In their book the Privileged Planet, Astronomer Guillermo Gonzalez, Assistant Professor of Astronomy at Iowa State University, and Jay Richards, Vice President and Senior Fellow of the Discovery Institute in Seattle claim that the fact that the Sun and the Moon are almost identically the same relative size is a sign of Intelligent Design. The argument goes like this[1]:
Though the moon is 400 times smaller than the sun, it ‘happens’ to be 400 times closer than the sun. Thus their relative sizes in the sky are almost identical. Because of this we are able, during a solar eclipse, to observe the sun and other stars normally blotted out by the sun. Gonzalez studied 65 other bodies and concluded that on none of them would a total eclipse occur.
It is true enough that the Sun and the Moon are almost exactly the same relative size right now. It is also true enough that has not always been the case and will not be the case in the future.
Even during a calendar year the ratio changes a bit. The orbit of the Earth around the sun is not a perfect circle. It is instead an ellipse meaning that the exact distance from the Earth to the Sun varies – though it is close. A circle has an eccentricity of zero. The Earth's orbital eccentricity is 0.0167 meaning that the ratio of its semi-minor to semi-major axis is 99.99%[2]. That’s stable, but it would be obviously better if it was a perfect circle.
More relevantly, due to tidal effects, the Moon is gradually moving away from the Earth so that the relative size of the Moon is diminishing. In fact that has been taking place since the Moon was first created (an estimated 4.5 billion years ago).
We know this because we can measure it. Three Apollo missions (Apollo 11, 14 and 15) as well as two unmanned Soviet probes put laser reflectors on the Moon. The exact distance from the Earth to the Moon is measured by precisely measuring the time required for a laser beam to leave Earth, bounce off of the reflector and return to Earth. Based on these measurements, we know that the Moon is moving away from the Earth at the rate of 38 mm per year[3].
While there is a small amount of variation in the distance from the Moon to the Earth, the average distance from the Earth to the Moon is 384,467 kilometers. Therefore that distance is varying at the rate of very close to 0.1% per million years or 10% per billion years. While those are very long periods of time, over the 4.5 billion years that the Moon and Earth have moved relative to each other the current “perfect eclipses” would seem to be an accident of timing more than anything else.
In fact, if you use a strict definition of “perfect” even the relatively minor variations in the distances to the Sun and the Moon over a year render even current eclipses something other than “perfect”. Perfectly circular orbits would be a more “perfect” solution than elliptical orbits.
Besides, what’s the big deal?
[1] http://www.evidenceofdesign.com/privileged-planet/, retrieved on March 24, 2010. The web page lists a number of other similar “evidences” for Intelligent Design.
[2] http://en.wikipedia.org/wiki/Orbit, retrieved on March 24, 2010.
[3] Fred Espenak (August 1994). "NASA - Accuracy of Eclipse Predictions". eclipse.gsfc.nasa.gov. Retrieved June 4, 2008.
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