Name one or more favorite scientific facts! - Page 21

Thor 2 · 12th November 2019, 01:29 PM

As I am sure most here know, the Moon's spin matches its orbital rotation. This being why we always see the same side of the Moon from Earth - with a slight variation due to the elliptical orbit of the Moon.

How many know why this is so?

arthwollipot · 12th November 2019, 05:20 PM

Spiders are not crabs, and crabs are not spiders, but there are both spider crabs and crab spiders.

arthwollipot · 12th November 2019, 05:22 PM

Originally Posted by Thor 2

As I am sure most here know, the Moon's spin matches its orbital rotation. This being why we always see the same side of the Moon from Earth - with a slight variation due to the elliptical orbit of the Moon.

How many know why this is so?

I do. I'm not sure I could explain it technically, but there are several bodies in the solar system that are tidally locked with their parent.

Roboramma · 12th November 2019, 06:57 PM

Originally Posted by arthwollipot

I do. I'm not sure I could explain it technically, but there are several bodies in the solar system that are tidally locked with their parent.

I managed to give a good enough explanation of the mechanism of tidal locking to my girlfriend on the fly that she was able to understand how it works, but I suspect if I tried to do it here there'd be more errors than I'm happy to expose.

Out of curiosity, which bodies are tidally locked? The Moon, obivously, but that's the only one I know. Are Phobos and Demos tidally locked? Mercury is partially locked, or something, but that's something I don't fully understand, I think it goes through 2 days / 3 orbits? Something like that...

I'm guessing the other tidally locked bodies are moons, I just don't know which ones they would be offhand...

arthwollipot · 12th November 2019, 08:09 PM

Originally Posted by Roboramma

I managed to give a good enough explanation of the mechanism of tidal locking to my girlfriend on the fly that she was able to understand how it works, but I suspect if I tried to do it here there'd be more errors than I'm happy to expose.

Out of curiosity, which bodies are tidally locked? The Moon, obivously, but that's the only one I know. Are Phobos and Demos tidally locked? Mercury is partially locked, or something, but that's something I don't fully understand, I think it goes through 2 days / 3 orbits? Something like that...

I'm guessing the other tidally locked bodies are moons, I just don't know which ones they would be offhand...

I had to look it up, but according to Wikipedia, most major moons are tidally locked to their primaries. I thought it was only a few. Pluto and Charon are tidally locked to each other.

Ziggurat · 12th November 2019, 08:19 PM

Originally Posted by arthwollipot

Spiders are not crabs, and crabs are not spiders, but there are both spider crabs and crab spiders.

A red giant panda is different than a giant red panda.

Gord_in_Toronto · 12th November 2019, 08:22 PM

Once upon a time (in some of my older Astronomy books), Mercury was thought to be tidally locked with the Sun. Now it is known not to be. The resonance between its rotation and revolution is interesting.

RecoveringYuppy · 12th November 2019, 08:27 PM

Originally Posted by Gord_in_Toronto

Once upon a time (in some of my older Astronomy books), Mercury was thought to be tidally locked with the Sun. Now it is known not to be.

Source please?

ETA: This might be partially a semantic issue? Seems to be some disagreement over whether tidally influenced resonances aren't examples of tidal locking, or whether tidal locking strictly means rotation=revolution.

arthwollipot · 12th November 2019, 08:36 PM

Originally Posted by RecoveringYuppy

Source please?

Wikipedia, same link as above.

Quote:

It was thought for some time that Mercury was in synchronous rotation with the Sun. This was because whenever Mercury was best placed for observation, the same side faced inward. Radar observations in 1965 demonstrated instead that Mercury has a 3:2 spin–orbit resonance, rotating three times for every two revolutions around the Sun, which results in the same positioning at those observation points. Modeling has demonstrated that Mercury was captured into the 3:2 spin–orbit state very early in its history, within 20 (and more likely even 10) million years after its formation.[16]

Footnote 16 leads to:

Quote:

Noyelles, Benoit; Frouard, Julien; Makarov, Valeri V. & Efroimsky, Michael (2014). "Spin–orbit evolution of Mercury revisited". Icarus. 241: 26–44. arXiv:1307.0136. Bibcode:2014Icar..241...26N. doi10.1016/j.icarus.2014.05.045.

RecoveringYuppy · 12th November 2019, 08:55 PM

Yes, but note that what you quote doesn't mention tidal locking.

arthwollipot · 12th November 2019, 10:33 PM

Originally Posted by RecoveringYuppy

Yes, but note that what you quote doesn't mention tidal locking.

It mentions synchronous rotation, which is basically the same thing. Pluto and Charon are in synchronous rotation, which means that they're tidally locked to each other.

RecoveringYuppy · 13th November 2019, 06:59 AM

Originally Posted by arthwollipot

It mentions synchronous rotation, which is basically the same thing. Pluto and Charon are in synchronous rotation, which means that they're tidally locked to each other.

