Why is it possible to see the same spot on the moon every night?

Answer 1

Because of the proximity of the moon to the earth and the effect of the earth's gravitation on the moon, the moon has experienced tidal locking and is now in what is called synchronous orbit about the earth. We always see the same side of the moon because it makes one rotation about its axis for every orbit it makes about the earth. Exactly. The curious person would follow the related links below to get more of the particulars.

Answer 2

Because it is "tidally-locked" to the Earth. The Earth's gravity slows down the moon's rotation, so that it rotates at the same speed as it revolves around the Earth. Imagine a person who walks around a center pole, but shifts their body so they are always facing it as they walk.

Just as the Moon's gravity exerts a force on the oceans of the Earth, the Earth's gravity exerts a force on the Moon. For the Earth's oceans, the tides make the water shift around, rising and falling.

The Moon is solid, without any liquid that could flex and deform under the gravity of the Earth. So for the Moon, the effect was to slow down its rotation, and eventually made it equal to the orbital period. The same effect, at a much smaller scale, is affecting the Earth, and the Earth's rotation is slowing down. In a few million years, the day will be 25 hours long.

Short :

(1) initially, when the earth-moon system was young, the force of gravity from the earth produced bulges on the moon (the gravity force in this case is called a "tidal force") that MOVED across the moon's surface like a wave (in a VERY exaggerated view, the moon looked like a football with one end pointing to the earth and the other end pointing exactly opposite--in actuality, the tidal bulges are not large and not as pointy as on a football)

(2) the bulge-wave though didn't move at the same rate as the line connecting the earth and the moon moved on the moon's surface (in other words, the football can't initially always have one of its two pointy ends pointed at the earth)

(3) over TIME, though, the bulge-wave slows down its progress across the moon's surface as the moon's football shape "learns" to lock itself into step with the earth so the football's end (one of the two ends that is--doesn't matter which) EVENTUALLY will always point at the earth and the 2 bulges STOP moving across the moon's surface (there is a torque on the football caused by the earth's gravity that makes it WANT to point to the earth)

(Note that the mass imbalance between the near side and the far side of the moon is also thought to contribute to the tidal locking but NOT entirely. The fact is that the near side now IS heavier than the far side because of a greater frequency of volcanic eruptions on the near side. Those eruptions throw (heavy) basalt onto the moon's surface and create the lunar "seas" on the near side (the huge areas on the moon that look flat from earth). The far side did not have as much volcano activity (it has fewer plains or "seas") and so not as much mass at its surface. Since the near side is heavier, it is attracted more strongly to the earth than the far side.)

This is because the moon is in synchronous rotation with the Earth. It takes exactly the same time to orbit us as it does to spin on its axis once. See the Web Link to the left.

Interesting side note: Because the moon's orbital velocity is not constant due to the eliptical shape of the orbit, while its rotational velocity is constant, an interesting thing called "libration" occurs. Observed carefully over the course of a month or two, the moon will appear to wobble to the left and right. This is east-west libration. There is also a north-south libration related to the inclination of the orbit to our equatorial plane. Combining the effects of these librations over a cycle of about 15 years, a few per cent more that 50% of the moon's surface is actually observable from earth.

Because the moon is tidally locked to the earth, it does in fact rotate on its axis but at the same rate as it orbits the earth (If you think about it it would have to be doing this in order to keep the same face pointing at the earth).

When the moon was first formed it rotated faster than it does now but because it is smaller than the earth the tidal forces cause by the earth gradually slowed it down. Of cause this works the other way too, the moon is slowing the earth and as it does so is receding from the earth. The eventual end state will be for one face of the earth to always face the one face of the moon as it orbits the earth. This end state will not happen for billions of years into the future.

In one theory of the creation of the moon, there was a planet impact (likely Earth and another planet) millions of years ago and the debris kicked up from the immensity of the impact gathered around in the orbit of Earth until it balled to form the moon. It is thought that the reason the moon continually faces Earth is that while the molten rock was cooling, the internal core of the moon was pulled toward the gravitational force of the Earth and cooled in that way, thus holding the face of the moon in our direction via the immense pull of Earth's gravity.

Much like a buoy in the water floats with the heaviest part down, so does the moon against the Earth's gravity with the heaviest spot facing toward us.

Answer 3

Because the Moon rotates on its axis with the same period as it revolves around the Earth. (Mercury does the same with respect to the sun.) This was caused by tidal forces on the Moon from the Earth.

