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Seeka
2009-Feb-03, 06:20 PM
Not a very challenging or exciting thread but can someone please explain to me how we only see one side of the moon?
I know it is gravitationally locked but what does this mean?
Also, how can it rotate and still show us just one side, if it is rotating then we should see all sides surely?:confused:

I had it explained to me last evening at a viewing session at my local observatory, but having a few other people also listening i was too embarrassed to say, huh? Which is what i was thinking!

Much appreciated,

Steff.

speedfreek
2009-Feb-03, 06:47 PM
The moon takes around 28 days to orbit the Earth, during which time it rotates once. If you imagine the system from above you will see that if it only rotates once during its orbit, it will always have the same face pointing at the Earth.

You might imagine it using the hands of a clock. If you stick a coin on the tip of the minute hand, as the hand moves around the clock the same part of the coin is always pointing towards the centre of the clock-face. After the minute hand has been around the clock once, the coin will have rotated once.

NEOWatcher
2009-Feb-03, 06:54 PM
Here's some more simple thoughts:

I know it is gravitationally locked but what does this mean?
One side is heavier than the other. The heavier side will tend to point toward the most gravity which would be the earth.

Similar to how an out of balance suspended bicycle wheel will settle to the heavy side down. Now if you move that wheel around the Earth, it wall always point that way, thus making one full circle (from a non-Earth point of view).


Also, how can it rotate and still show us just one side, if it is rotating then we should see all sides surely?:confused:
Tie a bucket of water to a rope and spin it around. It's rotating, yet you are only seeing one side of it because you are in the center.

Fiery Phoenix
2009-Feb-03, 07:05 PM
To put it simply, the Moon's rotation period just happens to be equal to its orbital period around the Earth. This is why we only see one side of the Moon.

hhEb09'1
2009-Feb-03, 07:14 PM
One side is heavier than the other. The heavier side will tend to point toward the most gravity which would be the earth.In the case of the moon (http://www.bautforum.com/space-astronomy-questions-answers/84111-tidal-locking-need-understand.html#post1422195), the "heavy side" of the moon is not pointed directly towards the Earth. It's a few tens of degrees off, if I recall correctly

the Moon's rotation period just happens to be equal to its orbital period around the Earth. It's not just a coincidence though, a lot of moons are locked to their larger planets. The induced tides can slow down a satellite.

pzkpfw
2009-Feb-03, 07:30 PM
I like pictures:



Moon orbiting Earth, tidally locked so showing one face to Earth:


1 2 3 4

m
v
m> E E E <m E
^
m


Seen from Moon point of view:

E
^
m> E m E <m m
v
E


Moon is rotating:

^
m> m <m m
v

NEOWatcher
2009-Feb-03, 07:31 PM
In the case of the moon (http://www.bautforum.com/space-astronomy-questions-answers/84111-tidal-locking-need-understand.html#post1422195), the "heavy side" of the moon is not pointed directly towards the Earth. It's a few tens of degrees off, if I recall correctly.
Actually, I never heard that. Darn media and public schools have always said that to me.
So; the tidal forces were more of a predomonent factor? Although, won't the moon eventually settle with the "heavy side down" (millions of years or more).

Seeka
2009-Feb-03, 10:36 PM
:wall::eh: I am so frustrated right now because i cannot seem to grasp this idea. I'm a smart person but i'm still lost! I appreciate you guys for replying.

I can sort of see what you guys are saying, still have difficulty with the same side facing us. Unless it turns with us as we turn an dthat just dosen't make sense to me.

Nick Theodorakis
2009-Feb-03, 10:44 PM
:wall::eh: I am so frustrated right now because i cannot seem to grasp this idea. I'm a smart person but i'm still lost! I appreciate you guys for replying.

I can sort of see what you guys are saying, still have difficulty with the same side facing us. Unless it turns with us as we turn an dthat just dosen't make sense to me.

It rotates with the exact same period as its orbit.

