通常以神话人物、动物或物品命名。国际天文学联合会承认 88 个星座，如猎户座、大熊座和天蝎座。
A star’s brightness as seen from Earth is its apparent magnitude, while absolute magnitude refers to how bright a star would appear at a standard distance of 10 parsecs (32.6 light years). Lower magnitudes correspond to brighter objects.
从地球看到的恒星亮度称为视星等，而绝对星等则指将恒星放在标准距离 10 秒差距（32.6 光年）处时所呈现的亮度。星等越低，天体越亮。
Using a simple telescope or binoculars, you can observe craters on the Moon, the moons of Jupiter, and the rings of Saturn. Understanding how telescopes use lenses or mirrors to gather and focus light is a common exam topic.
使用简单的望远镜或双筒望远镜，你可以观察到月球上的环形山、木星的卫星以及土星的光环。理解望远镜如何利用透镜或反射镜收集和聚焦光线是常见的考点。
9. Space Exploration and Technology | 太空探索与技术
Humans have sent probes to all planets in the Solar System, and rovers like Curiosity and Perseverance are actively studying the surface of Mars. The Voyager 1 and 2 spacecraft, launched in 1977, have now entered interstellar space.
人类已经向太阳系所有行星发射了探测器，像“好奇号”和“毅力号”这样的火星车正在积极研究火星表面。1977 年发射的旅行者 1 号和 2 号探测器现已进入星际空间。
Satellites in Earth orbit provide communication, navigation (GPS), weather monitoring, and Earth observation. Geostationary satellites orbit at about 36,000 km above the equator and stay fixed over one spot on the ground.
环绕地球的卫星提供通信、导航（GPS）、气象监测和地球观测服务。地球静止轨道卫星在赤道上方约 36,000 km 处环绕地球，并固定在地面上方的某个点上。
Telescopes such as the Hubble Space Telescope and the James Webb Space Telescope operate in space to avoid atmospheric distortion and to observe infrared and ultraviolet light that the atmosphere largely blocks. They have revolutionised our understanding of the universe.
哈勃太空望远镜和詹姆斯·韦伯太空望远镜等望远镜在太空中运行，既能避免大气扰动，又能观测被大气层大量遮挡的红外线和紫外线。它们彻底改变了我们对宇宙的认知。
Challenges of space travel include microgravity’s effects on the human body, exposure to cosmic radiation, and the psychological impact of long-duration isolation. Solutions such as spacecraft shielding and exercise regimes are active areas of research.
太空旅行面临的挑战包括微重力对人体的影响、宇宙辐射的暴露以及长期隔离带来的心理冲击。宇宙飞船屏蔽和运动方案等应对措施是当前活跃的研究领域。
10. Climate and the Atmosphere | 气候与大气层
Earth’s atmosphere is a thin layer of gases held by gravity, composed mainly of nitrogen (78%) and oxygen (21%), with traces of argon, carbon dioxide, and water vapour. This mixture supports life and regulates temperature through the greenhouse effect.
地球大气层是一层由引力束缚的薄薄气体层，主要成分为氮气（78%）和氧气（21%），还有微量的氩气、二氧化碳和水蒸气。这层混合气体通过温室效应维持生命和调节温度。
Greenhouse gases like CO₂, methane, and water vapour trap heat in the atmosphere. Human activities such as burning fossil fuels have increased CO₂ levels, enhancing the natural greenhouse effect and causing global warming.
二氧化碳、甲烷和水蒸气等温室气体会在大气中捕获热量。燃烧化石燃料等人类活动提高了二氧化碳浓度，增强了自然温室效应，导致全球变暖。
The ozone layer in the stratosphere absorbs harmful ultraviolet radiation from the Sun. Its thinning due to CFCs was a major environmental issue, but international agreements like the Montreal Protocol have helped in its recovery.
平流层中的臭氧层吸收来自太阳的有害紫外线辐射。氯氟碳化合物（CFCs）造成的臭氧层变薄曾是一个重大环境问题，但《蒙特利尔议定书》等国际协议已帮助其逐步恢复。
The Earth’s climate system includes interactions between the atmosphere, hydrosphere, cryosphere, land surface, and biosphere. Understanding these connections is vital not only for science exams but for informed global citizenship.
地球气候系统包括大气圈、水圈、冰冻圈、地表和生物圈之间的相互作用。理解这些联系不仅对科学考试至关重要，对成为有见识的世界公民也必不可少。
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