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Curious Kids<\/a> is a series for children of all ages. If you have a question you\u2019d like an expert to answer, send it to CuriousKidsUS@theconversation.com<\/a>.<\/p>\n \u201cIs the Moon getting farther away from Earth?\u201d \u2013 Judah, 9, Broken Arrow, Oklahoma<\/strong><\/p>\n<\/blockquote>\n The Moon is getting 1\u00bd inches (3.8 centimeters) farther away<\/a> from the Earth every year. <\/p>\n Scientists measure the distance to the Moon by bouncing lasers off mirrors<\/a> placed there by space probes and astronauts. <\/p>\n By measuring the amount of time it takes light to travel to the Moon and back, scientists can very precisely measure the distance to the Moon and how the distance changes.<\/p>\n The distance to the Moon actually changes over a single month as it goes around the Earth. The Moon is typically 239,000 miles (385,000 km) away from the Earth<\/a>, but its orbit is not a perfect circle<\/a> and changes by about 12,400 miles (20,000 km) as it orbits the Earth. This change is why some full moons are a bit bigger than others; these are called supermoons<\/a>.<\/p>\n As an astrophysics researcher<\/a>, I\u2019m interested in the motion and interaction of objects such as planets, stars and galaxies. The motions of the Earth and Moon have many interesting consequences, and studying how they move over time can help researchers better understand how each has changed over the 4\u00bd billion years since the Earth and Moon formed.<\/p>\n Tidal forces<\/p>\n So, why is the Moon getting farther away? It\u2019s all because of tides.<\/p>\n Tides come from a difference in gravity<\/a> across an object. The force of gravity exerted by the Moon is about 4% stronger on the side of Earth that faces toward the Moon, compared to the opposite side of the Earth facing away, because gravity gets weaker with distance. <\/p>\n This tidal force causes the oceans to slosh around in two bulges that point toward and away from the Moon. They do this because the gravitational force pulling on Earth by the Moon isn\u2019t just an average force that\u2019s the same strength everywhere. The Moon\u2019s gravity is strongest on the closer side of the Earth, creating a bulge of water pointing toward the Moon. It\u2019s weaker on the opposite side of the Earth, which leaves another bulge of water that lags behind the rest of the Earth. <\/p>\n A NASA animation, not to scale, shows how the Moon creates tides on the Earth. The water in the oceans sloshes toward and away from the Moon. As the Earth rotates, these bulges move around and keep pointing at the Moon because of its gravitational pull. In New York City or Los Angeles, the water level can change by about 5 feet<\/a> due to these tidal bulges.<\/p>\n These liquid bulges do not quite line up with the Moon \u2013 they \u201clead\u201d it a little bit because the Earth is rotating and dragging them forward. These bulges also exert a gravitational pull back on the Moon. The bulge closer to the Moon isn\u2019t just pulling the Moon toward the center of the Earth, but also a little bit ahead in its orbit \u2013 like the boost a sports car gets as it goes around a curve. <\/p>\n As the Moon orbits the Earth, the tidal bulges do not exactly point toward the Moon, but instead a little bit ahead of it because of friction between the bulges and the rotating Earth. This forward pull from the closer tidal bulge causes the Moon to speed up, which causes the size of its orbit<\/a> to increase. Think of a baseball player hitting a home run. If the player hits the ball faster at home plate, it\u2019ll zoom higher up into the sky.<\/p>\n So the bottom line is that the gravity of the closer tidal bulge on the Earth is pulling the Moon forward, which increases the size of the Moon\u2019s orbit. This means that the Moon gets slightly farther away from the Earth. This effect is very gradual and only detectable on average over years.<\/p>\n Does the Moon\u2019s increasing distance affect Earth?<\/p>\n The Moon gains momentum<\/a> as its orbit gets bigger. Think about spinning a weight attached to a string. The longer the string, the more momentum the weight has, and the harder it is to stop.<\/p>\n Because the Earth is doing the work of increasing the Moon\u2019s momentum, the Earth\u2019s rotation slows down<\/a> in turn, as its momentum goes to the Moon. To put it another way, as the Moon\u2019s orbital momentum increases, the Earth\u2019s rotational momentum decreases in exchange. This exchange makes a day get very slightly longer. <\/p>\n But don\u2019t worry, these effects are so small: 1.5 inches per year compared to a distance of 239,000 miles (384,000 km) is just 0.00000001% per year. We\u2019ll keep having eclipses<\/a>, tides and days that last 24 hours for millions of years.<\/p>\n Was the Moon closer to us in the past?<\/p>\n The Earth\u2019s days were shorter in the past.<\/p>\n The Moon probably formed<\/a> around 4.5 billion years ago, when a young Earth was hit by a Mars-size protoplanet<\/a>, causing a lot of material to get knocked off into space. <\/p>\n Eventually, that material formed the Moon, and it was initially much closer to the Earth. Back then, you\u2019d see the Moon much bigger in the sky. <\/p>\n<\/p>\n A NASA simulation of the collision between early Earth and a now-destroyed protoplanet that likely created the Moon.<\/p>\n By examining fossilized clam shells for material showing their daily growth patterns, paleontologists found evidence that 70 million years ago<\/a> \u2013 near the end of the time of dinosaurs \u2013 the day was only 23.5 hours long, just as predicted by astronomical data.<\/p>\n What will happen in the future?<\/p>\n So, will the Moon eventually escape from the Earth\u2019s gravitational pull as it moves away?<\/p>\n If we fast-forward tens of billions of years into the future, eventually the Earth\u2019s rotation could slow down until it is tidally locked<\/a> with the Moon. That means that it would take just as long for the Earth to rotate as the Moon does to orbit. At this point, the Moon would stop getting more distant, and you would see the Moon only from one side of the Earth.<\/p>\n<\/p>\n A NASA video shows how the Sun might appear as a red giant billions of years in the future.<\/p>\n But two things will stop that from happening. First, in a billion years or so, the Sun will get brighter<\/a> and boil away the oceans. Then, there won\u2019t be large tidal bulges of water to cause the Moon to get more distant. A few billion years later, the Sun will expand into a red giant<\/a>, probably destroying the Earth and the Moon. <\/p>\n But these events are so far in the future that you don\u2019t need to worry about them. You just get to enjoy tides on the beach, solar eclipses and our beautiful Moon.<\/p>\n\n
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\n NASA\/Vi Nguyen<\/a><\/p>\n![\"An](\"https:\/\/www.europesays.com\/us\/wp-content\/uploads\/2025\/09\/file-20250729-56-czakqe.gif\")
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\n NASA\/Vi Nguyen<\/a><\/p>\n