Try this: Put a lamp on the floor in the middle of the room, and stand facing it. Now shuffle along in a circle around the lamp, but keep facing it as you are going around it. That is what the moon is doing. You will have rotated once at the same time you went around the lamp once.

Nick

hhEb09'1
2009-Feb-03, 10:51 PM
Try speedfreek's idea. Seriously. You don't have to have a clock if you don't have one, just use a coin in one hand and move it around your other hand. Let the heads side of the coin face your other hand--notice that as you move it around the back side (tails) faces opposite parts of the room--it's rotating. Or, try Nick's idea.

Short answer: Try it!

cosmocrazy
2009-Feb-03, 10:58 PM
Here is a simple diagram.:)

Hornblower
2009-Feb-03, 11:05 PM
Here's some more simple thoughts:

One side is heavier than the other. The heavier side will tend to point toward the most gravity which would be the earth.
Not necessarily. In free fall it will be stable with either the heavy or the light side toward the Earth. Whichever is lower will accelerate faster, thus tending to align the long axis of the mass distribution with the gravity vector. That is different from the case of an unbalanced wheel on a stationary bearing. In that case the bearing places a nongravitational constraint on the motion, a constraint that is not present with a satellite in free fall.

Clear as mud? I realize this can be hard to visualize from words alone.

Hornblower
2009-Feb-03, 11:10 PM
In the case of the moon (http://www.bautforum.com/space-astronomy-questions-answers/84111-tidal-locking-need-understand.html#post1422195), the "heavy side" of the moon is not pointed directly towards the Earth. It's a few tens of degrees off, if I recall correctly

It appears that this reputed feature referred to as the "heavy side" does not accurately depict the actual mass distribution.

Can you identify a source for that remark?

hhEb09'1
2009-Feb-03, 11:12 PM
It appears that this reputed feature referred to as the "heavy side" does not accurately depict the actual mass distribution.

Can you identify a source for that remark?Looked for one a couple hours ago. :)

How about yours?

ETA: From Nine Planets (http://www.nineplanets.org/luna.html)
Curiously, the Moon's center of mass is offset from its geometric center by about 2 km in the direction toward the Earth. Also, the crust is thinner on the near side. Which is what I've always heard, but that also it's not directly towards the Earth. I'll see if I can dig up something else.

Seeka
2009-Feb-03, 11:23 PM
It rotates with the exact same period as its orbit.

Try this: Put a lamp on the floor in the middle of the room, and stand facing it. Now shuffle along in a circle around the lamp, but keep facing it as you are going around it. That is what the moon is doing. You will have rotated once at the same time you went around the lamp once.

Nick

Am i confusing rotation with orbiting? If i (the moon) will have rotated once by the same time i went around the lamp (which is earth), how is there not a time when my back is facing the lamp?!

Myself and my bf are killing each other trying to simulate the moons rotation in our living room:lol:

Peter B
2009-Feb-04, 12:45 AM
Nick Theodorakis said:
Try this: Put a lamp on the floor in the middle of the room, and stand facing it. Now shuffle along in a circle around the lamp, but keep facing it as you are going around it. That is what the moon is doing. You will have rotated once at the same time you went around the lamp once.

Steffanie said:
Nick

Am i confusing rotation with orbiting? If i (the moon) will have rotated once by the same time i went around the lamp (which is earth), how is there not a time when my back is facing the lamp?!

Myself and my bf are killing each other trying to simulate the moons rotation in our living room

Read again the bit in bold in Nick's quote. Keep facing the lamp as you shuffle around it. What you're doing is facing the same wall as you shuffle around the lamp.

There is a difference between the two actions.

Just to clarify, you complete a rotation on your axis once you've faced all four walls in the room. That will happen to take as long as it takes for you to complete one orbit of the lamp.

Tobin Dax
2009-Feb-04, 01:26 AM
Am i confusing rotation with orbiting? If i (the moon) will have rotated once by the same time i went around the lamp (which is earth), how is there not a time when my back is facing the lamp?!

