The Earth, The Moon And, The Sun

It has become clear to me that our concept of the gravitational relationship between the earth, sun and, moon is far from accurate. Conventional wisdom is that the moon orbits the earth while the earth orbits the sun.

But how can the moon possibly orbit the earth? The sun is 400 times as far away from the moon as the earth is but the sun is about 331,950 times the mass of the earth. Since gravitational force is inversely proportional to the square of the distance and the square of 400 is 160,000, the sun exerts 2.07 times the gravitation force on the moon that the earth does.

A smaller body, such as the moon, will logically orbit the larger body that exerts the strongest gravitational force on it. This can only mean that the moon really orbits the sun and not the earth, regardless of how it appears to us. My conclusion is that both the earth and the moon follow the same fundamental orbit around the sun, which I will refer to as the mean orbital path. The moon appears to us to orbit the earth because it interweaves with the earth along the mean orbital path.

If the moon rotated freely, it would seem from there that the earth is orbiting the moon while the moon orbits the sun. Since the same side of the moon always faces the earth because of the earth's tidal force, this is not the case and the earth always remains in the same place in the lunar sky although the earth's phases change in the same way that the moon goes through phases as seen from earth.

Imagine an alternating weave of a thick line and a thin line around a straight line. The straight line represents the mean orbital path, the thick weaving line represents the earth and the thin weaving line represents the moon. The weave of the thin line, the moon follows exactly the same wavelength as the thick line, the earth, but it's weave goes much further from the baseline, the mean orbital path on each cycle.

The earth and moon both weave around the mean orbital path but the mass multiplied by distance from the mean orbital path remains the same. The moon weaves so much further away because it's mass is only 1/81 of the mass of the earth. The moon is 1/4 the earth's diameter and is made of the same type of rock as the earth's mantle but the earth has a heavy iron core that the moon is believed to lack.

The weave of the earth and the moon around the mean orbital path is due to their mutual gravity. It is a dance that has been going on for thousands of millions of years. imagine a donut-shaped (doughnut) concrete platform in space with a hole in the middle of it. Now suppose someone were to throw a ball upward from the platform. The ball would travel upward until the gravity of the platform pulled it back down. But, with no air resistance in space, the momentum of the fall back to the platform would propel the ball an equal distance on the opposite side of the platform as long as it went through the hole. Then it would come to a halt and fall back to the platform again and the cycle would continue indefinitely.

This is what happens in the dance of the earth and the moon as they travel along the mean orbital path around the sun. Both attract each other by gravity from opposite sides of the baseline but then go past the line in opposite directions due to momentum. But then each comes to a halt in their movement away from each other and the mean orbital path and then fall back toward each other again, all the while orbiting the sun.

The earth and moon cross the mean orbital path at the same time but not at the same point. Both earth and moon actually vary in their velocity in orbit around the sun, the moon a lot more than the earth due to it's relatively smaller mass. The moon moves around the sun due to the pull of the sun's gravity on it. But sometimes the moon is between the earth and the sun in it's interweaving with the earth. During this time the earth's gravity is on the opposite side to the sun in that it is pulling on the moon from the opposite direction as well, this causes the moon to speed up. At other times, the moon is on the other side of the earth from the sun so that the earth's and sun's gravity are both pulling on it from the same direction, this causes the moon to slow down. As we would expect, the moon moves faster when it is closest to the sun, demonstrating that the moon does actually orbit the sun.

The moon is on the mean orbital baseline, as is the earth, when we see the moon exactly half illuminated by the sun. It is moving more quickly so that it moves ahead of the earth when it's phase is less than half and it is moving more slowly so that it falls behind the earth in the orbit when it's phase is more than half illuminated, such as at full moon. Thus the moon alternates between pulling ahead of and falling behind the earth in the orbit around the sun, while maintaining roughly the same distance from earth. This causes the appearance of it orbiting the earth. We know that this scenario must be true, and not the reverse, because the moon orbits the earth going eastward.

If astronauts had lived on the moon for a period of time, they would have surely noticed this variation in speed every 29 earth days as it orbits the sun. The earth also moves faster when the moon is on the same side of it as the sun and vice versa but this variation has apparently been too slight for us to notice. However, this must be the way it is. The moon cannot possibly behave the same when the relative alignment of the earth and sun change. But since there is no visible change to us, the only possible change must be in velocity that causes us to perceive the moon orbiting the earth.

Once again, that is impossible if the sun exerts more than twice the gravitational force on the moon that the earth does. One full cycle in this dance is 46,394,937 miles (79,229,479 km) along the mean orbital path, or 29 days. So, the weaving of the earth and moon along this line would appear to an outside observer as very flattened versions of sine waves. This seems to have never been noticed before because it causes the earth's distance from the sun to vary by less than the earth's diameter and during the course of a year, the earth's distance from the sun varies by more than three million miles (4,800,000 km) anyway.

In "The Surface of The Moon", I described how the earth's tidal force on the moon caused the lava flows that produced the dark areas that we see on the moon and in doing so redistributed the moon's mass to reach a fine balance and stop the moon from rotating so that the same side of it always faces the earth. You may be wondering how the earth can have such a tidal effect on the moon while the sun apparently does not if the gravitational force of the sun on the moon is more than twice that of the earth.

Let me explain. This tidal effect is the result, not only of gravity but of a difference in gravity. If the force of gravity exerted on the earth's oceans by the sun and moon was exactly the same as the force they exerted on the rock layers under the ocean, there would be no tides. But the surface of the ocean is a few miles closer to the moon than the underlying earth.