But that's not at issue. Here is what I was commenting on:

Originally Posted by Gord_in_Toronto

Once upon a time (in some of my older Astronomy books), Mercury was thought to be tidally locked with the Sun. Now it is known not to be. The resonance between its rotation and revolution is interesting.

That's not correct based on the wikipedia article. The accurate way to say what I think Gord is referring to is: Mercury was once thought to be in synchronous rotation with the Sun via tidal locking, now it is known not to be in synchronous rotation but, rather, tidal locking has caused it to be in a resonance.

IOW Resonances are due to tidal locking and synchronous orbit is a special case of resonance.

pgwenthold · 13th November 2019, 07:14 AM

Originally Posted by Thor 2

As I am sure most here know, the Moon's spin matches its orbital rotation. This being why we always see the same side of the Moon from Earth - with a slight variation due to the elliptical orbit of the Moon.

This leads to one of my favorite facts. Because of this, if you are on the moon, the earth does not rise and set like the moon does from the earth. In fact, the earth pretty much stays in the same place in the sky.

In order to see the "earth rise" you have to be orbiting the moon. That's the picture Bill Anders took from Apollo 8

RecoveringYuppy · 13th November 2019, 07:19 AM

One of my favorite facts is that the so called dark side of the Moon gets a bit more light than the other side. I name this fact Roger.

xterra · 13th November 2019, 08:56 AM

The following URL links to "The Atheist Experience" for November 10, 2019.

https://youtu.be/xzjcUXJcjps?t=4664

From this point to the end of the show is about 34 minutes of some incredible examples of non-science.

Gord_in_Toronto · 13th November 2019, 10:26 AM

Originally Posted by RecoveringYuppy

Source please?

ETA: This might be partially a semantic issue? Seems to be some disagreement over whether tidally influenced resonances aren't examples of tidal locking, or whether tidal locking strictly means rotation=revolution.

No can (easily) do as all my astronomy books are in storage but this article does discuss the subject:

https://scienceblogs.com/startswitha...ery-of-mercury

Gord_in_Toronto · 13th November 2019, 10:28 AM

Originally Posted by RecoveringYuppy

But that's not at issue. Here is what I was commenting on:

That's not correct based on the wikipedia article. The accurate way to say what I think Gord is referring to is: Mercury was once thought to be in synchronous rotation with the Sun via tidal locking, now it is known not to be in synchronous rotation but, rather, tidal locking has caused it to be in a resonance.

IOW Resonances are due to tidal locking and synchronous orbit is a special case of resonance.

Umm. Yes. That's exactly what I meant.

alfaniner · 13th November 2019, 11:34 AM

Originally Posted by RecoveringYuppy

One of my favorite facts is that the so called dark side of the Moon gets a bit more light than the other side. I name this fact Roger.

I'm not sure if you're being facetious here. One can never tell on these boards.

RecoveringYuppy · 13th November 2019, 11:36 AM

Originally Posted by alfaniner

I'm not sure if you're being facetious here. One can never tell on these boards.

The fact is true. In fact, it's true with either the correct definition of "dark side" (where it's trivially true) or the erroneous confusion with "far side" (where it's true to distance to Sun and effect of eclipses).

sphenisc · 13th November 2019, 02:49 PM

Originally Posted by RecoveringYuppy

The fact is true. In fact, it's true with either the correct definition of "dark side" (where it's trivially true) or the erroneous confusion with "far side" (where it's true to distance to Sun and effect of eclipses).

I think, using the correct definition, the light side of the moon gets more light than the dark side does.

RecoveringYuppy · 13th November 2019, 02:57 PM

Originally Posted by sphenisc

I think, using the correct definition, the light side of the moon gets more light than the dark side does.

Oh, duh, I should have re-read my original claim. You are of course correct. What I said only applies to the "so called dark side" as I originally stated.

JeanTate · 13th November 2019, 03:04 PM

Originally Posted by Thor 2

As I am sure most here know, the Moon's spin matches its orbital rotation. This being why we always see the same side of the Moon from Earth - with a slight variation due to the elliptical orbit of the Moon.

How many know why this is so?

There are some other cool facts.

Such as the 24-hour Earth affects the 28-day Moon via tides ... 24 is increasing (what is 28 doing?). So the cosmic coincidence that the Moon is ~the same size (on the sky) as the Sun is rather narrow (in geological time). Once the Moon was much closer (and tides were much bigger). And astronomical models of the Earth-Moon system match geological evidence going back almost to the earliest sedementary deposits. How can geologists estimate the number of days in a year, in a ~billion year old rock formation?

Thor 2 · 13th November 2019, 04:29 PM

Originally Posted by arthwollipot

I do. I'm not sure I could explain it technically, but there are several bodies in the solar system that are tidally locked with their parent.