Myself and my bf are killing each other trying to simulate the moons rotation in our living room:lol:

Stand against a wall and watch your boyfriend as he moves around the lamp. He'll always be facing the lamp, but you'll see all sides of him as he goes around. He's spun around once from your point of view, so you've seen him go through one full rotation. He's also gone through one full orbit around the lamp, and it took the same amount of time.

Edit: Read what Peter B. said. Make your boyfriend face toward the lamp the whole time he's moving around it.

Hornblower
2009-Feb-04, 03:29 AM
Looked for one a couple hours ago. :)

How about yours?

ETA: From Nine Planets (http://www.nineplanets.org/luna.html) Which is what I've always heard, but that also it's not directly towards the Earth. I'll see if I can dig up something else.
I can imagine the possibility that irregular, lumpy concentrations of heavy material deep inside the Moon could displace the center of mass diagonally from the geometric center, rather than merely 2km along the geometric long axis of the surface. That could cause the best-fit prolate ellipsoid to be misaligned from the Earth.

Just imagine the possibility that exaggeration of the asphericity gives us something more like a potato than an egg.

NEOWatcher
2009-Feb-04, 12:43 PM
Clear as mud? I realize this can be hard to visualize from words alone.
I think I'm half way there knowing that the center of gravity is no longer the center of rotation for the wheel.

Tog
2009-Feb-04, 01:46 PM
:wall::eh: I am so frustrated right now because i cannot seem to grasp this idea. I'm a smart person but i'm still lost! I appreciate you guys for replying.

I can sort of see what you guys are saying, still have difficulty with the same side facing us. Unless it turns with us as we turn an dthat just dosen't make sense to me.

Try this. You'll need a room and a friend, or object that can serve as one.

The friend, or friend-like (FLO) object is placed in the middle of the room. You will represent the Moon. To that end, you face the FLO. On the other side of the FLO you will see a wall. This wall is now "Wall 1".

Now take one step to your right and turn as needed to keep facing your friend. Each time you take a step, adjust slightly to keep your facing consistent. Soon, you will be 25% of the way around the room.

If you don't rotate to face the FLO you will crash into a wall.

At the 1/4 mark, You should be facing a new wall. "Wall 2". Wall 1 will be to your right. Keep doing this until you end back in the original position, or near it.

Along your trip around the room, you should have had the FLO centered in your view, while the background walls kept changing. By the end of your trip, you will have seen the FLO in the foreground of every wall in the room. But the FLO will have only seen your face. Never the back of your head.

Now, step into the same place as the FLO, or as close as you can get. Spin one time, slowly, to your left, and you will see the walls pass around you in the same way they did when you "orbited" your friend.

When dealing with the real moon, the background stars are the walls, and the Earth is the Friend. During a full moon, the sun will be behind the Earth as seen from the moon. The view will be the same as on the Earth at mid-day.

During a new moon, the view will be the same from the moon, as it is from the Earth at mid-night. These two times take about two weeks to pass, so there will be a slight change because of the orbit, but from the moon, the sun will rise, move across the sky, and set, just as it does on Earth, It will just take days instead of hours to do it.

Does that help?

hhEb09'1
2009-Feb-04, 02:46 PM
I can imagine the possibility that irregular, lumpy concentrations of heavy material deep inside the Moon could displace the center of mass diagonally from the geometric center, rather than merely 2km along the geometric long axis of the surface. That could cause the best-fit prolate ellipsoid to be misaligned from the Earth.There are two different shapes involved here--one is the actual surface shape, the other is the mass distribution, which is reflected in the shape of the gravity field. On the Earth, the gravity field equipotential surface (the geoid) has a relief of a few hundred meters after the twenty kilometer equatorial bulge is accounted for, whereas the surface obviously has a much greater relief (Mt. Everest is almost nine thousand meters above sea level).

