moon's gravity

[kannan krishnaswamy]

Good day sir/madam

It is said that Moon's gravity causes the 'high and low tides' in oceans on Earth. How can the Moon which has only 1/6 th of Earth's gravity (which can not even hold an atmosphere around it ) and is approximately 4 lakhs km away from Earth , influence the water mass on the crust of the Earth?

Thanking you.

[neufer]

Good day sir/madam

It is said that Moon's gravity causes the 'high and low tides' in oceans on Earth. How can the Moon which has only 1/6 th of Earth's gravity (which can not even hold an atmosphere around it ) and is approximately 4 lakhs km away from Earth , influence the water mass on the crust of the Earth?

The lunar tidal acceleration at the Earth's surface along the Moon-Earth axis is about 1.1 × 10⁻⁷ g, while the solar tidal acceleration at the Earth's surface along the Sun-Earth axis is about 0.52 × 10⁻⁷ g, where g is the gravitational acceleration at the Earth's surface.

Earth's Equatorial radius = 6,378,100 m
Lunar tidal acceleration = 1.1 × 10⁻⁷ g
Approximate ocean tidal height = 0.7 m = (6,378,100 m × 1.1 × 10⁻⁷)

[Céline Richard]

Hello

I would like to speak about tides on the Moon. I know this is a shocking way to express myself, because there is no water on the Moon.
However, i was told there was some sort of "tides of rocks", due to the earth gravity. When i sea pictures of the Moon, i can hardly imagine that there are moving rocks, because it seems so quite, so still.
What happens really on the Moon's surface? Do Moon's landscapes keep changing because of the earth gravitationnal attraction?

Have a very nice day!

Céline

Credits (picture): http://littlesun.canalblog.com/images/t-lune.jpg

[neufer]

I would like to speak about tides on the Moon. I know this is a shocking way to express myself, because there is no water on the Moon.
However, i was told there was some sort of "tides of rocks", due to the earth gravity. When i sea pictures of the Moon, i can hardly imagine that there are moving rocks, because it seems so quite, so still.
What happens really on the Moon's surface? Do Moon's landscapes keep changing because of the earth gravitationnal attraction?

The varying tidal force of the earth on the moon (due mostly to the moon's elliptical orbit)
is about 16 times greater than that of the moon on the earth.

The main effect of this will be to heat the moon internally somewhat above what radioactivity alone would do.

<<Tidal working (also known as tidal heating) occurs through the tidal friction processes: orbital and rotational energy are dissipated as heat in the crust of the moons and planets involved. Io, a moon of Jupiter, is the most volcanically active body in the solar system, with no impact craters surviving on its surface. This is because the tidal force of Jupiter deforms Io; the eccentricity of Io's orbit (a consequence of its participation in a Laplace resonance) causes the height of Io's tidal bulge to vary significantly (by up to 100 m) over the course of an orbit; the friction from this tidal flexing then heats up its interior. A similar but weaker process is theorised to have melted the lower layers of the ice surrounding the rocky mantle of Jupiter's next large moon, Europa. Saturn's moon Enceladus is similarly thought to have a liquid water ocean beneath its icy crust. The water vapor geysers which eject material from Enceladus are thought to be powered by friction generated within this moon's shifting ice crust.>>

<<A working title, sometimes called a production title, is the temporary name of a product or project used during its development, usually a film, novel, video game, or music album. Working titles are used primarily for two reasons; the first being that an official title has not yet been decided upon and the working title is being used as a filler for naming purposes, the second being to intentionally disguise the production of a project.

Examples of the former include the film Die Hard with a Vengeance, which was produced under the title Die Hard: New York and the James Bond films, which are commonly produced under titles such as Bond 22 until an official title is decided upon.

Examples of the latter include Star Wars Episode VI: Return of the Jedi, which was produced under the title Blue Harvest, 2009's Star Trek which was produced under the title Corporate Headquarters, and the Batman films Batman Returns, Batman Begins The Dark Knight and The Dark Knight Rises, which were produced under the titles Dictel, The Intimidation Game, Rory's First Kiss and Prey, respectively.

In some cases a working title may ultimately be used as the official title, as in the case of the films Cloverfield, High School Musical, and Snakes on a Plane (at the insistence of leading man, Samuel L. Jackson, who joked that he took the role for the working title alone, after he learnt the title was going to be changed to Pacific Air Flight 121 upon release), the television show The Cleveland Show, and video games Quake II, Spore, Silent Hill Origins and Epic Mickey.