The term "tidal locking" has been used by some posters above but I haven't seen an explanation of how this works here. I read about it some time ago but can't find the explanation in an article again. I gained a fairly good grasp I think from my previous reading so here it is in my words:

In the earlier days of the Moon's existence it was molten to a larger degree than today.

The Moon would have had a faster speed of rotation than the current 28 days in the same direction as today (I think most orbiting bodies rotate in the same direction as the orbit) and as it rotated and being molten distorted due to Earths gravitational pull. We can refer to this molten flow as tidal.

Distortion requires energy and that energy was taped from the rotational kinetic energy, causing the Moon's spin to slow down. Toward the end I imagine it would have maybe rocked back and forth, until its spin was in sync with the orbit.

ceptimus · 13th November 2019, 05:13 PM

I remember a long ongoing argument, maybe it was on this board, about whether the moon revolves with respect to the earth. One group argued that it did rotate, once per orbit, and the other group argued that with respect to the earth it didn't rotate - because if it did, we'd be able to see the other side.

Both groups understood exactly what was happening, but they couldn't agree about how to correctly describe it, in English.

ceptimus · 13th November 2019, 05:21 PM

I remember someone used the analogy of a squirrel hiding, clinging on the opposite side of a tree trunk compared to where you're standing. As you walk around the tree, the squirrel moves too, so as to remain hidden, but it always faces towards you.

After you've walked one complete circuit of the tree, the question then is, have you walked around the squirrel?

Delvo · 13th November 2019, 05:48 PM

It isn't quite completely locked. Its average orientation is locked, but it drifts minutely above and below, or ahead of and behind, that average. So the amount of its surface that can be seen from different parts Earth at different times is actually not half but almost three fifths.

One part of the reason for that is actually a cheat, meaning by itself it doesn't mean the moon isn't tidally locked; it's just a matter of perception from Earth's surface making it look not quite so if one's observations are precise enough. It would still apply even if the "lock" were more all-encompassing and the following two phenomena after this paragraph didn't happen. It's that the moon can be simultaneously observed by different points on Earth at the same time that are up to roughly one Earth-diameter apart from each other. That sets up a stereoscopic effect by which you could see small differences if you compared simultaneously-shot images of it from far-flung points on Earth. It also means that you could observe a small amount of apparent rotation of the moon form a fixed point on Earth over the course of a single day/night as you moved from a moonrise point of view to a moonset point of view. Even if the following two things weren't real, this would still be the case.

But also, there are two ways in which the moon is not perfectly locked.

First, its axis of rotation is tilted, not perpendicular to the plane of its orbit. The geometric effect is exactly the same as with the angle of Earth's axis to Earth's plane or orbit, which causes the sun to "see" more of Earth's northern hemisphere during the northern summer and more of the southern hemisphere during the southern summer. We see more of the moon's northern hemisphere during one half of its orbit and more of its southern hemisphere during the other half.

And second, while its speed of rotation and speed of movement along its orbital path match each other on average, the latter fluctuates more. In a non-circular orbit, the orbiting object moves slower (both in miles per time and in degrees per time as seen from the object it's orbiting) when it's farther away and faster (again both in miles per time and in degrees per time as seen from the object it's orbiting) when it's closer. Thus, the net effect of a constant rotation rate and an overall averaged-out 1:1 ratio of rotations to orbits combines to a small net forward (eastward) rotation near apogee and a small net backward (westward) rotation near perigee. Another way to look at the same thing is that if it's rotating once for each trip along an ellipse then the same face is always facing the point exactly halfway between the ellipse's two epicenters, which is not the same as always facing either epicenter, which is where the orbited object is; instead it means facing slightly back behind the nearest epicenter as it approaches one end of its orbit, and facing slightly ahead of the nearest epicenter as it moves away from that end of its orbit.

An observer holding position in space between Earth and the moon, to always look straight at the moon and keep Earth at his/her back (thus eliminating any misleading or distracting effects that are caused by Earth's rotation & atmosphere alone) would see the moon doing this each "month" (moonth?):

Image linked instead of embedded, to avoid having the host's server need to serve it whenever this page loads

Notice the word "libration" in the link. That's the word to look up for more about this elsewhere.

arthwollipot · 13th November 2019, 06:09 PM

Originally Posted by ceptimus

I remember a long ongoing argument, maybe it was on this board, about whether the moon revolves with respect to the earth. One group argued that it did rotate, once per orbit, and the other group argued that with respect to the earth it didn't rotate - because if it did, we'd be able to see the other side.

Both groups understood exactly what was happening, but they couldn't agree about how to correctly describe it, in English.

And that's clearly the only time that has ever happened.

sphenisc · 13th November 2019, 06:12 PM

Originally Posted by ceptimus

I remember someone used the analogy of a squirrel hiding, clinging on the opposite side of a tree trunk compared to where you're standing. As you walk around the tree, the squirrel moves too, so as to remain hidden, but it always faces towards you.

