The moon..... [Archive] - SciForums.com

superluminal

12-25-07, 07:17 PM

Yeah, I've asked that question. I still don't get it. I gave up trying cuz I was only embarrassing myself.
It's not that hard.

Try this link:

http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit4/tides.html

Enmos

12-25-07, 07:24 PM

The moon simply rotates at the same rate as it orbits. That's why we always see the same side of the moon.

http://enmos.eu/tempdir/moonrot.jpg

See that while the moon orbits around the earth that it spins exactly fast enough to keep the same side faced towards earth ?

superluminal

12-25-07, 07:25 PM

It's tidally locked.

Enmos

12-25-07, 07:26 PM

It's tidally locked.

Yep, I thought they just had difficulty to imagine how it spins while orbiting, to keep the same side faced towards earth.

superluminal

12-25-07, 07:29 PM

Yep, I thought they just had difficulty to imagine how it spins while orbiting, to keep the same side faced towards earth.
That's what I thought at first. It's suprising though how many people get the fact that it always keeps the same face toward the earth but don't realize that this means that it must be rotating - at exactly the same rate as its orbital period. Interesting.

Orleander

12-25-07, 07:30 PM

Yep, I thought they just had difficulty to imagine how it spins while orbiting, to keep the same side faced towards earth.

I don't understand. I cannot seem to put one brain cell in front of the other and take the step necessary to understand this. :wallbang:

Enmos

12-25-07, 07:31 PM

That's what I thought at first. It's suprising though how many people get the fact that it always keeps the same face toward the earth but don't realize that this means that it must be rotating - at exactly the same rate as its orbital period. Interesting.

That's what I meant lol ;)
I thought I'd fabricate a simplified picture to make them see..

Enmos

12-25-07, 07:32 PM

I don't understand. I cannot seem to put one brain cell in front of the other and take the step necessary to understand this. :wallbang:

Did you see the picture I posted ?

superluminal

12-25-07, 07:37 PM

I don't understand. I cannot seem to put one brain cell in front of the other and take the step necessary to understand this. :wallbang:

Here's what you need to do. Get two balls. Tennis balls, dog toys, whatever. Put them on a table. Pick one to be the earth. Hold it steady and make the other one (the moon) move around the earth in a circle. Wht do you have to do to the "moon" to make one side of it always face the "earth" as you circle it around the "earth"?

cosmictraveler

12-25-07, 09:36 PM

Did you know the moon is moving away from the Earth at about a foot or so a year? Eventually it will be so far away it won't influence the tides any longer. :eek:

Enmos

12-25-07, 09:39 PM

Did you know the moon is moving away from the Earth at about a foot or so a year? Eventually it will be so far away it won't influence the tides any longer. :eek:

Yea, we'll be in some shit then.. :D

cosmictraveler

12-25-07, 09:41 PM

Yea, we'll be in some shit then.. :D

It will be awhile, about 500,000 years or so from now.

superluminal

12-25-07, 09:43 PM

Did you know the moon is moving away from the Earth at about a foot or so a year? Eventually it will be so far away it won't influence the tides any longer. :eek:
Yep. But the actual current number is 3.8cm per year.

Source:
http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html

USS Exeter

12-25-07, 10:06 PM

It is a good thing the earth doesn't behave that way, one side would always be day and one side always night.

sly1

12-25-07, 10:09 PM

Yeah, I've asked that question. I still don't get it. I gave up trying cuz I was only embarrassing myself.

Kinda my same situation here......So in order to make myself understand I grabbed a couple bouncy balls and whala.....all the sudden i get it.

Still interesting though how the speed of rotation of the moon on its axis is sooooo similar to its orbit around the earth......"wow cool" I belive were my exact words.

sly1

12-25-07, 10:12 PM

Did you know the moon is moving away from the Earth at about a foot or so a year? Eventually it will be so far away it won't influence the tides any longer. :eek:

this would totaly be bogus to my shredding bra.....

superluminal

12-25-07, 10:12 PM

Here's what you need to do. Get two balls. Tennis balls, dog toys, whatever. Put them on a table. Pick one to be the earth. Hold it steady and make the other one (the moon) move around the earth in a circle. Wht do you have to do to the "moon" to make one side of it always face the "earth" as you circle it around the "earth"?

I truly am invisible.

USS Exeter

12-25-07, 10:14 PM

I truly am invisible.

I see you, hey guys, I found him! I found him! I found Superluminal!!! :D

superluminal

12-25-07, 10:15 PM

I see you, hey guys, I found him! I found him! I found Superluminal!!! :D
It's just that about four posts up I posted this way to show the tide locked rotation of... and then sly posts... oh, forget it.

