Moon's Orbit: Moving Closer or Farther From Earth?

In summary: During the full and new Moon phases, the tidal forces from the Sun and Moon reinforce one another, causing larger than average tides, known as "spring tides". This has the effect of increasing the Moon's distance at perigee. Conversely, during the first and third quarter phases, the tidal forces from the Sun and Moon are in opposition, causing smaller tides, known as "neap tides". This has the effect of decreasing the Moon's distance at perigee.In summary, the moon's orbit is elliptical and follows an approximately 18-year cycle. The moon is currently receding from the Earth at a rate of 3.8 centimeters per year, but this is not noticeable to the human eye.
  • #1
ADunn
6
0
It was reported that the Dec 12th moon was the closest it has been to Earth in 15 years. I've always heard that the moon is actually moving away from the Earth. Is the moon in a specific orbit? Or does its orbit change and if so, does it change in a specific way?
 
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  • #2
The moon's orbit is elliptical. I believe the statement is that this is the closest it has been in 15 years when it is full. It's hard to tell - the popular press has it kind of mangled.
 
  • #3
Yeah, I seem to recall hearing that it was a full moon coinciding with perigee (or something like that)...
 
  • #4
Welcome to PF!

ADunn said:
It was reported that the Dec 12th moon was the closest it has been to Earth in 15 years. I've always heard that the moon is actually moving away from the Earth. Is the moon in a specific orbit? Or does its orbit change and if so, does it change in a specific way?

Hi ADunn! Welcome to PF! :smile:

The Moon is on an approximately 18-year cycle.

(That's why eclipses repeat approximately every 18 years … but not visible at the same longitude on the Earth :wink:)

It was probably the same distance 33 years ago, and 51 years ago, and so on.

The Moon isn't moving away fast enough for anyone to notice. :smile:
 
  • #5
It's an 18.61 year cycle, to be a bit more precise. The Moon is receding from the Earth at 3.8 centimeters/year on average. The huge variation in the perigee distance, 13,000 miles, completely overwhelms this tiny drift rate.

The timing of perigee and the perigee distance depends in part on the phase of the Moon. The perigee distance exhibits local minima at full and new Moon.
 

1. What is the Moon's orbit?

The Moon's orbit refers to the path it takes around the Earth in space.

2. Is the Moon's orbit changing?

Yes, the Moon's orbit is constantly changing due to various factors such as gravitational pull from other celestial bodies.

3. Is the Moon moving closer or farther from Earth?

The Moon's orbit is gradually increasing in size, causing it to move about 3.8 cm farther away from Earth each year.

4. Will the Moon eventually move too far from Earth?

Yes, scientists predict that in about 50 billion years, the Moon will reach a point where its orbit will stabilize and it will no longer move farther from Earth.

5. How does the Moon's orbit affect Earth?

The Moon's orbit has a significant impact on Earth's tides and can also affect the length of Earth's day and the stability of its rotation.

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