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

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Discussion Overview

The discussion revolves around the Moon's orbit in relation to Earth, specifically addressing whether the Moon is moving closer or farther away over time. Participants explore the nature of the Moon's orbit, its elliptical characteristics, and the implications of recent observations regarding its proximity to Earth.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants note that the Moon's orbit is elliptical and that it can appear closer or farther from Earth at different times.
  • There is mention of a specific event where the Moon was reported to be the closest to Earth in 15 years, coinciding with a full moon.
  • One participant suggests that the Moon follows an approximately 18-year cycle, which influences its distance from Earth.
  • Another participant specifies that the Moon is receding from Earth at an average rate of 3.8 centimeters per year, but this is overshadowed by significant variations in perigee distance.
  • The timing of perigee is said to depend on the phase of the Moon, with local minima occurring at full and new moons.

Areas of Agreement / Disagreement

Participants express varying views on the Moon's orbit and its distance from Earth, indicating that multiple competing perspectives remain. There is no consensus on the implications of the Moon's movement or the significance of the reported proximity.

Contextual Notes

The discussion includes assumptions about the Moon's orbital mechanics and the influence of its elliptical orbit on distance variations, but these assumptions are not fully explored or resolved.

ADunn
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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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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.
 
Yeah, I seem to recall hearing that it was a full moon coinciding with perigee (or something like that)...
 
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:
 
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.
 

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