The moon shape (http://www.ipgp.jussieu.fr/~wieczor/SH/SH.html) is can be represented by spherical harmonics ("Degree 359 shape model of the Moon derived from the USGS Unified Lunar Control Network 2005 "), the coefficients of which are:

0 0 1737025.82132502 0.000000000000000
1 0 147.488719624524 0.000000000000000
1 1 -985.035952958352 -422.005429835170
2 0 -705.984306653320 0.000000000000000
2 1 -778.071552512909 -0.397858856690212
2 2 85.3781176271541 395.764151767781
3 0 63.7994229702025 0.000000000000000
3 1 568.005959384810 87.1612559253587
3 2 469.590091713719 153.342161993025
3 3 423.630343614396 -16.3014823621007

The degree n (n,0) coefficient is always zero (actually it doesn't exist), except for n=0. The (0,0) coefficient is the average radius, which the table reports as 1737 kilometers (about a half kilometer different from what appears at Planet Scapes (http://solarviews.com/eng/moon.htm)). The (1,n) coefficients represent a shift of the center of mass from the geometric center, and can be resolved into a single shift along an axis. The (2,0) coeffiicient represents the equatorial bulge, and the (2,2) coefficients the "pinching" of the equator. The (2,1) coefficients represent how much the degree two shapes deviate from axial symmetry. The (3,0) coefficient is the so-called "pear-shape" coefficient.

I'll see if I can dig up the lunar gravity field data.

ETA: The same website (http://www.ipgp.jussieu.fr/~wieczor/CrustalThicknessArchive/CrustalThickness.html) has some coefficients (Spherical harmonic coefficients of the lunar potential field LP150Q (Konopliv et al., 2001))

4902.80107600000
2 0 -9.090109494810000E-005 0.000000000000000
2 1 -1.862736081840000E-009 -1.424538946100000E-009
2 2 3.463762742080000E-005 1.440635035400000E-008
3 0 -3.203071679590000E-006 0.000000000000000
3 1 2.634183586220000E-005 5.463078608820000E-006
3 2 1.418533167860000E-005 4.889139117950000E-006
3 3 1.228626450440000E-005 -1.782462707200000E-006
Hmm, these seem to be in a bit different scale. There are no (1,x) coefficients (they're identically zero), because when the center of mass is the center of coordinates, there is no shift.

ETA: This article from 1969 (Science, Kaula) (http://www.sciencemag.org/cgi/reprint/166/3913/1581.pdf?ijkey=1cd315bf1cb7719aed5b2df48f7f7401b8e 1c280) is online, and it shows that the 4902 figure is GM, the product of the gravitational constant and the mass of the moon. The other figures are fairly close to the Michael et al. figures in its Table 2 (the (2,1) coefficients are smaller in the above--the size of the (2,1) coefficients result in what is known in the Earth as the Chandler wobble).

hhEb09'1
2009-Feb-04, 02:50 PM
Myself and my bf are killing each other trying to simulate the moons rotation in our living room:lol:You are definitely doing it wrong! :)

Instead of killing each other, hold hands, both hands, facing each other, arms extended so that you're pulling each other. Now, have the bf turn around while you go around him in a circle. You will face him continually. But notice that sometimes during the circle you can look out a window, other times you have your back to the window--that means you are rotating.

NEOWatcher
2009-Feb-04, 03:00 PM
...Instead of killing each other, hold hands, both hands, facing each other, arms extended so that you're pulling each other...
That one seems to be in every "chick flick". Except the camera is usually in a retrograde orbit.

Kelfazin
2009-Feb-04, 06:34 PM
Try this. You'll need a room and a friend, or object that can serve as one.

<snip>

Does that help?

Nicely described :)

Argos
2009-Feb-04, 07:43 PM
This visualization (http://www.astro.washington.edu/users/larson/Astro150b/Lectures/EarthMoon/earthandmoon.html#rotmoon) might help.

