alert(oSun.style.getExpression("left"));

We would have gotten the following alert box:

oSun.style.setExpression("left", "document.body.clientWidth / 2 -
  oSun.style.pixelWidth / 2");

And likewise for the moon, had we issued this line:

alert(oMoon.style.getExpression("left"));

we would have gotten:

oMoon.style.setExpression("left", "xLocation(oEarth, 0.1, 28, currentTime) - 
  oMoon.style.pixelWidth / 2");

For more on Dynamic Properties, go to Column 65, Dynamic Properties.

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