Science scratches its' head

[Nuclear]

Originally Posted by byHismercy

I'm not sure I understand this, but I have not studied astronomy in any depth at all. Maybe you can help me understand a question that niggles my brain these days....

Moon orbits the earth about once a day. Earth revolves on its' axis every 24 hours. Earth and moon together orbit the sun once every 364 1/4 days. And somehow, in a miraculous way, the moon appears to follow the sun's path in the sky, rising in the east and setting in the west every night. I just can't wrap my brain around this special relationship they have. I mean, HOW DOES THAT HAPPEN? Anybody elses' mind boggles witnessing Gods' creation?? If you can explain that.....

As far as I know, this isn't actually the case, which I think you did address in the followup. This would only seem to be the case from one day to the next, as the orbit of the moon is slow enough that relative to the sun it will seem to follow it at the same distance. However wait a week or two and it will be at a completely different spot, and only seems to follow it because both planes of orbit are the same.

Originally Posted by byHismercy

Edited to correct my mistake......according to Google, the moon orbits the earth every 27ish days, and simultaneously it revolves on its' own axis also once every 27 days, giving it the appearance of not revolving at all (we never see the far side of the moon from here).

And as far as this goes, its actually pretty cool how this works. If you take a look across the solar system, you'll find that with most moons on other planets this is also the case; that each moon only has one face to its planet at all times. This is because of a phenomenon known as Tidal Locking.

Essentially when a satellite at the scale of the moon orbits a planet as relatively close as the earth and moon, several interesting things happen. For one, the gravitational force difference between the far end of the moon and the far end is large enough to squeeze the moon into a sort of oval, its barely visible but its there. Imagine attaching a rope to the edge of a ball of play-do and swinging it around you, this is sort of how that would work. Its not a perfect analogy but it should get the point across.

What this change in shape does is change how the moon interacts with earths gravity. Imagine in this case attaching a rope to the "pointy end" of a football and swinging it around you. As you can imagine, no matter the position of the football when you start, it will always end up correcting itself and face a certain direction towards you. It may wobble and change orientation slightly (even the moon does this, depending on the time we may be able to see a bit of the rear face) but will always remain relatively stable. This has been observed in most cases of a moon orbiting a larger planet. Hope that helps!

[Ohio]

Originally Posted by Nuclear

And as far as this goes, its actually pretty cool how this works. If you take a look across the solar system, you'll find that with most moons on other planets this is also the case; that each moon only has one face to its planet at all times. This is because of a phenomenon known as Tidal Locking.

Essentially when a satellite at the scale of the moon orbits a planet as relatively close as the earth and moon, several interesting things happen. For one, the gravitational force difference between the far end of the moon and the far end is large enough to squeeze the moon into a sort of oval, its barely visible but its there. Imagine attaching a rope to the edge of a ball of play-do and swinging it around you, this is sort of how that would work. Its not a perfect analogy but it should get the point across.

What this change in shape does is change how the moon interacts with earths gravity. Imagine in this case attaching a rope to the "pointy end" of a football and swinging it around you. As you can imagine, no matter the position of the football when you start, it will always end up correcting itself and face a certain direction towards you. It may wobble and change orientation slightly (even the moon does this, depending on the time we may be able to see a bit of the rear face) but will always remain relatively stable. This has been observed in most cases of a moon orbiting a larger planet. Hope that helps!

The earth is a satellite around the sun, and it's not a perfect sphere either.

So ... I'm thinking the earth should have a hemisphere facing the sun -- global warming -- and a hemisphere facing away from the sun -- ice age.

Tidal Locking in action!

[Nuclear]

Originally Posted by Ohio

The earth is a satellite around the sun, and it's not a perfect sphere either.

So ... I'm thinking the earth should have a hemisphere facing the sun -- global warming -- and a hemisphere facing away from the sun -- ice age.

Tidal Locking in action!

Your actually right on this one! Both the moon and the sun both exert Tidal Locking on the earth, but as you can imagine, the moon is not nearly at doing it to the extent as we are to the moon. The sun also exerts a similar force but because of the massive distance between us and the sun, the difference between the far edge of our planet and the close edge is not significant to have a noticeable affect, but it is measurable. Its essential to understand that these sorts of forces happen over astronomical periods of time. For this very reason earths day becomes longer by 15 microseconds every year, but at this rate the Sun becomes a red giant and engulfs the planet before we ever reach that sort of synchronous orbit.

[Ohio]

Originally Posted by Nuclear

Your actually right on this one! Both the moon and the sun both exert Tidal Locking on the earth, but as you can imagine, the moon is not nearly at doing it to the extent as we are to the moon. The sun also exerts a similar force but because of the massive distance between us and the sun, the difference between the far edge of our planet and the close edge is not significant to have a noticeable affect, but it is measurable. Its essential to understand that these sorts of forces happen over astronomical periods of time. For this very reason earths day becomes longer by 15 microseconds every year, but at this rate the Sun becomes a red giant and engulfs the planet before we ever reach that sort of synchronous orbit.

Perhaps God intervened to get the earth spinning correctly in Gen 1.3-5?

[Nuclear]

Originally Posted by Ohio

Perhaps God intervened to get the earth spinning correctly in Gen 1.3-5?

Its certainly possible and there are theories that earths rotational speed has been changed due to impacts with other solar and interstellar bodies, how you choose to interpret these events is up to you I suppose.

As far as what has been currently determined is that the earth's day was 5 hours long during early formation, whether this is from angular momentum or other events is still up for debate, but tidal locking has slowed it to the approximately 24 hours that it is now.