What is the moon made of, and how did it form? Learn about the moon's violent origins, how its phases shaped the earliest calendars, and how humans first explored Earth's only natural satellite half a century ago.
The moon, Earth’s sole natural satellite, is our constant companion. It has circled our planet for billions of years, since before the first sparks of life flickered in the oceans—before Earth was even cool enough to have oceans.
But its seemingly tranquil position in modern night skies stems from a remarkably tumultuous past. It formed some 4.5 billion years ago, when the solar system was in its infancy and comets, meteors, and asteroids ricocheted throughout. One such collision, between Earth and a Mars-sized orb, likely flung molten rock out into space, some of which coalesced and cooled to form what we now know as the moon.
This early formation and close ties with young Earth makes the moon one of the most
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