Answer 4

The rotation of the Moon must have gotten slower and slower, due to tidal forces, until it showed us the same side all the time. Many other moons in the Solar System always show their planets the same side; Earth's rotation is also getting slower and slower, until one day in the future we will show the Moon the same side all the time.

Answer 5

All of the stars move; some faster than others. But they are all SO FAR AWAY, that even over the course of a lifetime (or several lifetimes!) nobody could notice the differences. In a thousand years, the constellations in the sky will look a little different; in 10,000 years, they'll look a LOT different.

Answer 6

You only see one face of the moon because it rotates at a speed where the orbit along with rotation keep one side facing Earth. However, there is day and night on both sides of the moon depending on where it is relative to the Sun and Earth.

Answer 7

Yes, but not at the same TIME every night. The Moon rotates like the Earth does, but the rotation is synchronous; it takes the same time as its orbit. So we're always seeing the same side of the Moon.

Answer 8

Pretty much. People who live in rural areas where there are few city lights see far MORE stars than we townfolk do, but the ones that we see are the same ones that a country person does.

Want to see something REALLY impressive? Go wilderness camping. Lay out on a mountaintop at midnight and see the stars as they truly are.

Answer 9

The way the Earth rotates on its axis. It will make you see the same stars until the Axis has changed a significant distance that you will see different stars. That is why you can see Orion more in the fall then in the summer.

Answer 10

Least Common Multiple of Two NumbersThe LCM (least common multiple) is the smallest positive wholenumber exactly divisible by two or more given whole numbers.Example: the LCM of 14 and 35 is 70 because 70/14=5 and70/35=2, and no number smaller than 70 is exactly divisible by 14and 35.The LCM can be calculated as the product of the two numbers dividedby any common factors.In addition, if one number is a multiple of another number, theirLCM is the smaller number.* Method 1To determine the least common multiple of two numbers, determinethe prime factors of both numbers. Then, determine the primefactors they have in common. Multiply the two given numberstogether, and divide by the prime factors they have in common.(Side note: the product of these common prime factors is the twonumbers' "greatest common factor.")Example: Find the least common multiple of 12 and 15.The prime factors of 12 are 2 , 2, and 3 (12 = 2 x 2 x 3)The prime factors of 15 are 3 and 5 (15 = 3 x 5)The only prime factor in common is 3.The least common multiple is (12 x 15) divided by 3. This is 180 /3 = 60The least common multiple is 60.Example: Find the least common multiple of 9 and 11.The prime factors of 9 are 3 and 3.The prime factors of 11 are only 11.There are no prime factors in common.The least common multiple is 9 x 11 = 99.Example: Find the least common multiple of 30 and 42.The prime factors of 30 are 2, 3, and 5.The prime factors of 42 are 2, 3, and 7.The prime factors in common are 2 and 3.The least common multiple is (2 x 3 x 5) x (2 x 3 x 7) / (2 x 3) =210.By representing it as a calculation with prime factors, you cancancel out the divisors, so you have as your reduced calculation 5x 2 x 3 x 7 rather than 30 x 42 ÷ 6.* Method 2You can eliminate large multiplications and divisions bydetermining the common factors, finding their product, thenmultiplying by the non-common factors.Example: Find the least common multiple of 125 and 175,125 = 5 x 5 x 5175 = 5 x 5 x 7Common factors = 5 x 5 = 25Uncommon factors = 5 x 7 = 35 and the LCM is 35 x 25 = 875.* Method 3The LCM can also be found for more complex numbers by taking themultiple of the highest power of prime factors from both numbers.(see section below on three numbers).Example: Find the LCM of 72 and 90 is 360,72 = 2^3 x 3^2 (8 x 9)90 = 2 x 3^2 x 5 (2 x 9 x 5)and 2^3 x 3^2 x 5 = 360Least Common Multiple for Three or More Numbers (ExponentialMethod)(*see the related question below)For more than two numbers, LCM can be found as the product of thehighest power of prime factors from all numbers.For example, the LCM of 28, 98, and 350 is 4900 :28 = 22 x 798 = 2 x 72350 = 2 x 52 x 7and (22 x 52 x 72 = 4 x 25 x 49 = 4900).Least Common Multiple of One NumberThere is no "least common multiple" for a single number, becausethe least common multiple is the smallest multiple that two or morenumbers have in common.For two numbers:First factor each number to its prime factorsNext note the Highest Common FactorNext multiply your two numbersFinally divide that figure by the HCF.EG 24 and 42:24 = 2 x 2 x 3, 42 = 2 x 3 x 7Common factors 2 x 3 ie 624 x 42 = 10081008/6 = 168The LCM of 24 and 42 is 168.