# Uncovering the Truth About the Moon's Orbit and the Universe's Expansion

• SF
In summary, the moon orbits the Earth but its motion around the sun is the dominant factor. The expansion of the universe has a negligible effect on the distances in the solar system.
SF
Found this in another forum:

1) Is the moon really orbiting the earth?

The sun already has greater gravitational effect (stronger force) on the moon than the Earth does. (If you do not believe, calculated the relative Mass/separations^2 ratios for both sun and Earth (except for factor "G", the gravitational force at the moon).

In fact, the moon is now going arround the sun in essentially the same elliptic orbit as the Earth is. I.e. The moon only appears to be going around the Earth when viewed from the Earth. In fact, it is always with a trajectory that is curving towards the sun. Never is the moon on a trajectory that is convex towards the sun (as you would expect it to be if it were going around the Earth like most man made satellites are).

If the Earth were magically removed there would be very little difference in the moon's orbit about the sun. That orbit now has slight
"wobbles" about the true ellipse, which are caused by the relatively weak gravity from Earth and of course if Earth disappeared or had no gravity, they would cease to exist, but viewed from Mars, it would not be a noticable change in the moons orbit if the Earth had zero gravity. Earth does NOT control the moon. Really Earth does not have a natural moon, but is the larger of two interacting masses that co-orbit the sun.

Thread is badly named, reflecting this common erroneous POV. Should be called "Sun's planatoid near Earth" or something like that.

2) What is the effect of the Universe's expansion on the Moon/Earth or Sun/Earth distance?
http://www.news.cornell.edu/stories/March06/CMB_Timeline300.jpg
From that image, there's been about 10-20% universe expansion during the last 4 billion years.
Does that translate into any effect on the "small" distances in our Solar System?

Thanks.

Last edited by a moderator:
1) Yes the moon is orbiting the Earth, but very slowly (it only goes around the Earth about 12 times a year), so it's true to say that the motion about the sun is the dominant factor in the Moon's motion in the solar system. In a similar way, the Sun's motion around the Galactic Centre is greater than the Earth's motion about the Sun, but it's still true to say the Earth orbits the Sun.

2) The expansion of the universe is negligibly small on the scale of the solar system - the Earth's orbit about the sun should grow something like a few nanometres per hour. The force of gravity is more than strong enough to overwhelm such a minuscule perturbation. Only in the vast open spaces of the universe where gravity is negligibly weak does the expansion manifest.

## 1. What is the current understanding of the moon's orbit?

The moon's orbit around Earth is not a perfect circle, but rather an ellipse. This means that the distance between the moon and Earth varies as it orbits. The moon's orbit also has a slight tilt, causing it to appear to move higher or lower in the sky throughout the year.

## 2. How do scientists measure the moon's orbit?

Scientists use a variety of methods to measure the moon's orbit, including radar and laser ranging, lunar laser ranging, and satellite-based measurements. These measurements help track the moon's position, velocity, and distance from Earth over time.

## 3. What is the current understanding of the expansion of the universe?

The current understanding is that the universe is expanding at an accelerating rate, meaning that the distance between galaxies is increasing over time. This expansion is driven by a mysterious force called dark energy, which makes up about 70% of the universe.

## 4. How do scientists study the expansion of the universe?

Scientists use a variety of methods to study the expansion of the universe, including measuring the distances and velocities of galaxies, observing the cosmic microwave background radiation, and studying the properties of supernovae. These methods help us understand how the expansion of the universe has changed over time.

## 5. What implications does the moon's orbit and the universe's expansion have on our understanding of the universe?

Studying the moon's orbit and the universe's expansion can help us understand the fundamental laws of physics and the structure of the universe. It can also provide insights into the origin and fate of the universe, as well as how it may continue to evolve in the future.

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