![]() ![]() “Over time, the moon stole the rotational energy of the Earth to bring it into an orbit higher and farther from the Earth”said Ross Mitchell, a geophysicist at the Institute of Geology and Geophysics of the Chinese Academy of Sciences and lead author of a new study published in Natural Geosciences. Day length was shorter because the moon was closer. The contraction causes the Moon’s crust to buckle, pushed together and upwards to form the cliffs, but scientists examining these cracks have observed that their positions are related to the pull of Earth’s gravity.Surprisingly, the length of the day may have been determined by the amount of oxygen in the Earth’s atmosphere, which in turn was determined by the abundance of photosynthesizing organisms.Īlthough we assume that our days last 24 hours, early in the history of life on our planet, days were even shorter. Young cliffs on the Moon, called lobate scarps, form due to the combined forces of the Moon contracting as its hot interior cools and Earth’s gravity pulling on the surface. It’s not as dramatic as the ocean tides ― think of it as the difference between trying to squish a balloon filled with water and a balloon filled with sand ― but these tides on the Moon are measurable using lasers, and in some cases their effects are visible. Well, just as the Moon’s pull slightly distorts Earth’s sphere, Earth’s gravity slightly deforms the Moon. ![]() But what about Earth’s much bigger gravitational influence on the Moon? After all, Earth has 80 times the Moon’s mass. We’ve talked a lot about the effect of the Moon’s gravitational pull on Earth. Credits: NASA/LRO/Arizona State University/Smithsonian Institution Cooling of the still-hot lunar interior is causing the Moon to shrink, but the pattern of orientations of the scarps indicate that Earth’s gravitational pull contributes to the formation of these cracks. Lobate scarps like the one shown here are like stair-steps in the landscape formed when the Moon’s crust is squeezed together, breaks, and is pushed upward to create a cliff. Thousands of young, lobate scarps have been revealed in Reconnaissance Orbiter Camera images. Neap tides occur around the first and last quarter phase of the Moon, when the Moon’s orbit around Earth brings it perpendicular to the Sun. Spring tides always happen when the Moon is at the full or new phase, which is when the Sun, Moon and Earth are in alignment. You can tell when a spring tide or neap tide is happening without being anywhere near the water. About a week later, when the Sun and Moon are at right angles to each other, the Sun’s gravitational pull works against the Moon’s gravitational tug and partially cancels it out, creating the moderate tides called neap tides. Twice a month, when the Earth, Sun, and Moon line up, their gravitational power combines to make exceptionally high tides where the bulges occur, called spring tides, as well as very low tides where the water has been displaced. But it’s a distant gorilla, about 390 times farther away than the Moon, which gives it a little less than half of the Moon’s tide-generating force. ![]() The Sun ― with about 27 million times the mass of the Moon ― is always the gorilla in the room when it comes to solar system equations. Now, the Moon is the biggest influence on Earth’s tides because of its proximity ― but it isn’t the only influence. To get a true estimate of the tides near you, you’ll have to check the local tides forecast. The tides we actually see at our shores are affected by everything from the shape of Earth’s continents to wind and storms. In addition, Earth isn’t a perfect, smooth sphere. This means that the high tide bulges are never directly lined up with the Moon, but a little ahead of it. When the Moon’s gravity pulls at Earth, the water doesn’t float outward, it just gets pushed and squeezed around on the globe, directed by both gravitational pull and other forces, until it ultimately ends up bulging out on the side closest to the Moon and the side farthest away.Ĭan you easily predict the tides by following the path of the Moon? Not really! First of all, because the Moon is orbiting in the same direction as the Earth rotates, it takes extra time for any point on our planet to rotate and end up exactly below the Moon. It’s easier to slide the water around on the table rather than lift it directly upwards. Now think about pouring a bucket of water out on a table. The strongest pull occurs on the points closest to the Moon, and the weakest on the points farthest away, but every bit of water is affected. This happens because the Moon’s gravity affects the entire Earth, pulling at every point on our planet. It might seem strange that the ocean would bulge on the side farthest from the Moon as well as the side closest to it. The low points are where low tides occur. In this simplified animation, Earth’s oceans bulge out on both the side closest to the Moon and the side farthest from the Moon. ![]()
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