什么是光年？
What is a light-year?
光年是距离单位，指光在真空中一年走过的距离，约为9.46万亿公里。因为宇宙极其广阔，用公里表示天体距离会数字太大，所以天文学家改用光年。注意：光年说的是距离，不是时间。
A light-year is a unit of distance, the length light travels in vacuum in one year, about 9.46 trillion kilometers. Because the universe is so vast, kilometers would give unwieldy numbers, so astronomers use light-years. Note: a light-year measures distance, not time.
难度 专业 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
苏宜,《天文学新概论》第5版,科学出版社
Su Yi, Introduction to Astronomy, 5th ed., Science Press
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787030620477（豆瓣书目条目: 天文学新概论）
#光年 #距离单位 #天文尺度
什么是视差，天文学家怎么用它测距离？
What is parallax and how do astronomers use it to measure distance?
视差是从两个不同位置观察同一近处物体时，它在远处背景上相对移动的现象。天文学家在地球公转轨道两端（相隔约半年）拍摄邻近恒星，测其相对遥远背景的微小位移角（半年视差），再用三角法算出距离，1秒差距约3.26光年。视差是确定恒星距离最可靠的直接方法，盖亚卫星已测上亿颗恒星的视差。
Parallax is the apparent shift of a nearby object against a distant background when viewed from two different positions. Astronomers photograph nearby stars six months apart at opposite ends of Earth's orbit, measure the tiny shift angle (the annual parallax), and use trigonometry to find distance; one parsec is about 3.26 light-years. Parallax is the most reliable direct distance method, and Gaia has measured it for over a billion stars.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
苏宜,《天文学新概论》第5版,科学出版社
Su Yi, Introduction to Astronomy, 5th ed., Science Press
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787030620477（豆瓣书目条目: 天文学新概论）
#视差 #距离测量 #盖亚
为什么夜空是黑的而不是被无数星星照亮？
Why is the night sky dark instead of lit up by countless stars?
这被称为奥伯斯佯谬。一种解释是宇宙的年龄有限，远处星光还没来得及到达我们；同时宇宙在膨胀，遥远星光被红移削弱。再加上恒星数量虽多但并非无限，所以夜空总体是暗的。这一悖论引导人们认识到宇宙的有限年龄与膨胀。
This is Olbers' paradox. One resolution is that the universe is finitely old, so distant starlight has not yet arrived, and expansion redshifts and weakens far light. Also, while stars are many, they are not infinite in number, so the sky stays dark overall. The paradox helped reveal the universe's finite age and expansion.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
苏宜,《天文学新概论》第5版,科学出版社
Su Yi, Introduction to Astronomy, 5th ed., Science Press
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787030620477（豆瓣书目条目: 天文学新概论）
#奥伯斯佯谬 #夜空 #红移
我们肉眼在晴天晚上大约能看到多少颗星星？
How many stars can we see with the naked eye on a clear night?
在远离光污染的黑暗夜空，肉眼大约能看到3000到6000颗星星，具体取决于视力、视野和季节。因为地球挡住了一半天空，同一时刻通常只能看到其中约一半。城市里由于光污染，能看到的星往往只有几十颗。
Under a dark sky far from light pollution, the naked eye can see roughly 3,000 to 6,000 stars, depending on eyesight, view, and season. Since Earth blocks half the sky, you typically see only about half at any moment. In cities, light pollution reduces this to only a few dozen.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
苏宜,《天文学新概论》第5版,科学出版社
Su Yi, Introduction to Astronomy, 5th ed., Science Press
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787030620477（豆瓣书目条目: 天文学新概论）
#可见恒星 #肉眼 #光污染