A title ruse is a practice by which a high-profile film or television series is given a fake working title to keep its production a secret, and to prevent price gouging by suppliers, casual theft and undesirable attention. Purchase orders from vendors, outdoor signs, videocassettes and DVD labels will use the cover title of a film.>>

[Céline Richard]

Hello Art,

I would like to thank you for both your comment and wikipedia link.
I find it very interesting, as well as all the other quotations i have read, among those you have posted.
Your next quotation is raising my curiosity Do you want i put a "working title" when i ask a question , or does your quotation convey another meaning? Anyway, i have learnt a new thing, because i didn't know what was a "working title".

<<A working title, sometimes called a production title, is the temporary name of a product or project used during its development, usually a film, novel, video game, or music album. (...) >>

I wish you a very very good day,

Céline

[The Code]

I would like to speak about tides on the Moon. I know this is a shocking way to express myself, because there is no water on the Moon.
However, i was told there was some sort of "tides of rocks", due to the earth gravity. When i sea pictures of the Moon, i can hardly imagine that there are moving rocks, because it seems so quite, so still.
What happens really on the Moon's surface? Do Moon's landscapes keep changing because of the earth gravitationnal attraction?

The varying tidal force of the earth on the moon (due mostly to the moon's elliptical orbit)
is about 16 times greater than that of the moon on the earth.

The main effect of this will be to heat the moon internally somewhat above what radioactivity alone would do.

<<Tidal working (also known as tidal heating) occurs through the tidal friction processes: orbital and rotational energy are dissipated as heat in the crust of the moons and planets involved. Io, a moon of Jupiter, is the most volcanically active body in the solar system, with no impact craters surviving on its surface. This is because the tidal force of Jupiter deforms Io; the eccentricity of Io's orbit (a consequence of its participation in a Laplace resonance) causes the height of Io's tidal bulge to vary significantly (by up to 100 m) over the course of an orbit; the friction from this tidal flexing then heats up its interior. A similar but weaker process is theorised to have melted the lower layers of the ice surrounding the rocky mantle of Jupiter's next large moon, Europa. Saturn's moon Enceladus is similarly thought to have a liquid water ocean beneath its icy crust. The water vapor geysers which eject material from Enceladus are thought to be powered by friction generated within this moon's shifting ice crust.>>

<<A working title, sometimes called a production title, is the temporary name of a product or project used during its development, usually a film, novel, video game, or music album. Working titles are used primarily for two reasons; the first being that an official title has not yet been decided upon and the working title is being used as a filler for naming purposes, the second being to intentionally disguise the production of a project.

Examples of the former include the film Die Hard with a Vengeance, which was produced under the title Die Hard: New York and the James Bond films, which are commonly produced under titles such as Bond 22 until an official title is decided upon.

Examples of the latter include Star Wars Episode VI: Return of the Jedi, which was produced under the title Blue Harvest, 2009's Star Trek which was produced under the title Corporate Headquarters, and the Batman films Batman Returns, Batman Begins The Dark Knight and The Dark Knight Rises, which were produced under the titles Dictel, The Intimidation Game, Rory's First Kiss and Prey, respectively.

In some cases a working title may ultimately be used as the official title, as in the case of the films Cloverfield, High School Musical, and Snakes on a Plane (at the insistence of leading man, Samuel L. Jackson, who joked that he took the role for the working title alone, after he learnt the title was going to be changed to Pacific Air Flight 121 upon release), the television show The Cleveland Show, and video games Quake II, Spore, Silent Hill Origins and Epic Mickey.

A title ruse is a practice by which a high-profile film or television series is given a fake working title to keep its production a secret, and to prevent price gouging by suppliers, casual theft and undesirable attention. Purchase orders from vendors, outdoor signs, videocassettes and DVD labels will use the cover title of a film.>>

Hey Art, Should I take note From Your post ? It quotes: Star Wars Episode VI: Return of the Jedi. Is that not science fiction? Should I take Note Of your Quotes ? Our little tiny Moon Is dead isn't it? Tidal forces Causing heat, extinct on the Moon ? Our Moon Is Cold And Dead ?

tc

[Chris Peterson]

Our little tiny Moon Is dead isn't it? Tidal forces Causing heat, extinct on the Moon ? Our Moon Is Cold And Dead?

What does "dead" mean? The Earth is dead, too.

The Moon is not internally fluid. It is generally considered tectonically inactive. That doesn't mean it doesn't experience tidal heating from its interaction with the Earth, just as the Earth is heated by interaction with the Moon.

[bystander]

The Moon is not internally fluid.

