📚 Earth and Space: IB & CIE Science Revision | 地球与太空：IB与CIE科学考点精讲
This guide covers key concepts for Earth and Space Science topics commonly assessed in IB MYP and CIE IGCSE Science. From the structure of the Solar System to the life cycle of stars, each section combines essential theory with clear explanations to help you master the content.
本指南涵盖IB MYP与CIE IGCSE科学中常考的地球与太空科学核心概念。从太阳系的结构到恒星的生命周期，每个小节都将重要理论与清晰解释相结合，帮助你彻底掌握这些内容。
1. The Solar System | 太阳系
The Solar System consists of the Sun, eight planets, dwarf planets, moons, asteroids, and comets. The inner planets (Mercury, Venus, Earth, Mars) are rocky and small; the outer planets (Jupiter, Saturn, Uranus, Neptune) are gas giants or ice giants, much larger and composed mainly of hydrogen and helium.
太阳系由太阳、八大行星、矮行星、卫星、小行星和彗星组成。内行星（水星、金星、地球、火星）为岩石质且体积较小；外行星（木星、土星、天王星、海王星）为气态巨行星或冰巨行星，体积大得多，主要由氢和氦组成。
All planets orbit the Sun in elliptical paths due to gravitational attraction. The Sun contains 99.86% of the Solar System’s mass and produces energy through nuclear fusion of hydrogen into helium.
所有行星因引力作用沿椭圆轨道绕太阳运行。太阳占太阳系总质量的99.86%，并通过氢聚变为氦的核反应释放能量。
2. Earth’s Rotation and Revolution | 地球的自转与公转
Earth rotates on its axis once every 24 hours, causing day and night. The side facing the Sun experiences daylight, while the opposite side is in darkness.
地球每24小时绕地轴自转一周，形成昼夜交替。面向太阳的一面为白昼，背向太阳的一面则处于黑夜。
Earth revolves around the Sun once every 365.25 days, which defines one year. Its orbit is slightly elliptical, so the distance from the Sun changes slightly during the year, but this does not cause the seasons.
地球每365.25天绕太阳公转一周，定义为一个回归年。其轨道略呈椭圆形，因此日地距离在一年中有微小变化，但这并非四季的成因。
3. Why We Have Seasons | 四季的成因
The seasons are caused by the tilt of Earth’s axis (about 23.5°) relative to its orbital plane. When the Northern Hemisphere tilts toward the Sun, it experiences summer with longer days and more direct sunlight; the Southern Hemisphere has winter at the same time.
四季是由地轴相对于公转平面约23.5°的倾斜引起的。当北半球向太阳倾斜时，日照时间长且太阳高度角更大，为夏季；此时南半球则为冬季。
During the solstices (around June 21 and December 21), one hemisphere receives maximum sunlight. During the equinoxes (around March 21 and September 23), both hemispheres receive roughly equal sunlight, resulting in spring and autumn.
在至日（约6月21日和12月21日）前后，一个半球获得最大太阳辐射。在分日（约3月21日和9月23日）时，两半球日照大致相等，形成春季和秋季。
4. Phases of the Moon | 月相
The Moon does not produce its own light; we see it because it reflects sunlight. As the Moon orbits Earth, the portion of its illuminated side visible from Earth changes, producing the phases: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, and waning crescent.
月球本身不发光，我们看见它是因其反射太阳光。当月球绕地球运行时，从地球看到的亮面比例随位置改变，形成了新月、蛾眉月、上弦月、盈凸月、满月、亏凸月、下弦月和残月等月相。
The cycle from one new moon to the next takes about 29.5 days, known as a synodic month. The phases align predictably with the relative positions of the Sun, Earth, and Moon.
从一个新月到下一个新月约需29.5天，称为朔望月。月相出现的规律取决于日、地、月三者的相对位置。
5. Tides and Their Causes | 潮汐及其成因
Tides are the periodic rise and fall of sea levels caused mainly by the gravitational pull of the Moon and, to a lesser extent, the Sun. The Moon’s gravity pulls water toward it, creating a bulge on the side facing the Moon and a secondary bulge on the opposite side due to inertia.
潮汐是主要由月球（其次为太阳）的引力引起的海平面周期性涨落。月球引力将海水拉向月球方向，在地球面向月球的一侧形成隆起，同时因惯性作用在背向月球的一侧也形成隆起。
Spring tides occur when the Sun, Earth, and Moon align (new and full moon), producing extra-high tides. Neap tides occur when the Sun and Moon are at right angles relative to Earth (first and last quarter), producing weaker tides.
当日、地、月排成一线（新月和满月）时发生大潮，潮差最大；当太阳和月球与地球成直角（上弦月和下弦月）时发生小潮，潮差最小。
6. Solar and Lunar Eclipses | 日食与月食
A solar eclipse happens when the Moon passes between the Sun and Earth, casting a shadow on Earth. In a total solar eclipse, the Moon fully covers the Sun. A partial eclipse occurs when only part of the Sun is blocked.
月球经过日地之间并将影子投到地球上时，发生日食。日全食时月球完全遮住太阳；日偏食时仅部分太阳被遮挡。
A lunar eclipse occurs when Earth lies between the Sun and Moon, and the Moon passes through Earth’s shadow. During a total lunar eclipse, the Moon can appear red due to scattering of sunlight by Earth’s atmosphere.
当地球位于日月之间，月球进入地影时发生月食。月全食时，由于地球大气对日光的散射，月球可能呈现红色。
Eclipses do not occur every month because the Moon’s orbit is tilted about 5° relative to Earth’s orbital plane, so the three bodies rarely align perfectly.
