Did You Know the Moon Dances for Us Every Month?

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Discussion Overview

The discussion revolves around the Moon's movements and characteristics, particularly focusing on its libration, orbital eccentricity, and the visual effects these have on its appearance from Earth. Participants explore the concept of the Moon's "dance" as it relates to its changing distance and speed, as well as the creation of an animation to illustrate these phenomena.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant describes the Moon's apparent size changes due to its varying distance during its orbit, noting that this is observable when comparing images taken at perigee and apogee.
  • Another participant mentions the Moon's orbital speed changes while its rotational speed remains constant, leading to libration effects that allow observers to see slightly different views of the Moon over time.
  • A participant highlights the tilt of the Moon's axis relative to its orbital plane, which causes its poles to appear to nod back and forth.
  • One participant expresses appreciation for the information shared and summarizes the relationship between the Moon's orbital speed and size changes as part of its "dance."
  • Another participant inquires about the scale and source of the animation, seeking clarification on whether the apparent size change and rotation are accurately represented.
  • A later reply confirms that the animation was created using a 3D computer model and describes the methodology used to generate it, including the application of orbital mechanics equations.

Areas of Agreement / Disagreement

Participants express curiosity and appreciation for the information shared, but there is no explicit consensus on the details of the Moon's movements or the accuracy of the animation. Questions remain regarding the scale and data sources used in the animation.

Contextual Notes

Some assumptions about the accuracy of the animation and the representation of the Moon's movements are not fully explored, and there are unresolved questions about the specifics of the image data used.

Janus
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Last nights total Lunar eclipse was probably the first time a great many people even paid any attention to our natural satellite for quite a while. It's kind of taken for granted. After all, except for the passing phases, it usually doesn't change. Its the same face staring at us night after night.

But did you know that the Moon does a little dance for us every month? All brought us by the eccentricity of its orbit.

First, the Moon's distance changes, and thus it's apparent size changes. Not very much but enough to notice if you compare pictures taken at perigee and apogee.

Then there's the fact that the Moon's orbital speed changes over its orbit, while its rotational speed remains the same. This causes one of the moon's librations, in which it seems to rock back and forth on its axis, thus affording us a peek around its limb.

The Moon's axis is also tilted slighty to its orbital plane, causing its North and South poles to nod back and forth to us.

Granted, it is a very sedate dance, taking some 27.3 days to complete a cycle. This is why I cobbled up this little animation, to allow us to enjoy this Moondance at a little quicker pace. In it, I decided to leave out the Moon's phases and keep the spotlight on the moon, so to say, so her dance could be seen in its full glory. I hope you enjoy it.

http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/moondance.gif
 
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Very cute. Is that to scale? Where did you obtain the image data?
 
thank you about this information

I like this information

the Moon's orbital speed changes >> size changes >> orbital speed changes = the moon dances
 
cesiumfrog said:
Very cute. Is that to scale? Where did you obtain the image data?

If by "to scale" you mean is the apparent size change and rotation accurate, then yes.

The animation was created using a 3D computer model (a Ray-tracing program). The surface features of the Moon where image-mapped onto a sphere. Then I used orbital mechanics equations to cause the sphere to trace out the Moons orbit, while the program's "camera" tracked the Moon from the orbit's focus.

By altering the parameters, I could generate an animation that would show how the Moon would appear with diffrent axial tilts, eccentricies or rotation rates, or, by changing the position of the program's "light source", I could have included the Moon's phases.
 
Janus said:
Last nights total Lunar eclipse was probably the first time a great many people even paid any attention to our natural satellite for quite a while. It's kind of taken for granted.

This is why I cobbled up this little animation, to allow us to enjoy this Moondance at a little quicker pace. In it, I decided to leave out the Moon's phases and keep the spotlight on the moon, so to say, so her dance could be seen in its full glory. I hope you enjoy it.

http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/moondance.gif

[/quote]

Is THAT what the moon looks like? :)
 
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