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天文与航天科普，每篇讲清楚一个现象、一次任务或一段历史。
The First Time Humans Heard Two Black Holes Collide
September 14, 2015. 09:50:45 UTC.
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Mercury: A Day Longer Than Its Year, Ice at the Poles
On March 29, 1974, Mariner 10 passed 703 km above Mercury — the first close look at the planet closest to the Sun. Fifty-two years and two spacecraft later, its magnetic field is still unexplained.
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The 0.01% Wink That Found 6,000 Worlds
A planet is a barely noticeable flicker. When an Earth-sized world passes in front of its star, the star dims by about 0.01% — the equivalent of watching a 100-watt bulb lose 0.01 watts from across…
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Neptune: The Planet Found With Pen and Paper
In 1846 Johann Galle found Neptune in under an hour, less than 1 degree from where Le Verrier's math pointed. Newton's gravity triumphed. The later Planet X was a mistake.
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Atmospheric Reentry: Why Capsules Don't Burn Up
At nearly 8 km/s, a capsule is heated less by friction than by air it compresses to over 10,000 K. A blunt shape, an ablative heat shield and a narrow corridor bring it home.
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SN 1054: The Guest Star in the Song Dynasty Records
In 1054, Song dynasty astronomers logged a guest star seen in daylight for 23 days. Nearly 900 years later, it was confirmed as the supernova that created the Crab Nebula.
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The Roche Limit: Why Saturn's Rings Stay Rings
Within about 2.2 Saturn radii, tides tear an icy moon apart and stop fragments from regrouping. Saturn's main rings end right at this line, the Roche limit.
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Interstellar Visitors: Three Fleeting Messengers
Since 2017 we have confirmed three objects from other star systems: ʻOumuamua, Borisov and 3I/ATLAS. Each passed through once, too fast for the Sun to hold.
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The Hubble Deep Field: Ten Days Staring at "Empty" Sky
In December 1995, Hubble spent ten days on a seemingly blank patch of Ursa Major, taking 342 exposures. The image held about 3,000 galaxies and changed how we see galaxy evolution.
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The Webb Telescope: Why Observe in Infrared from L2
Cosmic expansion stretches the light of the earliest galaxies into the infrared. To see it, Webb carried a 6.5 m gold-coated mirror and a five-layer sunshield to Sun–Earth L2.
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The Deep Space Network: Hearing Voyager's Whisper
Voyager 1 transmits on about 22 watts, and its signal reaches Earth at around 10⁻¹⁸ W. Three complexes 120° apart, 70 m dishes and antenna arraying are why we can still hear it.
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Phobos: The Moon Falling Toward Mars
Phobos orbits just 6,000 km above Mars and is slowly falling toward it. Japan's MMX spacecraft launched on October 20, 2026, to bring a sample of it back in 2031.
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Europa: An Ocean Under the Ice With Twice Earth's Water
Europa's surface sits near -160°C, yet under its ice there is very likely an ocean holding about twice the water of Earth's oceans. Europa Clipper reaches Jupiter in 2030.
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