Yorda

12-25-07, 10:30 PM

I don't understand. I cannot seem to put one brain cell in front of the other and take the step necessary to understand this. :wallbang:

both the earth and moon are magnets. the moon faces the earth because it's attracted by it, but they can never fall on each other because of magnetic repulsion. that's what i think at least.. and it's easy to understand.

Did you know the moon is moving away from the Earth at about a foot or so a year? Eventually it will be so far away it won't influence the tides any longer. :eek:

it's only temporary. later it will start moving towards the earth again. in a distant past, there was 360 days in one year, like in a circle.

when things are close to each other, there is greater attraction, and attraction makes things speed up, which causes distances to increase, that's why motions can't increase forever, because when distance increases, attraction decreases. and when motions slow down, attraction starts increasing again...

everything is so easy to explain... with magnetism...

Read-Only

12-25-07, 10:47 PM

everything is so easy to explain... with magnetism...

That's not quite it. You should have said, "Everything is so easy to explain when you don't have any idea what you are talking about." :D

sly1

12-25-07, 11:41 PM

It's just that about four posts up I posted this way to show the tide locked rotation of... and then sly posts... oh, forget it.

lol no worries....I actually did my little bouncy ball gig before I saw your reply to the post, I just didnt reply to the post right away when I was done.

Janus58

12-26-07, 12:56 AM

One thing to keep in mind is that the Moon doesn't keep exactly the same face towards the Earth at all times. The rotation of the Moon and its orbit don't keep in perfect step with each other. While their periods are the same, due to the eccentricity of the Moon's orbit, its orbital speed varies over its orbit. Thus the Moon's rotation at times gets ahead of and lags behind the orbit. As a result, the Moon shows a motion known as libration, where it "rocks" back and forth. Also, the Moons axis of rotation isn't perfectly perpendicular to the plane of its orbit, so there is a second libration, which cause the Poles to "nod" back and forth.

This all leads to something that looks like this if it where speeded up:
(The Moon also changes apparent size due to its orbital eccentricity.)
http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/moondance.gif

invert_nexus

12-26-07, 01:12 AM

Did you know the moon is moving away from the Earth at about a foot or so a year?

About 3.8 centimeters per year, actually. Just under 1.5 inches.

superluminal

12-26-07, 11:13 AM

Oh, right...

invert_nexus “ Did you know the moon is moving away from the Earth at about a foot or so a year? ”
About 3.8 centimeters per year, actually. Just under 1.5 inches.

About 10 posts ago:
Yep. But the actual current number is 3.8cm per year.

Source:
http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html

Sheesh.

cosmictraveler

12-26-07, 11:45 AM

About 3.8 centimeters per year, actually. Just under 1.5 inches.

My mistake. I forgot the exact number and took a stab at it. Thanks to both of you for that information. ;)

Cyperium

12-26-07, 01:18 PM

this would totaly be bogus to my shredding bra.....Yes, then the earth will not have a stable rotation anymore, as someone suggested, but will wobble. Luckely we still have the moon :)

Wouldn't be so fun not knowing when day or night will come...

If the moon didn't show the same face all the time, then the cultures in the past perhaps would have seen that it was round, and thus concluded that the earth was round too?

Perhaps it was meant to be, that's all.

Nikelodeon

12-26-07, 02:31 PM

This all leads to something that looks like this if it where speeded up:
(The Moon also changes apparent size due to its orbital eccentricity.)
http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/moondance.gif

Is this a stable wobbling or is it settling down?

orcot

12-26-07, 03:05 PM

Is this a stable wobbling or is it settling down?
setteling but only on a scale of billion years

Enmos

12-26-07, 03:26 PM

It will be awhile, about 500,000 years or so from now.

You are right, humankind will be long gone by then..

2inquisitive

12-26-07, 03:59 PM

setteling but only on a scale of billion years
How do you propose that the eccentric orbit (not a perfect circle) or the axis of rotation of the moon will change over time? Those two factors are responsible for the librations (wobbles) we see when the moon is viewed from the Earth, as Janus58 stated.

invert_nexus

12-26-07, 05:01 PM

About 10 posts ago:

Damn.
You are invisible.
I even gave a quick glance over the thread to see if someone had already mentioned this.

You must be a super hero.

superluminal

12-26-07, 05:06 PM

Damn.
You are invisible.
I even gave a quick glance over the thread to see if someone had already mentioned this.

You must be a super hero.
No, just superluminal. Apparently I post slightly faster than the speed of light so my posts end up travelling backward in time and just get missed. :shrug: