Hundreds of moons, planets and other bodies in the Solar System, and only ours — Earth and the Moon — have perfect solar eclipses. Astronomers have long noted this strange phenomenon, and the unlikely parameters that cause it. Not only that, but they happen to occur in a time in Earth’s history where they can be observed. Astronomer John Gribben writes:
Just now the Moon is about 400 times smaller than the Sun, but the Sun is 400 times farther away than the Moon, so that they look the same size on the sky. At the present moment of cosmic time, during an eclipse, the disc of the Moon almost exactly covers the disc of the Sun. In the past the Moon would have looked much bigger and would have completely obscured the Sun during eclipses; in the future, the Moon will look much smaller from Earth and a ring of sunlight will be visible even during an eclipse. Nobody has been able to think of a reason why intelligent beings capable of noticing this oddity should have evolved on Earth just at the time that the coincidence was there to be noticed. It worries me, but most people seem to accept it as just one of those things.
Even if we brush this off as coincidence, as some have tried to do, there is another layer to this. Many of the interconnected factors that allow the eclipse to occur, also allow life to exist on Earth.
Sizes of the Moon and the Earth, distance from each other, size and distance of Sun, rotation rates, revolution rates, and so on. These all impact whether or not life survives — or can appear to begin with — on the blue planet along with hundreds of other terrestrial and celestial factors. If you crunch the numbers, chance cannot explain this, which leads to much philosophizing and hand-ringing. Those who don’t like the implications of astronomy — that we aren’t just an unimportant, pale blue dot — have a hard time explaining this all away (like this scientist who thinks repeating “coincidence” as much as possible is a scientific argument).
Regardless of one’s beliefs, the physics behind eclipses can both inspire more scientific inquiry and thoughtful discussion on our place in the universe. In these times of constant political and social mayhem, maybe we can use this eclipse for more than a break from work, but a time to think deeper. Astronomer Guillermo Gonzalez, in his groundbreaking book on this subject, The Privileged Planet, wrote this:
The same rare conditions that have sustained our existence also make possible a stunning array of discoveries about the universe…Because of it, and only because of it, can our aspirations of scientific knowledge and discovery be satisfied…With enough persistence, the natural world discloses itself to us in ways that we do not, and sometimes cannot, anticipate. Once perceived, the thought creeps up quietly but insistently: The universe, whatever else it is, is designed for discovery. What better mandate could there be for the scientific pursuit of truth? Scientific discovery enjoys a sort of cosmic prestige, but a prestige apparent only to those open to the possibility that the cosmos exists for a purpose.