Reflectors placed on the moon during manned moon missions have let earthly astronomers accurately measure the moon’s distance. That’s how we know that – today – the moon’s distance from Earth is increasing at a rate of about 1.6 inches (4 cm) per year. What we haven’t known with any accuracy is how fast the moon was retreating long ago. Now researchers have announced results of new dynamic model – a computer simulation over time – based on the current size of the moon’s equatorial bulge. The model sets parameters on how fast or slowly the moon was receding from Earth, billions of years ago. It has implications for what the Earth, moon and other solar system bodies were like early in the history of our solar system.

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