HS #105 2024.4.11
The Solar Eclipse and Cosmic Distances
Did you experience the recent solar eclipse? Have you ever considered how special such an event is? Not because it happens only every few years, but because it happens at all.
The moon and sun are just the right sizes and just the right distances from earth that the apparent size of the moon is exactly the apparent size of the sun. This allows, during a total eclipse, for the moon to fully block out the sun, while still allowing us to see – and hence study – the solar flares which emanate from the surface of the sun.
Since the sun is roughly 400 times farther away from us than the moon, that means (via a simple proportion) that the sun’s distance across (its diameter) is roughly 400 times larger than the diameter of the moon. Since an object’s volume is gotten by multiplying its length by itself three times, this means that the sun is 400 x 400 x 400 = 64,000,000 times larger than the moon.
This serendipitous relationship was critically important in verifying one of the greatest scientific discoveries of all time – the General Theory of Relativity postulated by Einstein in 1915. Essentially, Einstein realized that space is like a fabric of cloth and heavenly bodies sitting on it cause it to stretch and deform: “Matter tell space how to curve, and space tells matter how to move.”
Most scientific discoveries are achieved by first observing a natural phenomenon and then trying to explain it. Not with Einstein. He thought it all out and only THEN was it observed. If his theory were correct, a massive object would slightly bend light – enough to be measured. Our sun is the handiest massive object around, so we can determine if light from stars on the other side of the sun will bend as it passes by. However, the only time we can see stars on the other side of the sun is when the light from the sun is blocked - during a solar eclipse. Cool! Einstein’s discovery was crucial for accurate GPS location measurements.
Since we’re pondering celestial bodies, let’s get an appreciation for the distances involved. The International Space Station orbits earth only 225 miles above us, the distance to the Mackinac Bridge. However, satellites which relay phone messages must move in sync with the earth’s rotation, so they are 100 times farther up – 22,000 miles. That’s one tenth the distance to the moon – 250,000 miles – or 10 times around the earth.
As noted above, the sun is about 400 times farther away from us than the moon – 93 million miles to be exact.
When you get to those vast distances, we need a more convenient way of expressing them. The easiest way is by using the speed of light as a measuring stick. Light travels fast enough to go around the earth seven times in a second. So it takes 1 1/2 seconds to get to the moon and 8 ½ minutes to get to the sun.
Using this same measuring stick, the next closest star to us takes light 4 years. On the other hand, to get to the nearest galaxy (other than our own Milky Way Galaxy) requires light traveling 25,000 years.
How close are the heavenly bodies to each other? This may surprise you: If your hand were the size of a star, the next nearest star would be 500 miles away – the distance from Holland to Nashville, TN. However, if your outstretched hand were an entire galaxy, then the next nearest galaxy is the distance to your other hand.
The immensity of the universe can’t be grasped. If the universe were the size of the earth, our earth would be smaller than an atom.
This led the theologian/astrophysicist, Christopher Kaiser, to pose the question: Which is the real drama? Is it the evolution of the universe, with the rise of life on earth and the history of humanity being a mere curiosity, a freak sideshow doomed to extinction and oblivion? Or is the story of humanity the real drama with the vast panorama of the universe there merely as a background?
3000 years ago a shepherd boy pondered the same when watching his flock under the night sky: “When I observe the work of Thy fingers, the moon and stars which Thou has ordained – what is Man that Thou art mindful of him?”
Interesting. As Immanuel Kant noted, for us humans, gazing outwards causes us to gaze inwards.
