The rhythm of the phases of the moon has guided humanity for millennia; for instance, calendar months are roughly equal to the time it takes to go from one full moon to the next. But the moon's orbit and phases can seem mysterious. for example, the moon always shows us the same face, but it's always changing size as how much of it we see depends on the moon's position in relation to Earth and the sun.
The moon is a bit more than one-fourth (27%) the size of Earth, a much larger ratio (1:4) than any other moons to their planets. This means the moon has a great effect on our planet and may even be a major factor in making life on Earth possible.
There are various theories about how the moon was created, but recent evidence indicates it formed when a huge collision tore off a chunk of the primitive molten Earth, sending the raw ingredients for the moon into orbit.
Scientists have suggested the impacting object was likely about 10% the mass of Earth and about the size of Mars. Because Earth and the moon are so similar in composition, researchers have concluded that the impact must have occurred about 95 million years after the formation of the solar system, give or take 32 million years. (The solar system is roughly 4.6 billion years old.)
In 2015, new research gave further weight to this theory, using simulations of planetary orbits in the early solar system as well as newly uncovered differences in the abundance of the element tungsten-182 detected in the Earth and the moon.
While this theory, most commonly known as the large impact theory, is the dominant theory in the scientific community, there are several other ideas for the moon's formation. These include the concept that the Earth captured the moon, that the moon fissioned out of the Earth or even that Earth may even have stolen the moon from Venus.
The moon very likely has a very small core, just 1% to 2% of the moon's mass and roughly 420 miles (680 km) wide. It likely consists mostly of iron, but may also contain large amounts of sulfur and other elements.
The crust that includes the lunar surface averages some 42 miles (70 km) deep. The outermost part of the crust is broken and jumbled due to all the large impacts the moon has endured , with the shattered zone giving way to intact material below a depth of about 6 miles (9.6 km).
Like our solar system's four innermost planets, the moon is rocky. It's pockmarked with craters created by asteroid impacts millions of years ago and, because there is no weather, the craters have not eroded.
Orbiting spacecraft have found traces of water on the lunar surface that may have originated from deep underground. They have also located hundreds of pits that could one day house explorers living on the moon long-term.
Ongoing observations from the Lunar Reconnaissance Orbiter (LRO) have shown that water is more abundant on slopes facing the lunar south pole, although scientists do caution that the water quantity is comparable to an extremely dry desert. Meanwhile, a 2017 study suggested the moon's interior could be abundant in water too.
High tides refer to water bulging up from Earth's surface, and low tides when water levels drop. High tide occurs on the side of the Earth nearest the moon due to gravity, and on the side farthest from the moon due to the inertia of water. Low tides occur between these two humps.
The pull of the moon is also slowing the Earth's rotation, an effect known as tidal braking, which increases the length of our day by 2.3 milliseconds per century. The energy that Earth loses is picked up by the moon, increasing its distance from the Earth, which means the moon gets farther away by 1.5 inches (3.8 centimeters) annually.
The moon's gravitational pull may have been key to making Earth a livable planet by moderating the degree of wobble in Earth's axial tilt, which led to a relatively stable climate over billions of years in which life could flourish.
During eclipses, the moon, Earth and sun are in a straight line, or nearly so. A lunar eclipse takes place when Earth is directly between the sun and the moon, casting Earth's shadow onto the moon's face. A lunar eclipse can occur only during a full moon.
Depending on the degree to which the moon blocks the sun as seen from a particular location on Earth, a solar eclipse can be total, annular or partial. Total solar eclipses are rare in a given location because the shadow of the moon is so small on the Earth's surface.
But the moon's axis is tilted by only about 1.5 degrees, so the moon doesn't experience noticeable seasons. This means that some areas are always lit by sunlight, and other places are perpetually draped in shadow.
Some ancient communities believed the moon was a bowl of fire, while others thought it was a mirror that reflected Earth's lands and seas, but ancient Greek philosophers knew the moon was a sphere orbiting the Earth whose moonlight reflected sunlight.
