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History of Astronomy
From Ptolemy's geocentric cosmos to Copernicus, Galileo, Kepler, Herschel, and Hubble — the instruments, catalogs, and observers who slowly turned the night sky into a mapped, measured, physical universe.
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Ptolemy to Copernicus: Moving the Center of the Universe
For 1,400 years the Earth sat at the center of the cosmos. It took a Polish canon in 1543 to move it — and even he did it with reservations.
Dmitry Shteynbuk · November 10, 2025 · 3 min read
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3 publishedHistory of Astronomy·
Hubble, Leavitt, and the Night the Universe Got Bigger
In 1912 Henrietta Leavitt found a rule that let astronomers measure vast cosmic distances. A dozen years later, Edwin Hubble used it to prove other galaxies existed.
Dmitry Shteynbuk · 3 min read
/articles/hubble-and-leavittHistory of Astronomy·
Galileo's Telescope: Four Moons That Changed Everything
In one winter of 1609–1610, a Paduan mathematician turned a toy Dutch spyglass on the sky and discovered enough to break the Aristotelian universe.
Dmitry Shteynbuk · 3 min read
/articles/galileos-telescopeTerms to know
Full glossary →- Ecliptic
- The apparent yearly path of the Sun through the sky.
- Parallax
- The apparent shift of a nearby star against the background as Earth orbits the Sun.
- Cepheid variable
- A pulsating giant star whose period reveals its true luminosity.
- Redshift
- The stretching of light to longer wavelengths as an object moves away.
- Constellation
- One of 88 regions the sky is divided into by the IAU.
- HR diagram
- The Hertzsprung–Russell diagram: luminosity plotted against temperature.