After you've walked one complete circuit of the tree, the question then is, have you walked around the squirrel?

https://www.imaginativeuniversal.com...-the-squirrel/

Cheetah · 14th November 2019, 02:05 AM

What a ridiculously biased, self centered, conclusion that is. Totally and disgustingly speciest.
Obviously it's the squirrel walking around the human, or not, depending on the squirrels definition of 'around'.

Gord_in_Toronto · 14th November 2019, 07:13 AM

Originally Posted by Cheetah

What a ridiculously biased, self centered, conclusion that is. Totally and disgustingly speciest.
Obviously it's the squirrel walking around the human, or not, depending on the squirrels definition of 'around'.

Please let's not go there again. It will not end well.

To quote the bowl of petunias: "Oh no, not again!"

Originally Posted by Douglas Adams, The Hitchhiker's Guide to the Galaxy

And wow! Hey! What’s this thing suddenly coming towards me very fast? Very very fast. So big and flat and round, it needs a big wide sounding name like … ow … ound … round … ground! That’s it! That’s a good name – ground!

I wonder if it will be friends with me?

And the rest, after a sudden wet thud, was silence.

Curiously enough, the only thing that went through the mind of the bowl of petunias as it fell was Oh no, not again. Many people have speculated that if we knew exactly why the bowl of petunias had thought that we would know a lot more about the nature of the universe than we do now.”

Dr. Keith · 14th November 2019, 11:10 AM

Originally Posted by sphenisc

https://www.imaginativeuniversal.com...-the-squirrel/

The real joy of that is in the comments.

bruto · 15th November 2019, 04:23 PM

Originally Posted by GlennB

I studied physics at school, but then there were quite a lot of them. Only one biology and chemistry though

But a single bit of biology or chemistry would not put you out of action like a single dose of physic.

12th November 2019, 01:29 PM	#801
Thor 2 Philosopher Join Date: May 2016 Location: Brisbane, Aust. Posts: 6,509	As I am sure most here know, the Moon's spin matches its orbital rotation. This being why we always see the same side of the Moon from Earth - with a slight variation due to the elliptical orbit of the Moon. How many know why this is so?
	__________________ Thinking is a faith hazard.

12th November 2019, 05:20 PM	#802
arthwollipot Observer of Phenomena Pronouns: he/him Join Date: Feb 2005 Location: Ngunnawal Country Posts: 69,572	Spiders are not crabs, and crabs are not spiders, but there are both spider crabs and crab spiders.
	__________________ Please scream inside your heart.

12th November 2019, 05:22 PM	#803
arthwollipot Observer of Phenomena Pronouns: he/him Join Date: Feb 2005 Location: Ngunnawal Country Posts: 69,572	Originally Posted by Thor 2 As I am sure most here know, the Moon's spin matches its orbital rotation. This being why we always see the same side of the Moon from Earth - with a slight variation due to the elliptical orbit of the Moon. How many know why this is so? I do. I'm not sure I could explain it technically, but there are several bodies in the solar system that are tidally locked with their parent.
	__________________ Please scream inside your heart.

12th November 2019, 06:57 PM	#804
Roboramma Penultimate Amazing Join Date: Feb 2005 Location: Shanghai Posts: 14,143	Originally Posted by arthwollipot I do. I'm not sure I could explain it technically, but there are several bodies in the solar system that are tidally locked with their parent. I managed to give a good enough explanation of the mechanism of tidal locking to my girlfriend on the fly that she was able to understand how it works, but I suspect if I tried to do it here there'd be more errors than I'm happy to expose. Out of curiosity, which bodies are tidally locked? The Moon, obivously, but that's the only one I know. Are Phobos and Demos tidally locked? Mercury is partially locked, or something, but that's something I don't fully understand, I think it goes through 2 days / 3 orbits? Something like that... I'm guessing the other tidally locked bodies are moons, I just don't know which ones they would be offhand...
	__________________ "... when people thought the Earth was flat, they were wrong. When people thought the Earth was spherical they were wrong. But if you think that thinking the Earth is spherical is just as wrong as thinking the Earth is flat, then your view is wronger than both of them put together." Isaac Asimov

12th November 2019, 08:09 PM	#805
arthwollipot Observer of Phenomena Pronouns: he/him Join Date: Feb 2005 Location: Ngunnawal Country Posts: 69,572	Originally Posted by Roboramma I managed to give a good enough explanation of the mechanism of tidal locking to my girlfriend on the fly that she was able to understand how it works, but I suspect if I tried to do it here there'd be more errors than I'm happy to expose. Out of curiosity, which bodies are tidally locked? The Moon, obivously, but that's the only one I know. Are Phobos and Demos tidally locked? Mercury is partially locked, or something, but that's something I don't fully understand, I think it goes through 2 days / 3 orbits? Something like that... I'm guessing the other tidally locked bodies are moons, I just don't know which ones they would be offhand... I had to look it up, but according to Wikipedia, most major moons are tidally locked to their primaries. I thought it was only a few. Pluto and Charon are tidally locked to each other.
	__________________ Please scream inside your heart.

