The Sahara’s climatic changes are because of Earth’s precession, a wobble on its axis that completes a cycle roughly every 26,000 years. Today the Sahara is angled away from the Sun by about 23.5°, and Earth makes its closest approach to the Sun (perihelion) during wintertime in the Northern Hemisphere. During African Humid Periods, in which the Sahara is covered with vegetation, perihelion and summertime in the Northern Hemisphere happen at the same time.
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