What's Up - July 2019

What's Up for July? NASA is celebrating the 50th anniversary of the Apollo 11 mission making the first human landing on the Moon, while looking forward to the future of lunar exploration. So this month, a special edition of What's Up: Here are five things about the Moon that you can share with others when you're gazing up at our natural satellite.

How far away is the Moon?

The Moon is farther away from Earth than people often think. A good ballpark number to remember is that the Moon is about a quarter of a million miles away, or about 400 thousand kilometers. It's such a big gap that you could just about fit the other seven major planets into the space between the two worlds.

Astronauts from three of the Apollo missions, including Apollo 11, placed special reflectors on the lunar surface that are still used to determine the Moon's distance with extreme precision. In fact, they've revealed that the Moon is moving away from Earth by about an inch and a half per year.

How big is the Moon?

This one's another easy approximation to remember: The Moon is about one-fourth the size of Earth in diameter. It's just about as wide as the United States.

What color is the Moon?

The Moon doesn't emit its own light - it reflects light from the Sun. And up close, the Moon's surface is mostly gray, like old, well-worn asphalt.

Why do we always see the same side of the Moon?

Now it may not look like it, but the Moon really does rotate on its axis, much like Earth. We always see essentially the same face of the Moon because it orbits around Earth in the same amount of time it takes to rotate. The reason is related to gravity and the same forces that cause daily ocean tides.

A side note is that, since it's rotating, there really is no permanent dark side of the Moon. The changing phases of the Moon demonstrate how the portion of its surface that's lit by the Sun revolves around the Moon every month, over the course of the lunar day.

What are the dark areas on the Moon?

One of the main things you notice when observing the Moon is that it has these bright and dark areas across its surface. (Everybody's familiar with the "Man in the Moon," right?)

The dark areas are known as "mare," the Latin word for seas. The lunar mare are volcanic basins created in the aftermath of ancient impacts billions of years ago. After the impacts, the craters filled with lava, which eventually cooled to form smooth, dark plains.

One of the most famous mare is the Sea of Tranquility. This was the landing site chosen for Apollo 11, in part because it was fairly smooth and level.

To locate the Sea of Tranquility, look for these two large, dark markings that overlap. If you're facing south, they'll be on the Moon's right side. Tranquility is the lower of the two, and the Apollo 11 landing site is right here.

50 years on, NASA continues to reveal the Moon's secrets, with an eye toward sending the next human astronauts there in the near future.

Here are the phases of the Moon for July.

You can learn more about Apollo and NASA's future plans for the Moon at nasa.gov.

I'm Preston Dyches from NASA's Jet Propulsion Laboratory, and that's What's Up for this month.