12th November 2019, 08:19 PM	#806
Ziggurat Penultimate Amazing Join Date: Jun 2003 Posts: 47,953	Originally Posted by arthwollipot Spiders are not crabs, and crabs are not spiders, but there are both spider crabs and crab spiders. A red giant panda is different than a giant red panda.
	__________________ "As long as it is admitted that the law may be diverted from its true purpose -- that it may violate property instead of protecting it -- then everyone will want to participate in making the law, either to protect himself against plunder or to use it for plunder. Political questions will always be prejudicial, dominant, and all-absorbing. There will be fighting at the door of the Legislative Palace, and the struggle within will be no less furious." - Bastiat, The Law

12th November 2019, 08:22 PM	#807
Gord_in_Toronto Penultimate Amazing Join Date: Jul 2006 Posts: 20,141	Once upon a time (in some of my older Astronomy books), Mercury was thought to be tidally locked with the Sun. Now it is known not to be. The resonance between its rotation and revolution is interesting.
	__________________ "Reality is what's left when you cease to believe." Philip K. Dick

12th November 2019, 08:27 PM	#808
RecoveringYuppy Penultimate Amazing Join Date: Nov 2006 Posts: 10,346	Originally Posted by Gord_in_Toronto Once upon a time (in some of my older Astronomy books), Mercury was thought to be tidally locked with the Sun. Now it is known not to be. Source please? ETA: This might be partially a semantic issue? Seems to be some disagreement over whether tidally influenced resonances aren't examples of tidal locking, or whether tidal locking strictly means rotation=revolution.
	Last edited by RecoveringYuppy; 12th November 2019 at 08:32 PM.

12th November 2019, 08:36 PM	#809
arthwollipot Observer of Phenomena Pronouns: he/him Join Date: Feb 2005 Location: Ngunnawal Country Posts: 69,572	Originally Posted by RecoveringYuppy Source please? Wikipedia, same link as above. Quote: It was thought for some time that Mercury was in synchronous rotation with the Sun. This was because whenever Mercury was best placed for observation, the same side faced inward. Radar observations in 1965 demonstrated instead that Mercury has a 3:2 spin–orbit resonance, rotating three times for every two revolutions around the Sun, which results in the same positioning at those observation points. Modeling has demonstrated that Mercury was captured into the 3:2 spin–orbit state very early in its history, within 20 (and more likely even 10) million years after its formation.[16] Footnote 16 leads to: Quote: Noyelles, Benoit; Frouard, Julien; Makarov, Valeri V. & Efroimsky, Michael (2014). "Spin–orbit evolution of Mercury revisited". Icarus. 241: 26–44. arXiv:1307.0136. Bibcode:2014Icar..241...26N. doi10.1016/j.icarus.2014.05.045.
	__________________ Please scream inside your heart.

12th November 2019, 08:55 PM	#810
RecoveringYuppy Penultimate Amazing Join Date: Nov 2006 Posts: 10,346	Yes, but note that what you quote doesn't mention tidal locking.

12th November 2019, 10:33 PM	#811
arthwollipot Observer of Phenomena Pronouns: he/him Join Date: Feb 2005 Location: Ngunnawal Country Posts: 69,572	Originally Posted by RecoveringYuppy Yes, but note that what you quote doesn't mention tidal locking. It mentions synchronous rotation, which is basically the same thing. Pluto and Charon are in synchronous rotation, which means that they're tidally locked to each other.
	__________________ Please scream inside your heart. Last edited by arthwollipot; 12th November 2019 at 10:34 PM.

13th November 2019, 06:59 AM	#812
RecoveringYuppy Penultimate Amazing Join Date: Nov 2006 Posts: 10,346	Originally Posted by arthwollipot It mentions synchronous rotation, which is basically the same thing. Pluto and Charon are in synchronous rotation, which means that they're tidally locked to each other. But that's not at issue. Here is what I was commenting on: Originally Posted by Gord_in_Toronto Once upon a time (in some of my older Astronomy books), Mercury was thought to be tidally locked with the Sun. Now it is known not to be. The resonance between its rotation and revolution is interesting. That's not correct based on the wikipedia article. The accurate way to say what I think Gord is referring to is: Mercury was once thought to be in synchronous rotation with the Sun via tidal locking, now it is known not to be in synchronous rotation but, rather, tidal locking has caused it to be in a resonance. IOW Resonances are due to tidal locking and synchronous orbit is a special case of resonance.
	Last edited by RecoveringYuppy; 13th November 2019 at 07:02 AM.