That may not be true.
http://asterisk.apod.com/vie ... hp?t=22514

[Chris Peterson]

The Moon is not internally fluid.

That may not be true.
http://asterisk.apod.com/vie ... hp?t=22514

Maybe. I should have said a fluid mantle, since that's where tectonics are driven from.

[Céline Richard]

Our little tiny Moon Is dead isn't it? Tidal forces Causing heat, extinct on the Moon ? Our Moon Is Cold And Dead?

What does "dead" mean? The Earth is dead, too.

What do you mean by "dead" ?
There is a very controversial hypothesis, taken from http://en.wikipedia.org/wiki/Gaia_hypothesis:

The Gaia hypothesis, Gaia theory or Gaia principle is an ecological hypothesis or theory proposing that the biosphere and the physical components of the Earth (atmosphere, cryosphere, hydrosphere and lithosphere) are closely integrated to form a complex interacting system that maintains the climatic and biogeochemical conditions on Earth in a preferred homeorhesis. Originally proposed by James Lovelock as the earth feedback hypothesis,[1] it was named the Gaia Hypothesis after the Greek primordial goddess of the Earth, at the suggestion of William Golding, Nobel prizewinner in literature and friend and neighbour of Lovelock.[2] The hypothesis is frequently described as viewing the Earth as a single organism

I am not sure to really understand the analogy between the Earth and an organism: maybe it involves to consider life as a self-sustained or self-organized system, but the Earth doesn't reproduce itself...
Or maybe it is due to a personnification of the Earth, which "enables" life on its surface, which doesn't seem scientific, although in this case, i would prefer imagine the Earth is alive instead of thinking it is dead. Indeed, if it is not scientific, we can choose our point of view

Have a very nice day

Céline

[Chris Peterson]

I am not sure to really understand the analogy between the Earth and an organism: maybe it involves to consider life as a self-sustained or self-organized system, but the Earth doesn't reproduce itself...
Or maybe it is due to a personnification of the Earth, which "enables" life on its surface, which doesn't seem scientific, although in this case, i would prefer imagine the Earth is alive instead of thinking it is dead. Indeed, if it is not scientific, we can choose our point of view :)

I'm willing to grant that the Earth's biosphere, atmosphere, and surface geology interact in a way analogous to the functioning of a living organism. But that can probably be said for any sufficiently complex system, and as you note, Earth does not reproduce. In any case, however, we're talking mainly about planetary interiors here (tectonics), and I don't think there's any reasonable way to consider the Earth's interior part of the Gaia system.

People tend to use "dead" in this context to mean geologically inactive. But that's not a binary distinction. The Moon is not very active compared with the Earth, but it does have some activity- probably driven mainly by tides.

[Céline Richard]

I'm willing to grant that the Earth's biosphere, atmosphere, and surface geology interact in a way analogous to the functioning of a living organism. But that can probably be said for any sufficiently complex system, and as you note, Earth does not reproduce. In any case, however, we're talking mainly about planetary interiors here (tectonics), and I don't think there's any reasonable way to consider the Earth's interior part of the Gaia system.

I think there is tectonics, because there is convection's movements inside the mantle. There are currents (associated to different temperatures) inside the ocean, which circulation partly depends on tectonics. Climate is closely linked to the oceanic circulation.
So i would rather think the interior of the Earth participates to the complex system outside, made of the interactions between biosphere, atmosphere, hydrosphere, litosphere and cryosphere.
However, i don't know if i can extend the analogy between the Earth and the Gaïa hypothesis further, because it depends on the definition of life.

People tend to use "dead" in this context to mean geologically inactive. But that's not a binary distinction. The Moon is not very active compared with the Earth, but it does have some activity- probably driven mainly by tides.

Yes, "geologically inactive", i will remember this definition.

I still wonder what does it look like on the Moon's surface : is there very slow tides of melted rocks ? Or just still landscape ?

Thank you for all your informations,

Céline

[Chris Peterson]

I still wonder what does it look like on the Moon's surface : is there very slow tides of melted rocks ? Or just still landscape ?

Distortion of the lunar interior from tidal forces is not great enough to produce melting. You could not observe the effects of tides on the Moon without instrumentation.

[Céline Richard]

Thank you a lot Chris

Céline

[dougettinger]

Good day sir/madam

The lunar tidal acceleration at the Earth's surface along the Moon-Earth axis is about 1.1 × 10⁻⁷ g, while the solar tidal acceleration at the Earth's surface along the Sun-Earth axis is about 0.52 × 10⁻⁷ g, where g is the gravitational acceleration at the Earth's surface.