Tim Thompson
2009-Feb-04, 07:48 PM
I am so frustrated right now because I cannot seem to grasp this idea.
Sometimes there is no substitute for face to face interactions with other people. It's easiest to understand the moon rotation thing if somebody demonstrates it to you. The header says you are in Cork, Ireland. So I suggest you contact the Cork Astronomy Club (http://www.corkastronomyclub.com/). This is one of the things that amateur astronomy groups are really good at. You can learn a lot about this, and all manner of topics in astronomy, through personal involvement in an astronomy club or society. So I suggest you take this problem to them and they can show you how it works.

And don't think you should be embarrased about "not getting it". In fact most people "don't get it", and your question is a common question. I took part in a workshop some years ago where we as astronomers taught elementary school teachers about the rotation and phases of the moon. It was not an easy task; we were teaching teachers, not students, and at the end of the day we still had a couple of teachers who still had problems with it. So in fact it really is harder for non astronomers to understand the rotation of the moon than it is for those of us who are more involved in astronomy.

Kelfazin
2009-Feb-04, 08:05 PM
Also, to build a little onto what Tim said, almost every astronomer I've met LOVES to answer questions and describe how the sky works. These kinds of questions never get old. That's one of the main reasons this message board even exists. Astronomers love to talk about astronomical stuff :)

speedfreek
2009-Feb-04, 08:21 PM
I think the problem is due to relativity! You have to adopt a different point of view in order to appreciate that the Moon is rotating as it orbits the Earth. From the point of view of someone on Earth, the Moon always presents the same side to them.

Imagine you are standing on the moon as it orbits the Earth. You are standing on the side of the Moon that always faces the Earth. As you watch the Earth over a long period of time you will see that the Earth is rotating. In the time it takes the Moon to do one complete orbit, the Earth will have rotated 28 times.

Now move your viewpoint out into space so you can see both the Earth and the Moon. Over that same 28 days you will see the Earth rotate 28 times whilst the Moon makes one orbit. If you watch the Moon as it makes that orbit, you will see that the same side of the Moon always faces the Earth - the Moon will be slowly rotating as it orbits, so as to keep the same side facing the Earth.

If we call the side of the Moon that is visible from Earth the "near side" and the other side the "far side", and move our viewpoint way out past the Moon and then look back, we will be seeing all of the "far side" of the Moon with the Earth behind it. 7 days later the Moon will have made a quarter of an orbit and will be to the left of the Earth and we can now see half the "near side" and half the "far side" of the Moon. Another 7 days and the Moon will have moved round behind the Earth as it has made half of its orbit, so now the "near side" of the Moon is completely facing us (but we cannot see it if the Earth is in the way, of course. If our viewpoint were a little higher we could look over the top of the Earth and see the "near" side of the Moon facing us in the distance). 7 days more and the Moon is now three quarters of the way through its orbit, it is now to the right of the Earth and we can see the other half of the "near" and "far" sides. Once the Moon completes its orbit we can see only the "far" side once more.

From this external viewpoint, all sides of the Moon have been facing towards us during the orbit, so the Moon has rotated once.

Seeka
2009-Feb-04, 09:17 PM
Oh dear god i have seen the light! How could i have been so silly! I admit guys it was the link Argos suggested that clinched it for me. I knew i would have to see something visual, thanks Argos:) Also to everyone else you have the patience of a saint.

In response to Tim Thompson i am a new member to the Cork Astronomy club since December:)

cosmocrazy
2009-Feb-04, 09:19 PM
Oh dear god i have seen the light! How could i have been so silly! I admit guys it was the link Argos suggested that clinched it for me. I knew i would have to see something visual, thanks Argos:) Also to everyone else you have the patience of a saint.

In response to Tim Thompson i am a new member to the Cork Astronomy club since December:)

Well done! i had similar trouble getting it when i first tried to understand how it works! ;)

Seeka
2009-Feb-04, 09:34 PM
That was the most baffling idea i have tried to understand ever!

Kelfazin
2009-Feb-04, 09:40 PM
That was the most baffling idea i have tried to understand ever!

I spent about two weeks trying to explain this to my girlfriend and it entailed a whole lot of me walking in circles around the coffee table. It finally clicked for her in the same way...very much a "OOOhhhh now I see it!" way.

