Register to reply

Moon's Orbit

by ADunn
Tags: moon, orbit
Share this thread:
ADunn
#1
Dec14-08, 01:26 PM
P: 6
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?
Phys.Org News Partner Astronomy news on Phys.org
Magnetar discovered close to supernova remnant Kesteven 79
Image: Hubble looks at light and dark in the universe
Mixing in star-forming clouds explains why sibling stars look alike
Vanadium 50
#2
Dec14-08, 01:51 PM
Mentor
Vanadium 50's Avatar
P: 16,386
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.
cepheid
#3
Dec14-08, 01:56 PM
Emeritus
Sci Advisor
PF Gold
cepheid's Avatar
P: 5,196
Yeah, I seem to recall hearing that it was a full moon coinciding with perigee (or something like that)...

tiny-tim
#4
Dec14-08, 02:01 PM
Sci Advisor
HW Helper
Thanks
tiny-tim's Avatar
P: 26,148
Smile Moon's Orbit

Quote Quote by ADunn View Post
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!

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 )

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.
D H
#5
Dec14-08, 02:25 PM
Mentor
P: 15,173
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.


Register to reply

Related Discussions
General Relativity and the Moon's orbit. Special & General Relativity 2
Moon's orbit & length of day/month Astronomy & Astrophysics 1
Orbit Transfer to Lower Apoapsis of a Mars Orbit Introductory Physics Homework 11
Moon's orbit Astronomy & Astrophysics 15
Moon's orbit. Astronomy & Astrophysics 7