This is what causes the tides, not the gravity but the difference in gravity. The tidal force is proportional to the gravitational force from the moon or sun divided by it's distance. The sun exerts 168 times the gravitational force on earth that the moon does but the sun is also 400 times as far away as the moon.

The result is that the tides in the earth's oceans by the moon are more than twice as high as those produced by the sun. This also means that on the moon, the tidal force produced by the earth is about 200 times that produced by the sun, even though the total gravitational force of the sun on the moon is more than twice that of the earth.

Imagine yourself on the moon. What would it be like? How would the sky look different than it does on earth?

It would depend which side of the moon you were on. The same side of the moon always faces earth, so that if you were on the far side of the moon you would never see the earth. From the far side of the moon, it would seem to be rotating to provide night and day, just as earth does. But, instead of 24 hours, a lunar day would last 29 earth days. Half would be dark, and half of that time would be light.

From the far side of the moon, the moon would not seem to rotate around it's center of mass, as the earth does, it would seem to be rotating around a point in space hundreds of thousands of kilometers away, which is where the earth is located. From the near side of the moon, the moon would seem to be rotating around it's center of mass.

It would not appear, from the moon, that the moon is revolving around the earth, as it appears to us from earth. It would appear that the moon is revolving around the sun, but with the moon's distance to the sun varying by nearly half a million miles, about 700,000 km, during the course of the month.

This variation in distance would not be apparent with the naked eye, but would be measured if there were astronomers on the moon. The variation in distance from the sun is caused by the gravitational influence of the nearby earth, but it would not appear that the moon is in orbit around the earth.

From the side of the moon facing earth, there would be the same lunar day equal to 29 earth days with half of the time being light and the other half dark. The difference, of course, would be the earth. The earth would not appear to move at all in the sky. No matter where an observer was, on the side of the moon facing earth, the earth would always be in the same place in the sky.

There is a photo taken from the moon by astronauts titled "earthrise", as opposed to sunrise. However, this cannot be technically correct because since the moon does not rotate, relative to the earth, the earth cannot "rise" or "set" in the lunar sky.

The location of the earth in the sky would be determined by the observer's latitude and longitude on the moon. An observer at the moon's north pole would see the earth at the southern horizon, and vice versa. The same for the eastern and western limits of the half of the lunar surface that is visible from earth.

The position of the earth in the lunar sky would be even more valuable for surface navigation than is the North Star (Polaris). A lunar traveler could readily tell both his latitude and longitude by taking a sighting on the position of the earth in the sky. As the traveler headed northward, the earth would appear further south, as the traveller moved westward, the earth would appear further east. Travelers on the far side of the moon would have no such advantage.

The earth would always be visible from the near side of the moon, whether it was day or night there. The earth would appear with about four times the angular diameter that the full moon appears to us on earth. The moon from earth occupies about half an angular degree, the earth from the moon would occupy about two angular degrees.

From the earth, the sun and moon appear as about the same size in the sky because, while the sun is about 400 times the diameter of the moon, it is also about 400 times as far away. But the earth would appear as four times the diameter in the lunar sky, and periodically lunar day would become night as the earth blocked out the sun in what we see as a lunar eclipse, but the moon would experience as we do a solar eclipse.

It would not be entirely dark, but would be reddish because the earth's atmosphere would refract some long-wavelength red light around and onto the moon. We can see this red shade on the moon during a lunar eclipse.

An observer on the near side of the moon would see the earth going through phases similar to the phases of the moon as seen from earth. The rotation of the earth would be easily visible, and thus an earth day could be used on the near side of the moon as a unit of time. The lights of cities could probably be seen as a faint and eerie glow on the earth's night side.

There is a rule that I have noticed concerning the phase relationship between the earth and moon. At any given time, the phase of the moon as seen from the earth, and the phase of the earth as seen from the moon, expressed as a proportion of the full disc, must add up to one full disc.

For example, when we see a full moon an observer on the moon would not see the earth illuminated by the sun at all. In other words, the lunar observer would see a "new" earth. When we cannot see the moon, because the moon is between the earth and the sun, we refer to it as the new moon. At that time, an observer on the near side of the moon would see a full earth. When we see a half moon, and observer on the moon would see a half earth.

An observer on the moon would definitely consider the moon as in orbit around the sun, and not the earth as we see it. The fact is that, from the moon, the gravitational influence of the sun is more than twice that of the earth. I find that just the fact that there are eclipses are proof of this. The plane of the moon's apparent orbit around the earth is tilted about 5 degrees relative to the plane of the earth's orbit around the sun. But yet periodically, the three end up in the same plane or else there would not be eclipses.

If the gravitational influence of the earth on the moon were greater than that of the sun, there would be no reason for the planes of the two to coincide. The earth would be able to hold the moon in an orbit, the plane of which would not at all need to be the same as that of the earth around the sun.

But due to the fact that it is the gravity of the sun which is stronger at the moon, the plane of the apparent path of the moon around the earth still diverges from that of the earth around the sun, but it must change so that while it may be above or below the orbit of the earth around the sun at any given time, it must average out to be the in the same plane as the orbit of the earth around the sun.

This is why there are eclipses, because periodically the plane of the two are the same. But if the plane of the two were always the same, there would be both a lunar and a solar eclipse every month.