AQA A-Level Physics: Astrophysics – Key Concepts and Exam Tips | AQA A-Level 物理：天体物理考点精讲

📚 AQA A-Level Physics: Astrophysics – Key Concepts and Exam Tips | AQA A-Level 物理：天体物理考点精讲

The Astrophysics option in AQA A-Level Physics explores telescopes, stellar physics, cosmology and distance measurement. This guide distils the essential concepts, equations and examination techniques to help you master this fascinating topic.

AQA A-Level 物理的天体物理选修模块涵盖望远镜、恒星物理、宇宙学与距离测量。本指南提炼核心概念、公式与应试技巧，助你掌握这一迷人领域。

1. Telescopes and Collecting Power | 望远镜与集光力

Optical telescopes come in two main designs: refractors use lenses, while reflectors use mirrors. Reflectors are preferred for large astronomical telescopes because mirrors can be made larger and do not suffer from chromatic aberration. The most important property is collecting power, proportional to the area of the primary mirror or lens. A telescope with twice the diameter of another collects four times as much light.

光学望远镜主要有两种设计：折射式用透镜，反射式用镜面。大型天文望远镜偏向反射式，因镜面可做得更大且无色差。最重要的特性是集光力，正比于主镜或透镜的面积。因此直径加倍意味着收集四倍光通量。

Collecting Power ∝ D²

The angular magnification produced by a telescope is given by M = fₒ / fₑ, where fₒ is the objective focal length and fₑ is the eyepiece focal length. However, in astrophysics, light-gathering power and angular resolution are often far more critical than magnification.

望远镜的角放大率由 M = fₒ / fₑ 给出，其中 fₒ 为物镜焦距，fₑ 为目镜焦距。但在天体物理中，集光力和角分辨率往往比放大率更为重要。

2. Angular Resolution and Radio Telescopes | 角分辨率与射电望远镜

The angular resolution of a telescope is its ability to separate two close point sources. For a diffraction-limited instrument observing at wavelength λ with a primary aperture of diameter D, the minimum angular separation θ is approximately λ / D (radians). Because radio wavelengths are orders of magnitude longer than optical wavelengths, a single radio dish has much worse resolution than an optical telescope of the same diameter.

角分辨率指望远镜区分两个邻近点源的能力。对于衍射极限仪器，观测波长 λ、主镜口径 D 时，最小角分离 θ ≈ λ / D（弧度）。由于射电波长比光学波长长数个量级，同等口径下单一射电望远镜的分辨率远差于光学望远镜。

θ ≈ λ / D

To overcome this, astronomers use radio interferometry, combining signals from multiple dishes separated by large distances. The effective baseline can be kilometres, yielding arcsecond or even milliarcsecond resolution. Examples include the e-MERLIN array and the Event Horizon Telescope.

为弥补不足，天文学家用射电干涉技术，将相隔很远的多面天线信号合并，等效基线可达数千米，可获得角秒甚至毫角秒级的分辨率。实例包括 e-MERLIN 阵列和事件视界望远镜。

3. Stellar Quantities: Apparent Magnitude and Absolute Magnitude | 视星等与绝对星等

The magnitude scale is logarithmic: a difference of 5 magnitudes corresponds to a brightness ratio of exactly 100. The apparent magnitude m measures how bright a star looks from Earth, while the absolute magnitude M

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