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Stargazing Last nights total Lunar eclipse

  1. Aug 28, 2007 #1


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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.

  2. jcsd
  3. Aug 28, 2007 #2
    Very cute. Is that to scale? Where did you obtain the image data?
  4. Aug 29, 2007 #3
    thank you about this information

    I like this information

    the Moon's orbital speed changes >> size changes >> orbital speed changes = the moon dances
  5. Aug 29, 2007 #4


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    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.
  6. Aug 29, 2007 #5

    Is THAT what the moon looks like? :)
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