Earth's Equatorial radius = 6,378,100 m
Lunar tidal acceleration = 1.1 × 10⁻⁷ g
Approximate ocean tidal height = 0.7 m = (6,378,100 m × 1.1 × 10⁻⁷)

Hello Neufer,

You have stumped me. What equations are behind the scenes in multiplying lunar tidal acceleration by the earth's radius to determine an approximate ocean tide ?

While we are on the topics of an interacting gravity system and equations, is there a way to approximate how much time was needed for the tidal forces between Earth and Moon to lock the Moon's rotation so it faces Earth with the same side ? Of course, the values for the initial rotating velocities would be unknown or "x" for the Moon and "y" for the Earth.


Doug Ettinger
Pittsburgh, PA

[neufer]

Good day sir/madam

The lunar tidal acceleration at the Earth's surface along the Moon-Earth axis is about 1.1 × 10⁻⁷ g, while the solar tidal acceleration at the Earth's surface along the Sun-Earth axis is about 0.52 × 10⁻⁷ g, where g is the gravitational acceleration at the Earth's surface.

Earth's Equatorial radius = 6,378,100 m
Lunar tidal acceleration = 1.1 × 10⁻⁷ g
Approximate ocean tidal height = 0.7 m = (6,378,100 m × 1.1 × 10⁻⁷)

You have stumped me.
What equations are behind the scenes in multiplying lunar tidal acceleration by the earth's radius to determine an approximate ocean tide ?

The weight of a 6,378,100 m column of water with no moon above it is equal
to the weight of a 6,378,100.7 m column of water with a moon above it.

While we are on the topics of an interacting gravity system and equations, is there a way to approximate how much time was needed for the tidal forces between Earth and Moon to lock the Moon's rotation so it faces Earth with the same side ? Of course, the values for the initial rotating velocities would be unknown or "x" for the Moon and "y" for the Earth.

<<An estimate of the time for a body to become tidally locked can be obtained using the following formula:


where is the semi-major axis of the motion of the satellite around the planet
and R is the radius of the satellite (with masses in kg, distances in meters).

Note the extremely strong dependence on orbital radius .

(The rigidity of the satellite μ can be roughly taken as:

• 3×10¹⁰ (Nm⁻²) for rocky objects and
  4×10⁹ Nm⁻² for icy ones.)

A large moon will lock faster than a smaller moon at the same orbital radius from the planet because , grows much faster with satellite radius than R. A possible example of this is in the Saturn system, where Hyperion is not tidally locked, while the larger Iapetus, which orbits at a greater distance, is. It must be noted, however, that this is not clear cut because Hyperion also experiences strong driving from the nearby Titan, which forces its rotation to be chaotic.>>

[dougettinger]

Thanks, Art, for this exciting equation for locking a satellite orbiting a planet. Common sense would lead me to believe that the initial rotation speed of the satellite is a definite factor, but it is not in the equation.

I still do not understand your explanation about the moon's tidal acceleration. You are probably using some ratio concerning W = mg ?

Doug Ettinger

[Chris Peterson]

Thanks, Art, for this exciting equation for locking a satellite orbiting a planet. Common sense would lead me to believe that the initial rotation speed of the satellite is a definite factor, but it is not in the equation.

FWIW, we do not need to rely on theory alone when considering the Moon. The tidal interaction between the Earth and Moon changed the rotation rate of the Earth as well as the distance between the two bodies. Both of these are seen in the geological record, so the actual history of tidal momentum transfer between the two bodies can be inferred from measurements.

[dougettinger]

My question is about the equation. Why are not the initial rotations considered since angular momentum must be transferred?

My new question is how they can infer original distance between the Earth and Moon and possible slow down by measurements in the geological records?

Doug Ettinger

[neufer]

My question is about the equation. Why are not the initial rotations considered since angular momentum must be transferred?

The time depends only linearly on the initial spin rate so a crude guess works pretty good.

<<It is sensible to guess one revolution every 12 hours in the initial non-locked state
(most asteroids have rotational periods between about 2 hours and about 2 days)>>

My new question is how they can infer original distance between the Earth and Moon and possible slow down by measurements in the geological records?