由于月球轨道相对于地球公转平面倾斜约5°，日、地、月三者很少完美对齐，因此并非每月都会发生食。
7. Stars and Galaxies | 恒星与星系
A star is a massive, luminous ball of plasma held together by gravity. Its energy comes from nuclear fusion in its core, where hydrogen is converted into helium. The Sun is a typical main-sequence star.
恒星是由引力约束在一起的巨大发光等离子体球，其能量来源于核心的核聚变，将氢转变为氦。太阳便是一颗典型的主序星。
A galaxy is a vast collection of stars, gas, dust, and dark matter. Our Solar System belongs to the Milky Way, a spiral galaxy containing hundreds of billions of stars. Other galaxy types include elliptical and irregular galaxies.
星系是由恒星、气体、尘埃和暗物质组成的庞大集合。太阳系位于银河系内，这是一个包含数千亿颗恒星的旋涡星系。其它星系类型还有椭圆星系和不规则星系。
8. Life Cycle of Stars | 恒星的生命周期
Stars form from nebulae – clouds of dust and gas – that collapse under gravity. A protostar forms, and when its core temperature becomes high enough for hydrogen fusion, it becomes a main-sequence star. Low-mass stars like the Sun eventually become red giants, then shed their outer layers to form planetary nebulae, leaving behind a white dwarf.
恒星起源于星云（尘埃和气体云），在引力作用下坍缩。原恒星形成后，若核心温度足以引发氢聚变，便成为主序星。像太阳这样的低质量恒星最终会变为红巨星，抛掉外层形成行星状星云，中心留下一颗白矮星。
High-mass stars evolve through red supergiant stages and can end their lives in a supernova explosion. The core remnant may become a neutron star or, if massive enough, a black hole. These processes spread heavy elements into space.
大质量恒星演化经过红超巨星阶段，最终以超新星爆发结束生命。核心残骸可能变为中子星，若质量足够大则形成黑洞。这些过程将重元素散布到太空中。
9. The Expanding Universe and the Big Bang | 膨胀的宇宙与大爆炸
Observations show that galaxies are moving away from each other. The redshift of light from distant galaxies indicates that the Universe is expanding. This expansion supports the Big Bang theory, which states that the Universe began from an extremely hot and dense point about 13.8 billion years ago.
观测表明星系正在相互远离。遥远星系光谱的红移证明宇宙正在膨胀。这一膨胀支持了大爆炸理论，该理论认为宇宙约138亿年前起源于一个极热极密的奇点。
Cosmic microwave background radiation is the remnant heat from the Big Bang and provides strong evidence for the theory. The Universe has been cooling and expanding ever since.
宇宙微波背景辐射是大爆炸后遗留的热辐射，为理论提供了有力证据。自此以后，宇宙一直在冷却和膨胀。
10. Observing the Universe | 观测宇宙
Astronomers use telescopes that detect different regions of the electromagnetic spectrum. Optical telescopes observe visible light, while radio telescopes detect radio waves. Space telescopes like the Hubble Space Telescope can observe ultraviolet and infrared light without atmospheric interference.
天文学家使用能探测电磁波谱不同波段的天文望远镜。光学望远镜观测可见光，射电望远镜捕捉射电波。像哈勃空间望远镜这样的空间望远镜可避开大气干扰，观测紫外和红外光。
Satellites and space probes, including those sent to Mars and the outer planets, provide direct data about our Solar System. Sample-return missions help scientists study extraterrestrial materials on Earth.
卫星和空间探测器（包括前往火星和外行星的探测器）提供了关于太阳系的直接数据。样品返回任务使科学家能够在地球上研究地外物质。
11. Key Equations and Units | 关键方程与单位
Orbital speed = 2π × orbital radius / orbital period (v = 2πr / T)
轨道速率 = 2π × 轨道半径 / 轨道周期 (v = 2πr / T)
Distances in space are measured in astronomical units (AU) within the Solar System, light-years (ly) for interstellar distances, and parsecs (pc) for larger scales. 1 AU is the average Earth-Sun distance (∼1.5 × 10⁸ km).
太空中的距离在太阳系内使用天文单位（AU），恒星间距离用光年（ly），更大尺度用秒差距（pc）。1 AU为日地平均距离，约1.5 × 10⁸ 千米。
12. Common Exam Pitfalls | 常见考试误区
Avoid confusing the Moon’s orbital period with its phase cycle. The Moon takes about 27.3 days to orbit Earth (sidereal month), but the synodic month (phase cycle) takes 29.5 days because Earth is also moving around the Sun.
不要混淆月球的公转周期与月相周期。月球绕地球公转一周约需27.3天（恒星月），但因地球本身也在绕日公转，朔望月（月相周期）需29.5天。
Do not think that seasons are caused by Earth’s varying distance from the Sun. The tilt of the axis is the correct explanation. Also, remember that the same side of the Moon always faces Earth because its rotational period equals its orbital period (tidal locking).
切勿认为四季是由地球距太阳远近变化引起的，地轴倾斜才是正确解释。此外，需牢记月球始终以同一面朝向地球，因为其自转周期与公转周期相等（潮汐锁定）。
When interpreting spectra, a redshift indicates motion away from the observer, while a blueshift indicates motion toward the observer. Greater shift means higher relative speed.
在分析光谱时，红移表示远离观测者运动，蓝移表示靠近观测者运动。移动量越大，相对速度越高。
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