Seeing the Sky as a Copernican

Why is perceiving the world that science describes often so difficult?

Posted Aug 05, 2017

Source: wikicommons

Carbondale’s First of Two (Almost Full) Days in the Sun

          Carbondale, Illinois is arguably the preeminent location in the United States for viewing the solar eclipse on August 21.  That is not only because it is in the path of greatest duration (about two and a half minutes) for the sun’s total eclipse.  Nor is it even because of the considerable support that Southern Illinois University, which is located there, is providing visitors who wish to view the eclipse.  Carbondale’s prominence derives, finally, from the fact that it will also be in the path of the next total eclipse of the sun in the USA on April 8, 2024.  It is, as one of the local slogans goes, the “Eclipse Crossroads of America.”  This means, among other things, as Nicholas St. Fleur has noted, that scientists will be able to carry out observations there that will permit comparisons of the sun’s corona over time.

Seeing and Understanding Astronomical Phenomena

          Looking directly at the sun, even when it is mostly occluded by the moon during an eclipse, is extremely dangerous.  It can damage viewers’ eyes permanently and cause blindness, and because retinal cells do not register heat, viewers will not even realize that they are injuring their eyes.  (Ultraviolet protective sunglasses will not prevent such damage!)

          Seeing the eclipse is fraught, but understanding the eclipse is not too difficult.  The moon moves between the sun and the earth.  Although it is much smaller than the sun, it is also much closer to the earth, so that it can completely occlude the sun, if viewed from the right angle.   Along the relevant, roughly 70-mile wide path on the earth, the moon’s shadow briefly turns day into night.  

          Nothing about the basic arrangements of an eclipse is counter-intuitive.  Consequently, this infrequent phenomenon is, ironically, much easier to see and to comprehend than are the everyday circumstances of our planet.  Its longstanding and widespread acceptance notwithstanding, the Copernican conception of the solar system is, by contrast, radically counter-intuitive.  Although Copernicus’ heliocentric theory has reigned for roughly four hundred years, it is, in fact, quite difficult to see the sky as a Copernican, as our persisting “sunrise” and “sunset” talk attests.

Robert McCauley
Source: Robert McCauley

We Are All Copernicans

          To do so requires some intellectual work.  Try this at dusk — ideally while on a beach looking westward across a large body of water.  Simultaneously construe the earth as a large, rotating globe that, on the same plane as the visible planets, is circling the disappearing sun.  To ascertain that plane, find Venus, which is the first heavenly body that is visible in the night sky.  It is not too far above the western horizon.  Envision it and the earth as both revolving around the sun on the same plane.  The sun continues to illuminate one-half of the moon (where we can only see some fraction of that illuminated area), which we know circles the earth at a distance that is much less than the distances between the earth and either the sun or the visible planets.  Keeping all of this in mind, by simply tilting your head so that it is perpendicular to the plane of the planets’ revolutions around the sun (rather than perpendicular to the surface of the earth), you can feel as if you are losing your balance because you recognize that you are (seemingly impossibly!) sticking out from the side of a massive earth.  Even if to no one else, to yourself you will seem to be unsupported.  If you do tumble, the beach’s sand is a comparatively safe place to fall.  That tumble too is a function of humans’ natural inclinations to orient themselves relative to the surface of the earth.

          The obvious point is that this is not the way that we naturally see the sky or see ourselves in the world.  To see the sky as a Copernican is an intellectual accomplishment no less than learning how to see an X-ray or a sonogram is.  Seeing some things about the world that our science describes depends upon careful conscious reflection influencing our perception.   Substantial familiarity with the Copernican theory does not obviate the fact that it, like most of science, is contrary to various of our natural perceptual and cognitive biases.


Churchland, Paul M.  (1979).  Scientific Realism and the Plasticity of Mind.  Cambridge:  Cambridge University Press

McCauley, Robert. N.  (2011).  Why Religion Is Natural and Science Is Not.  New York:  Oxford University Press.