On July 20, 1969, the world sat in anticipation around radios and TV screens as Apollo 11 astronaut Neil Armstrong became the first human to set foot on the moon and continued to fuel our fascination with the moon.
The U.S. proceeded to land humans on the moon six additional times — 12 astronauts in total — with a final lunar touchdown in 1972. While the U.S. ceased sending astronauts to the moon after that, scientists have continued to explore the moon with the help of lunar landers, rovers, and orbiters.
Other countries have also launched successful lunar research programs. In 2007, the China National Space Administration (CNSA) embarked on its Chinese Lunar Exploration Program, which launched the robotic Chang'e missions to explore the moon. The missions have successfully sourced lunar soil, provided high-resolution images of the lunar surface, and explored parts of the moon that have never been surveyed before.
As scientists around the world have been studying the moon for more than 50 years, we've learned a lot since that first lunar landing — and we're still learning today. Here are some interesting facts that have been uncovered about Earth’s natural satellite.
The Moon and Earth Are the Same Age
Measures of lunar rocks show that the moon is roughly the same age as Earth. The moon was formed 4.5 billion years ago in the wake of a collision between Earth and a large foreign body, which caused debris from the impact to float into space. The moon is now roughly 238,855 miles from Earth, and its radius is about 1,080 miles, which is one-third the size of our planet.
Marias and Highlands Comprise the Moon’s Surface
The moon has a thin atmosphere incapable of shielding itself from cosmic rays and colliding objects. Because of this, the moon is regularly bombarded with asteroids and comets that have led to the many craters on its surface and also a thin layer of space dust that coats the entire surface of the moon.
The dark areas of the surface are impact sites known as “marias,” derived from the Latin word mare, which means “sea.” Marias are very flat and cover 17% of the moon’s surface. On the opposite end of the spectrum are highlands, which are light in color and mountainous. Highlands make up 83% of the moon’s surface.
The Moon Is Constantly Moving Away From Earth
Earth’s gravitational field is responsible for the moon’s stable orbit around the planet. However, Earth is not a perfect sphere and exerts a non-uniform gravitational pull on the moon. This phenomenon is responsible for the shift in tides as a result of lunar cycles, and it’s also causing the moon to expand its orbit ever so slightly. Each year, the moon drifts roughly 1 inch away from Earth. After 500 million years, this slight drift will place the moon roughly an additional 8,000 miles away from Earth.
The Moon Inspired the Word “Lunatic”
Humans have long been fascinated with the moon’s ability to influence the tides and climate. These curiosities have been embodied in everything from early astronomy to modern agriculture. Medieval societies believed that lunar cycles influenced behaviors to the point of inducing madness in some individuals. This is why the prefix “luna” in “lunatic” is the Latin word for “moon.” While there is no longer evidence that the moon’s cycles can make people go mad, modern studies do show that lunar cycles can influence human sleep patterns.
There Is No “Dark Side of the Moon”
It takes the moon 27.3 days to complete one full rotation around its own axis, which is roughly the same period of time it takes to orbit the Earth once — 29.5 days. Because of this, the moon always shows the same side to Earth. The “hidden” side is often referred to as the “dark side of the moon,” but in actuality, one side isn’t darker than the other. Both sides of the moon experience two weeks of sunlight and two weeks of darkness, which cause what we refer to as the phases of the moon.
The “dark side” is often called the “far side” since it’s not permanently dark.