13th November 2019, 07:14 AM	#813
pgwenthold Penultimate Amazing Join Date: Sep 2001 Posts: 20,052	Originally Posted by Thor 2 As I am sure most here know, the Moon's spin matches its orbital rotation. This being why we always see the same side of the Moon from Earth - with a slight variation due to the elliptical orbit of the Moon. This leads to one of my favorite facts. Because of this, if you are on the moon, the earth does not rise and set like the moon does from the earth. In fact, the earth pretty much stays in the same place in the sky. In order to see the "earth rise" you have to be orbiting the moon. That's the picture Bill Anders took from Apollo 8
	__________________ "As your friend, I have to be honest with you: I don't care about you or your problems" - Chloe, Secret Life of Pets

13th November 2019, 07:19 AM	#814
RecoveringYuppy Penultimate Amazing Join Date: Nov 2006 Posts: 10,346	One of my favorite facts is that the so called dark side of the Moon gets a bit more light than the other side. I name this fact Roger.
	Last edited by RecoveringYuppy; 13th November 2019 at 07:24 AM.

13th November 2019, 08:56 AM	#815
xterra So far, so good... Join Date: Apr 2012 Location: On the outskirts of Nowhere; the middle was too crowded Posts: 3,698	A different view The following URL links to "The Atheist Experience" for November 10, 2019. https://youtu.be/xzjcUXJcjps?t=4664 From this point to the end of the show is about 34 minutes of some incredible examples of non-science.
	__________________ Over we go....

13th November 2019, 10:26 AM	#816
Gord_in_Toronto Penultimate Amazing Join Date: Jul 2006 Posts: 20,141	Originally Posted by RecoveringYuppy Source please? ETA: This might be partially a semantic issue? Seems to be some disagreement over whether tidally influenced resonances aren't examples of tidal locking, or whether tidal locking strictly means rotation=revolution. No can (easily) do as all my astronomy books are in storage but this article does discuss the subject: https://scienceblogs.com/startswitha...ery-of-mercury
	__________________ "Reality is what's left when you cease to believe." Philip K. Dick

13th November 2019, 10:28 AM	#817
Gord_in_Toronto Penultimate Amazing Join Date: Jul 2006 Posts: 20,141	Originally Posted by RecoveringYuppy But that's not at issue. Here is what I was commenting on: That's not correct based on the wikipedia article. The accurate way to say what I think Gord is referring to is: Mercury was once thought to be in synchronous rotation with the Sun via tidal locking, now it is known not to be in synchronous rotation but, rather, tidal locking has caused it to be in a resonance. IOW Resonances are due to tidal locking and synchronous orbit is a special case of resonance. Umm. Yes. That's exactly what I meant.
	__________________ "Reality is what's left when you cease to believe." Philip K. Dick

13th November 2019, 11:34 AM	#818
alfaniner Penultimate Amazing Join Date: Aug 2001 Posts: 24,580	Originally Posted by RecoveringYuppy One of my favorite facts is that the so called dark side of the Moon gets a bit more light than the other side. I name this fact Roger. I'm not sure if you're being facetious here. One can never tell on these boards.
	__________________ Science is self-correcting. Woo is self-contradicting.

13th November 2019, 11:36 AM	#819
RecoveringYuppy Penultimate Amazing Join Date: Nov 2006 Posts: 10,346	Originally Posted by alfaniner I'm not sure if you're being facetious here. One can never tell on these boards. The fact is true. In fact, it's true with either the correct definition of "dark side" (where it's trivially true) or the erroneous confusion with "far side" (where it's true to distance to Sun and effect of eclipses).

13th November 2019, 02:49 PM	#820
sphenisc Philosopher Join Date: Jul 2004 Posts: 5,362	Originally Posted by RecoveringYuppy The fact is true. In fact, it's true with either the correct definition of "dark side" (where it's trivially true) or the erroneous confusion with "far side" (where it's true to distance to Sun and effect of eclipses). I think, using the correct definition, the light side of the moon gets more light than the dark side does.
sphenisc Philosopher Join Date: Jul 2004 Posts: 5,362	__________________ "The cure for everything is salt water - tears, sweat or the sea." Isak Dinesen

13th November 2019, 02:57 PM	#821
RecoveringYuppy Penultimate Amazing Join Date: Nov 2006 Posts: 10,346	Originally Posted by sphenisc I think, using the correct definition, the light side of the moon gets more light than the dark side does. Oh, duh, I should have re-read my original claim. You are of course correct. What I said only applies to the "so called dark side" as I originally stated.
	Last edited by RecoveringYuppy; 13th November 2019 at 02:59 PM.

