The sun and the moon are constants in our lives. Not even a cloudy day or night can convince us that they aren't right there where they always are, hovering above us like a watchful eye.

The moon has always been more mysterious to us than the sun, however. It comes out at night, providing just a glimmer of light in an otherwise dark night. And it looks different in the sky from night to night, sometimes just a sliver of itself. This changing appearance is because of the lunar cycle.

Every 29.5 days, the moon completes this cycle, going from new moon to waxing crescent to first quarter to waxing gibbous to full moon to waning gibbous to third quarter to waning crescent and starting all over again, according to the National Aeronautics and Space Administration. This lunar cycle is why we experience a full moon just about once a month — except for once in a blue moon when the cycle allows for there to be two full moons in a month, the second of which is, of course, called a blue moon.

The moon has long been a source of great curiosity to us Earth dwellers and 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 for us. 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. One of the goals of NASA's Apollo program, which included 11 missions to space and six landings on the moon between 1962 and 1972, was to explore the moon in part to determine its origin, according to the Natural History Museum.

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 museum reports. 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 during Apollo missions to the moon show similarities in Earth's and the moon's chemical makeup as well as their isotopes. 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. There are some pretty extreme temperature swings on the moon, however. In the daylight, temperatures at the moon's Equator can reach as high as 250 degrees Fahrenheit, and at night the temperatures can drop as low as 208 degrees below zero Fahrenheit, according to NASA. That's a swing of more than 450 degrees! 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, NASA reports. 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 frigid 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. If you've ever lived near the ocean or been on a beach vacation to the ocean, you probably know the oceans' have high tides and low tides. These 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, according to the National Oceanic and Atmospheric Administration. 

We experience high tides because of the moon's gravitational force on Earth. The gravitational forces of the sun play a role too, but to much less of an extent than the moon. 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, NOAA reports. 

The moon's gravity creates what is called a tidal force, and that force causes water to bulge out from Earth's surface at the points both closest and farthest from the moon, according to the NOAA. 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

The phrase "the dark side of the moon" most famously refers to a Pink Floyd album of the same name, but it might be surprising to learn it isn't really dark on the dark side of the moon. Or at least it isn't 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, PBS reports. 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 those of us here 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, so that means we are always facing the same side of the moon, according to PBS. We always see the same 60% of the moon, and the other 40% is never visible to those of us who are Earth bound. 

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 us on Earth, but it's slowly slipping farther and farther away. The movement is very gradual — it only gets about 1 inch farther away every year, NASA reports.

The reason it is moving farther away is because of the effects of the moon's gravity on Earth, the BBC reports. 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, Space.com reports.