Now she explains it to other people lol.

Seeka
2009-Feb-04, 10:06 PM
I can imagine Kelfazin!
I had someone on the phone today trying to get me to stand in the car park at work and try orbitting a lamp post:lol: I reckon i would have been fired if my boss saw me. :D

Centaur
2009-Feb-04, 10:26 PM
...can someone please explain to me how we only see one side of the moon?
I know it is gravitationally locked but what does this mean?
Also, how can it rotate and still show us just one side, if it is rotating then we should see all sides surely


Steff, he Moon revolves around the Earth every 27.32 days. It also rotates on its axis during the same 27.32 days. This is no mere coincidence. It is due to tidal locking induced by asymmetrical mass distribution within the Moon. The natural satellites of other planets rotate in a similar manner.

If you were to stand on a merry-go-round always facing its center, both you and the device would turn at the same rate, yet the operator near the central pole would only see your front side.

BTW, the 27.32 days I mentioned is not to be confused with the Moon’s 29.53-day synodic cycle of phases. The latter is based on the Moon’s relation to the Earth and Sun. The Sun appears to shift through the zodiac as the Earth orbits it, so the Moon needs a couple of extra days to catch up to it.

Swift
2009-Feb-04, 10:28 PM
Oh dear god i have seen the light! How could i have been so silly!
\Henry Higgins mode\

I think she's got it!

cosmocrazy
2009-Feb-04, 10:42 PM
I can imagine Kelfazin!
I had someone on the phone today trying to get me to stand in the car park at work and try orbiting a lamp post:lol: I reckon i would have been fired if my boss saw me. :D


Are you sure it wasn't an excuse to get you to do some pole dancing.:dance:.:eek:

:think:hmmmm... i wonder..:D:D

Seeka
2009-Feb-04, 11:03 PM
:o:think: I never thought of that Cosmocrazy:D Perhaps they were. Tut Tut.

So, while on the topic, do we know what the far side of the moon looks like?
Also, if the moon was not tidally locked and it took longer to orbit would we see all sides? (or have i undone all the educating i've had by asking this question)

Kelfazin
2009-Feb-04, 11:28 PM
:o:think: I never thought of that Cosmocrazy:D Perhaps they were. Tut Tut.

So, while on the topic, do we know what the far side of the moon looks like?

We do, you could do a google image search for those. We've had a number of satellites (as well as the men of the Apollo missions) in orbit around the moon taking tons of pictures.

Hornblower
2009-Feb-04, 11:55 PM
This discussion demonstrates the fact that a picture, especially a moving one, can be worth more than a thousand words. It is not uncommon for highly intelligent, educated people to have difficulty in forming a proper mental picture of compound motion from words alone.

A friend of mine had trouble grasping the analogous case of the Big Dipper keeping its pointers aimed at Polaris as it moved around in a circle in the sky. When I got out my circumpolar star chart and demonstrated the motions by rotating the chart, it became perfectly clear to him.

Kelfazin
2009-Feb-05, 12:02 AM
That brings an interesting question: when you guys visualize the moving sky, do you visualize yourself as motionless as the sky rotates overhead, or do you visualize the sky motionless as we revolve on our axis?

For me it's the latter, it helps me maintain a much better 3D map of the sky in my head.

Brilliant Aberration
2009-Feb-05, 03:17 AM
That one seems to be in every "chick flick". Except the camera is usually in a retrograde orbit.

i nominate this for post of the day.

funny how this thread had two conversations going--one was explaining the distinction of revolution/rotation to a newcomer, and the other was invoking spherical harmonics to explain why the moon is tidally locked with THIS face as opposed to THAT face.

i love this place.

Seeka
2009-Feb-05, 10:40 AM
That brings an interesting question: when you guys visualize the moving sky, do you visualize yourself as motionless as the sky rotates overhead, or do you visualize the sky motionless as we revolve on our axis?

For me it's the latter, it helps me maintain a much better 3D map of the sky in my head.

