Three centuries ago Isaac Newton and his contemporaries sought to understand the details of lunar motion in terms of Newton's theory of gravity. Today, our most precise confirmations of key aspects of Albert Einstein's relativistic theory of gravity are achieved by measuring features of the Moon's orbit to 1‐centimeter precision using a technique known as lunar laser ranging (LLR). These present‐day measurements address some of the same questions posed by Newton. Do Earth and the Moon (figure 1) fall toward the Sun at the same rate? What, in detail, produces the precession of the lunar orbit's major axis?

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