The sun and the moon are constants in our lives. Even on a cloudy day or night we know they are right where they always are and will be visible again once the clouds clear.
The moon has always been more mysterious to us than the sun. It comes out at night, providing just a glimmer of light in an otherwise dark sky. And it looks different from night to night. Sometimes it is just a sliver of itself. This changing appearance is because of the lunar cycle.
Every 29.5 days, the moon completes the lunar cycle. You might have learned about the stages of the lunar cycle in school. It starts with a new moon then goes to waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third quarter and then waning crescent. Then it starts all over again.
This lunar cycle is why we experience a full moon just about once a month. Because of the lunar cycle, there is a full moon every 29.5 days.
The moon has long been a source of great curiosity to us. It was the focus of the Space Race in the mid-20th century. We set out to send man to the moon, which the U.S. successfully accomplished on July 21, 1969, when Neil Armstrong became the first person to set foot on the moon.
Even though we've conquered the moon, it continues to be a source of curiosity and inspiration. Here is your chance to learn more about it.
Its origin isn't entirely known
We know a lot about space, but one thing scientists can't be entirely certain about is how the moon formed. From 1962 to 1972, NASA ran its Apollo program. One of the goals of the program was to explore the moon in part to learn its origin. In the 10 years of the Apollo program, NASA launched 11 missions to space, including six moon landings.
Evidence from the Apollo program led to one widely accepted theory about the origin of the moon called the giant impact theory. It is believed that the moon formed billions of years ago when Earth collided with a planet similar in size to Mars. The collision created a lot of debris, and that debris collected into an object that began to orbit Earth. That object is the moon.
Scientists theorize that the moon formed as a result of a collision between Earth and another planet because rock samples collected from the moon show similarities in Earth's and the moon's chemical makeup. Meteorites from the moon have also helped scientists better understand the composition of the moon.
The temperature swings are extreme
The moon does not have atmosphere like Earth does, so it does not experience weather conditions like rain, snow and wind. However, there are some pretty extreme temperature swings on the moon. In the daylight, temperatures at the moon's Equator can reach as high as 250 degrees Fahrenheit. At night the temperatures can drop as low as 208 degrees below zero Fahrenheit. That's a swing of more than 450 degrees!
Words to know
Atmosphere: The mixture of gases around Earth.
Bulge: To swell or curve outward.
Gibbous: The stage of the moon when it is more than half but not completely full.
Miniscule: Extremely small.
Here on Earth, the greatest recorded swing in temperature in a 24-hour period occurred in January 1972 in Loma, Montana. On Jan. 14, the town of Loma recorded a temperature of 54 degrees below zero Fahrenheit at 9 a.m. Jan. 14. At 8 a.m. Jan. 15, the recorded temperature was 49 degrees Fahrenheit, an increase of 103 degrees, according to Guinness World Records.
The reason for such extreme temperature swings on the moon is its lack of atmosphere. Without atmosphere, heat from sunlight cannot be either trapped or spread. And as cold as it can get on the moon's surface, its craters can be even colder, particularly at the poles because sunlight doesn't reach these spots. NASA's Lunar Reconnaissance Orbiter has recorded temperatures as low as 410 degrees below zero Fahrenheit in these icy craters.
It controls the oceans' tides
The moon may be hundreds of thousands of miles away from Earth, but it has a significant impact on our oceans. Have you ever been on a beach vacation to the ocean? Did you experience the high tide and low tide?
Our coastal areas experience two high tides and two low tides every 24 hours and 50 minutes. Why 24 hours and 50 minutes? Because that is the length of a lunar day, or how long it takes for a point on Earth to make a full rotation and return to the same point in relation to the moon.
We experience high tides because of the moon's gravitational force on Earth. The moon has gravity, but it is only about one-sixth as strong as Earth’s gravity. Tides are essentially long waves. When the crest, or high point, of the wave reaches the coast, it's the high tide. When the trough, or low point, of the wave reaches the coast, it's the low tide.
The moon's gravity creates what is called a tidal force. That force causes water to bulge out from Earth's surface at the points both closest and farthest from the moon. The bulges are the high tides, and the points between the farthest and closest points to the moon experience low tides. As Earth rotates, the tides shift too.
The dark side isn't really dark
Have you heard the phrase "the dark side of the moon?" If so, it might be surprising to learn it isn't really dark on the dark side of the moon. Or at least it is not any darker than anywhere else on the moon.
It's just as dark on what we call the dark side of the moon as it is everywhere else on the moon. The dark side of the moon would more appropriately be called the far side of the moon.
The dark side — or far side — of the moon is never visible to us on Earth because of how the moon rotates. The moon makes a complete rotation on its axis in the exact same amount of time as it takes for it to orbit Earth. That means we are always facing the same side of the moon. We always see the same 60% of the moon, and the other 40% is never visible to those of us who are Earth bound. That is the part we call the dark side of the moon.
It's getting farther and farther away
The moon's distance from Earth is not always the same because its orbit around Earth is not a perfect circle. On average, the moon is 238,855 miles away from Earth, but it's slowly slipping farther and farther away. The movement is very gradual, though. It only gets about 1 inch farther away every year.
The reason it is moving farther away is because of the effects of the moon's gravity on Earth. Just an inch a year is a minuscule distance when you consider that the moon is more than 200,000 miles away. It will take millions of years before the moon becomes noticeably farther away from Earth.
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