I am the opposite to you Kelfazin, i couldn't imagine seeing things the way you do! Funny how people are different. Even with people giving me excellent easy descriptions i could kind of see what you were getting at but it wasn't until i saw Argos' link with the revolving porsche until i truely understood.
The Porshe was a poor choice though, should have used an Ferrari 599:D

I'm a dedicated trainer at work and when we have new staff that need to be trained i always suss out what kind of learners they are, if they prefer demonstrations or getting stuck in with my guidance, some people get it from just a simple description. It is interesting.
I will do a search on the moons far side images.

Argos
2009-Feb-05, 11:53 AM
Steffanie, thank you. Seeing that spark of understanding on people´s face is one of the most rewarding things in life. ;)

Jeff Root
2009-Feb-05, 01:11 PM
I think it was on the summer solstice in 2005 that I attended a public
program of the Minnesota Astronomical Society in the afternoon before
the star party. The people who were going to give a talk were setting
up the projector, which of course had a technical problem requiring a
connector from offsite, creating a delay. When people outside the
observatory door saw the light on the projection screen they started
coming in and sitting down. Nobody else seemed to notice them, so I
decided to just start talking about astronomy. The easiest thing to do
was take questions. One of the questions was exactly the question of
this thread, about the Moon's rotation. I started to try to demonstrate
with my hands, and the guy from the Minnesota Planetarium Society,
Parke Kunkle, came to my rescue and orbited around me as the Moon
while I rotated as the Earth.

-- Jeff, in Minneapolis

hhEb09'1
2009-Feb-05, 01:29 PM
funny how this thread had two conversations going--one was explaining the distinction of revolution/rotation to a newcomer, and the other was invoking spherical harmonics to explain why the moon is tidally locked with THIS face as opposed to THAT face.Usually, in the Questions and Answers forum, we try not to let the topics stray too far from the Original Poster's question, but in this case steffanie asked two questions and the answers diverged somewhat in technical level. The discussion might engender another question, posted to another thread.

i love this place.Welcome to BAUT! :)

Kelfazin
2009-Feb-05, 04:50 PM
I am the opposite to you Kelfazin, i couldn't imagine seeing things the way you do! Funny how people are different.

I think for me it's because, for all intents and purposes, the stars we see are static, they don't move relative to each other in a way that we can perceive in our individual life spans. So since I know those are static, I must be the one moving relative to them. I guess you can think of it like driving in a car. When I'm driving, the car isn't moving relative to me, but it is moving relative to the buildings. So just as we don't think of the buildings flying past while we sit still, I don't think of the stars flying by while the Earth sits still.

Using that model, when I visualize the sky in my head, I "zoom out" and view the Earth as a whole, with the stars surrounding it. That way, when I'm trying to figure out why Orion hasn't risen yet, I look at my internal map, realize it's on the other side of the Earth from me, and look for something else to point the telescope at :)

Peter B
2009-Feb-06, 03:53 AM
Also, if the moon was not tidally locked and it took longer to orbit would we see all sides? (or have i undone all the educating i've had by asking this question)

Yes we would, and no you haven't. ;-)

Jens
2009-Feb-06, 04:31 AM
That brings an interesting question: when you guys visualize the moving sky, do you visualize yourself as motionless as the sky rotates overhead, or do you visualize the sky motionless as we revolve on our axis?


I tend to do the opposite, just because it is hard to imagine it any other way. Even when I'm in a train, I tend to feel that the scenery is moving. Actually, although you say the opposite, the use of the term "moving sky" at the beginning makes it seem like the sky is the one that's moving. :)

Tog
2009-Feb-06, 07:06 AM
That brings an interesting question: when you guys visualize the moving sky, do you visualize yourself as motionless as the sky rotates overhead, or do you visualize the sky motionless as we revolve on our axis?

I think I tend to look at it both ways. I understand how the Earth, Sky and Moon, all work in relation to each other, so when I see a star "rise", I know it's because we rotated far enough over to see it, but I'll also think of it as having come "up".