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Dashboard Learning Paths Arab & Islamic Astronomy Modern Astronomy Tonight's Sky

Switches lessons to a dyslexia-friendly font with wider letter, word, and line spacing. In Arabic, only the spacing changes. Simulator

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Dashboard
Learning Paths
Arab & Islamic Astronomy
Modern Astronomy
Tonight's Sky
Core Concepts
Guided Tour

Our solar system

Overview
The Sun
The Planets
Earth
Mars

The wider universe

Stars
Constellations
Galaxies
Black Holes

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Space Missions
Timeline
Simulations
Glossary

Al-Biruni and the Mountain

How al-Biruni measured the Earth's radius from a single mountain, without ever crossing a plain.

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