13th November 2019, 03:04 PM	#822
JeanTate Illuminator Join Date: Nov 2014 Posts: 4,001	Originally Posted by Thor 2 As I am sure most here know, the Moon's spin matches its orbital rotation. This being why we always see the same side of the Moon from Earth - with a slight variation due to the elliptical orbit of the Moon. How many know why this is so? There are some other cool facts. Such as the 24-hour Earth affects the 28-day Moon via tides ... 24 is increasing (what is 28 doing?). So the cosmic coincidence that the Moon is ~the same size (on the sky) as the Sun is rather narrow (in geological time). Once the Moon was much closer (and tides were much bigger). And astronomical models of the Earth-Moon system match geological evidence going back almost to the earliest sedementary deposits. How can geologists estimate the number of days in a year, in a ~billion year old rock formation?
JeanTate Illuminator Join Date: Nov 2014 Posts: 4,001

13th November 2019, 04:29 PM	#823
Thor 2 Philosopher Join Date: May 2016 Location: Brisbane, Aust. Posts: 6,509	Originally Posted by arthwollipot I do. I'm not sure I could explain it technically, but there are several bodies in the solar system that are tidally locked with their parent. The term "tidal locking" has been used by some posters above but I haven't seen an explanation of how this works here. I read about it some time ago but can't find the explanation in an article again. I gained a fairly good grasp I think from my previous reading so here it is in my words: In the earlier days of the Moon's existence it was molten to a larger degree than today. The Moon would have had a faster speed of rotation than the current 28 days in the same direction as today (I think most orbiting bodies rotate in the same direction as the orbit) and as it rotated and being molten distorted due to Earths gravitational pull. We can refer to this molten flow as tidal. Distortion requires energy and that energy was taped from the rotational kinetic energy, causing the Moon's spin to slow down. Toward the end I imagine it would have maybe rocked back and forth, until its spin was in sync with the orbit.
	__________________ Thinking is a faith hazard.

13th November 2019, 05:13 PM	#824
ceptimus puzzler Join Date: May 2003 Posts: 6,460	I remember a long ongoing argument, maybe it was on this board, about whether the moon revolves with respect to the earth. One group argued that it did rotate, once per orbit, and the other group argued that with respect to the earth it didn't rotate - because if it did, we'd be able to see the other side. Both groups understood exactly what was happening, but they couldn't agree about how to correctly describe it, in English.
ceptimus puzzler Join Date: May 2003 Posts: 6,460

13th November 2019, 05:21 PM	#825
ceptimus puzzler Join Date: May 2003 Posts: 6,460	I remember someone used the analogy of a squirrel hiding, clinging on the opposite side of a tree trunk compared to where you're standing. As you walk around the tree, the squirrel moves too, so as to remain hidden, but it always faces towards you. After you've walked one complete circuit of the tree, the question then is, have you walked around the squirrel?
ceptimus puzzler Join Date: May 2003 Posts: 6,460

13th November 2019, 05:48 PM	#826
Delvo Дэлво Δελϝο דֶלְבֹֿ देल्वो Join Date: Jul 2008 Location: North Tonawanda, NY Posts: 9,206	It isn't quite completely locked. Its average orientation is locked, but it drifts minutely above and below, or ahead of and behind, that average. So the amount of its surface that can be seen from different parts Earth at different times is actually not half but almost three fifths. One part of the reason for that is actually a cheat, meaning by itself it doesn't mean the moon isn't tidally locked; it's just a matter of perception from Earth's surface making it look not quite so if one's observations are precise enough. It would still apply even if the "lock" were more all-encompassing and the following two phenomena after this paragraph didn't happen. It's that the moon can be simultaneously observed by different points on Earth at the same time that are up to roughly one Earth-diameter apart from each other. That sets up a stereoscopic effect by which you could see small differences if you compared simultaneously-shot images of it from far-flung points on Earth. It also means that you could observe a small amount of apparent rotation of the moon form a fixed point on Earth over the course of a single day/night as you moved from a moonrise point of view to a moonset point of view. Even if the following two things weren't real, this would still be the case. But also, there are two ways in which the moon is not perfectly locked. First, its axis of rotation is tilted, not perpendicular to the plane of its orbit. The geometric effect is exactly the same as with the angle of Earth's axis to Earth's plane or orbit, which causes the sun to "see" more of Earth's northern hemisphere during the northern summer and more of the southern hemisphere during the southern summer. We see more of the moon's northern hemisphere during one half of its orbit and more of its southern hemisphere during the other half. And second, while its speed of rotation and speed of movement along its orbital path match each other on average, the latter fluctuates more. In a non-circular orbit, the orbiting object moves slower (both in miles per time and in degrees per time as seen from the object it's orbiting) when it's farther away and faster (again both in miles per time and in degrees per time as seen from the object it's orbiting) when it's closer. Thus, the net effect of a constant rotation rate and an overall averaged-out 1:1 ratio of rotations to orbits combines to a small net forward (eastward) rotation near apogee and a small net backward (westward) rotation near perigee. Another way to look at the same thing is that if it's rotating once for each trip along an ellipse then the same face is always facing the point exactly halfway between the ellipse's two epicenters, which is not the same as always facing either epicenter, which is where the orbited object is; instead it means facing slightly back behind the nearest epicenter as it approaches one end of its orbit, and facing slightly ahead of the nearest epicenter as it moves away from that end of its orbit. An observer holding position in space between Earth and the moon, to always look straight at the moon and keep Earth at his/her back (thus eliminating any misleading or distracting effects that are caused by Earth's rotation & atmosphere alone) would see the moon doing this each "month" (moonth?): Image linked instead of embedded, to avoid having the host's server need to serve it whenever this page loads Notice the word "libration" in the link. That's the word to look up for more about this elsewhere.