<<Studies of growth in fossil corals have made a fascinating contribution to geochronology involving past ocean tides and the inferred relationship between the earth and the moon. The moon pulls ocean water in a tidal bulge which moves westward as the earth rotates toward the east. The tidal drag acts as a brake on the spinning earth, gradually slowing it down. Early in the eighteenth century, Edmund Halley, Astronomer Royal of England, noted that there was a discrepancy between the recorded locations of ancient eclipses of the moon and their predicted places of observation. He pointed out that the differences could be resolved by assuming a slowing down of the rate of rotation of the earth. Modern astronomers have confirmed his theory, and by precise methods have found that the earth is now slowing at the rate of 0.002 seconds per century. This seems very little, but can be appreciable over tens of millions of years.

The slowing of the earth's spin decreases the number of days in the year and causes the moon to draw away from the earth, thus conserving the [angular momentum] within the earth-moon system. The rate of recession of the moon away from the earth is now calculated at about [3.8] centimeters per year. Until recently there was no way to test these astronomical deductions, but paleontology now provides an independent test.

The discovery was made by John W. Wells at Cornell University, a leading investigator of living and fossil corals. Wells knew that the skeletons of corals (and many other kinds of invertebrates) display parallel growth rings similar to the annual growth of trees. He was able to show that annual bands of living corals are themselves made of narrow lines which closely correspond to one day's growth. With his fossil corals, he reported in 1963 that specimens of Devonian age averaged about 400 lines per year, and Carboniferous corals about 380. Subsequent investigations by intrigued paleontologists have shown that the number of daily growth increments per year in corals and molluscs has indeed been decreasing through geological time. Astronomers had already calculated that average tidal friction would allow 425 days per year in the Cambrian and 400 days per year for the Devonian. As well as providing evidence of close agreement between these two scientific approaches, John Wells' work also provides a measure of the antiquity of fossils in years, totally independent of radiometric methods.

Following up Wells' discovery, Colin T. Scrutton, of the British Museum (Natural History), found what appeared to be monthly bands in Devonian corals equivalent to the intervals between times of the full moon. He calculated 13.03 lunar months in a Devonian year of 399 days. This work has opened up a whole new field of historical research involving the earth-moon relationship.>>

The variation of length of day versus geological time

---

The Length of the Day: A Cosmological Perspective
Volume 1 PROGRESS IN PHYSICS January, 2009
Arbab I. Arbab, Department of Physics, Faculty of Science, University of Khartoum

We have found an empirical law for the variation of the length of the Earth’s day with geologic time employing Wells’s data. We attribute the lengthening of the Earth’s day to the present cosmic expansion of the Universe. The prediction of law has been found to be in agreement with the astronomical and geological data.

The length of the day is found to be 6 hours when the Earth formed.

[Chris Peterson]

My new question is how they can infer original distance between the Earth and Moon and possible slow down by measurements in the geological records?

The Earth's rotation rate shows up because both annual and diurnal effects are visible in sediments, which become sedimentary rock. For instance, diatoms and other life forms settle on the ocean floor at different rates day and night, and this can be seen is some preserved sediments. There are annual variations as well- seasonal changes in how the sediment forms. You can identify the period of the annual pattern, count the diurnal pattern, and that tells you how many days are in a year. Since the length of the year has not changed, what this really gives you is the length of the day (the Earth used to spin much faster than now). Also present in sediments are variations caused by tides. From this, it is possible to reconstruct the orbit period of the Moon around the Earth. Since both bodies have stable masses, this can be used to calculate the distance between the two.

Sedimentary rock is the best proxy for this information, but there are others as well: coral growth, some cave structures, some fossilized shells- basically, all things that have periodic structure related to the day, year, or tides.

The changing distance from the Earth to the Moon and the change in day length as measured in the geological record are beautifully in agreement with the tidal angular momentum calculations.

[dougettinger]

The initial length of Earth's day and the time for t(lock) is very exciting news for me. Somehow this information has escaped me through the years. Then all I yet need to know is "a", the semi-major axis of rotation in the beginning, and/or the initial distance between the Moon and Earth as computed by angular momentum equations. Does anyone know what these values are?

I am still trying to make sense of Neufer's computation of "approximate ocean tidal height = 0.7 m = 6.378,100 m x 1.1 x 10 (-7). If h(2) = h(1) x g(1)/g(2), how does g(1)/g(2) = 1.1 x 10 (-7) ?

Doug Ettinger
Pittsburgh, PA
01/27/2011

[dougettinger]

I believe the ratios of the heights and the gravity accelerations above each column are equal. Hence, h(2)/h(1) = g(2)/g(1) and then h(2) = h(1) x g(2)/g(1). Numerically, 0.7 m = 6,378,100 m x 1.1 x 10(-7).

Doug Ettinger, Pittsburgh, PA 01/27/11