In 1776, the moon was a clock, a calendar and a streetlight — and it was 31 feet closer to Earth

After Americans declared independence on July 4, 1776, a waning gibbous moon rose in the night sky. To the people celebrating the birth of a new nation, it would have looked much the same as the moon we see today. But there was one subtle difference: 250 years ago, the moon was about 31 feet (9.4 meters) closer to Earth than it is now.

"The moon is currently drifting away from Earth at a rate of about 3.8 centimeters [1.5 inches] per year, which is coincidentally roughly the same speed at which human fingernails grow," says Seth McGowan, president of the Adirondack Sky Center & Observatory in Tupper Lake, New York.

That 31 feet may sound significant, but against the moon's average distance from Earth of 238,855 miles (384,400 km), it's effectively nothing. In fact, the moon's elliptical orbit causes its distance from Earth to vary by about 26,000 miles (43,000 km) every month as it moves between perigee, its closest point to Earth, and apogee, its farthest. "The tiny 31-foot shift over 250 years is entirely swallowed up by that m...