13th November 2019, 06:09 PM	#827
arthwollipot Observer of Phenomena Pronouns: he/him Join Date: Feb 2005 Location: Ngunnawal Country Posts: 69,572	Originally Posted by ceptimus I remember a long ongoing argument, maybe it was on this board, about whether the moon revolves with respect to the earth. One group argued that it did rotate, once per orbit, and the other group argued that with respect to the earth it didn't rotate - because if it did, we'd be able to see the other side. Both groups understood exactly what was happening, but they couldn't agree about how to correctly describe it, in English. And that's clearly the only time that has ever happened.
	__________________ Please scream inside your heart.

13th November 2019, 06:12 PM	#828
sphenisc Philosopher Join Date: Jul 2004 Posts: 5,362	Originally Posted by ceptimus I remember someone used the analogy of a squirrel hiding, clinging on the opposite side of a tree trunk compared to where you're standing. As you walk around the tree, the squirrel moves too, so as to remain hidden, but it always faces towards you. After you've walked one complete circuit of the tree, the question then is, have you walked around the squirrel? https://www.imaginativeuniversal.com...-the-squirrel/
sphenisc Philosopher Join Date: Jul 2004 Posts: 5,362	__________________ "The cure for everything is salt water - tears, sweat or the sea." Isak Dinesen

14th November 2019, 02:05 AM	#829
Cheetah Master Poster Join Date: Feb 2010 Location: South Africa Posts: 2,690	What a ridiculously biased, self centered, conclusion that is. Totally and disgustingly speciest. Obviously it's the squirrel walking around the human, or not, depending on the squirrels definition of 'around'.
	__________________ "... when you dig my grave, could you make it shallow so that I can feel the rain" - DMB Last edited by Cheetah; 14th November 2019 at 02:12 AM.

14th November 2019, 07:13 AM	#830
Gord_in_Toronto Penultimate Amazing Join Date: Jul 2006 Posts: 20,141	Originally Posted by Cheetah What a ridiculously biased, self centered, conclusion that is. Totally and disgustingly speciest. Obviously it's the squirrel walking around the human, or not, depending on the squirrels definition of 'around'. Please let's not go there again. It will not end well. To quote the bowl of petunias: "Oh no, not again!" Originally Posted by Douglas Adams, The Hitchhiker's Guide to the Galaxy And wow! Hey! What’s this thing suddenly coming towards me very fast? Very very fast. So big and flat and round, it needs a big wide sounding name like … ow … ound … round … ground! That’s it! That’s a good name – ground! I wonder if it will be friends with me? And the rest, after a sudden wet thud, was silence. Curiously enough, the only thing that went through the mind of the bowl of petunias as it fell was Oh no, not again. Many people have speculated that if we knew exactly why the bowl of petunias had thought that we would know a lot more about the nature of the universe than we do now.”
	__________________ "Reality is what's left when you cease to believe." Philip K. Dick

14th November 2019, 11:10 AM	#831
Dr. Keith Not a doctor. Join Date: Jun 2009 Location: Texas Posts: 22,007	Originally Posted by sphenisc https://www.imaginativeuniversal.com...-the-squirrel/ The real joy of that is in the comments.
	__________________ Suffering is not a punishment not a fruit of sin, it is a gift of God. He allows us to share in His suffering and to make up for the sins of the world. -Mother Teresa If I had a pet panda I would name it Snowflake.

15th November 2019, 04:23 PM	#832
bruto Penultimate Amazing Join Date: Jun 2005 Location: Way way north of Diddy Wah Diddy Posts: 27,265	Originally Posted by GlennB I studied physics at school, but then there were quite a lot of them. Only one biology and chemistry though But a single bit of biology or chemistry would not put you out of action like a single dose of physic.
	__________________ I love this world, but not for its answers. (Mary Oliver) Quand il dit "cuic" le moineau croit tout dire. (When he's tweeted the sparrow thinks he's said it all. (Jules Renard)