The Renaissance astronomer Galileo Galilei was the first to use a telescope to make scientific observations of the moon, describing in 1609 a rough, mountainous surface that was quite different from the popular beliefs of his day that the moon was smooth.
In 1959, the Soviet Union sent the first spacecraft to impact the moon's surface and returned the first photographs of its far side. This spurred a series of Cold War-era uncrewed missions launched by both the Soviet Union and the United States to observe the moon's surface.
Many of these early moon probes were failures or only partially successful. However, over time, these missions began to return information about the moon's surface and geological history. The United States launched a series of missions dubbed Pioneer, Ranger and Surveyor, while the Soviet Union sent probes under the names Luna and Zond.
In 1969, Apollo 11 landed the first astronauts on the moon, followed by five more successful surface missions (and one, Apollo 13, that didn't make to the moon but returned home safely). The moon remains the only extraterrestrial body that humans have ever visited.
Since then, a host of other government space agencies have also joined the moon rush, including Japan, the European Space Agency, China, India and Israel. China is the only one of those countries to successfully operate on the surface of the moon; landers sent by the latter two nations crash-landed.
Meanwhile, in 2019, the administration led by President Donald Trump announced that it was directing NASA to work on returning humans to the moon by 2024. The initiative, dubbed the Artemis program, would rely on commercial and international partners to support a sustainable crewed exploration program powered by NASA's heavy-lift rocket, the Space Launch System.
The term "blue Moon" has not always been used this way, however. While the exact origin of the phrase remains unclear, it does in fact refer to a rare blue coloring of the Moon caused by high-altitude dust particles. Most sources credit this unusual event, occurring only "once in a blue moon," as the true progenitor of the colorful phrase.
Use nearby objects to remember how far 23 feet 9 inches is from the basketball. Ask others to place the tennis ball where they think the moon is.They will be very surprised when you show them how far away it needs to be!
David Brinkley: And now, the Russians are talking about shooting up something that will hit the moon, and possibly, even make some kind of mark on it, visible from the earth, the kind thing that a month ago would have sounded like a joke, but in Washington now anyone who cares to laugh at this does so at his own risk.
President Kennedy: I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to the earth. No single space project in this period will be more impressive to mankind or more important for the long-range exploration of space and none will be so difficult or expensive to accomplish. I believe we should go to the moon, but I think every citizen of this country as well as the members of the Congress should consider the matter carefully in making their judgement to which we have given attention over many weeks and months. Because it is a heavy burden, and there is no sense in agreeing or desiring that the United States take an affirmative position in outer space unless we are prepared to do the work and bear the burdens to make it successful.
David Brinkley: If we decide to go ahead with the exploration of space including putting a man on the moon within the next ten years, we must be prepared to spend the money and do the work. And as he described the work and described the money, they both are considerable.
John Logsdon: In 1963, severe criticism of Apollo began to emerge from a variety of quarters. So Kennedy was concerned about this growing criticism and about his re-election prospects. And in that context, Kennedy returned to the idea of cooperating with the Soviet Union. Why not do it together? Including joint missions to the moon.
Surely we should explore whether the scientists and astronauts of our two countries indeed, of all the world, cannot work together in the conquest of space. I include among these possibilities a joint expedition to the Moon. Sending someday in this decade to the moon, not the representatives of a single nation, but the representatives of all of our countries.
Bill Anders: We had been told, that the Soviets were going to try to launch the first manned-flight up and around the Moon. It was proven that they, indeed, tried it unmanned, they had selected crew to fly a manned flight. Many of the earlier flights were unsuccessful for various reasons. So, unbeknownst to us, the Russians got cold feet. But NASA under the threat of having the Soviets scoop them yet again, decided to shuffle the Apollo flights, take Apollo 8 whose lunar module was behind schedule anyway, give us the first Saturn 5, and on that we would just go around the moon without a Lunar Module. 781b155fdc