As you are looking into the nighttime sky, you look into the depths of space. However, you are also looking into the depths of time.
Light takes its time traveling from one place to another. I can still remember the number my old seventh-grade science teacher forced us to memorize. Light travels at 186,282 miles per second. That’s 299,792 kilometers per second for those of you who think in meters per second.
The startling conclusion is that as far as our visual perception is concerned, there is no “now.” The present is a pleasant illusion, even for objects just a few inches from us. The farther away an object is, the farther back in time we are seeing.
Here’s something that you can do on Tuesday, Jan. 26, at about 10:30 p.m. EST to illustrate the point. Come to think of it, you can do it just about any time. It’s just that on that date, the objects in question are conveniently placed to do it all at once.
Stare up that evening at the mottled surface of the moon, which will be just a few days past full. The light you see is, of course, light reflected from the sun. After it bounces, the light takes a bit over one second to get to your eyes.
The moon’s surface is, in fact, rather dull and rather small. At only 2,000 miles wide, it reflects light with the efficiency of asphalt. Its proximity is its most telling feature. At only about a quarter of a million miles away, it shines most brightly in our earthly sky.
To the right of Luna is bright Jupiter. The planet is enormous at around 89,000 miles wide, and its cloud tops are very reflective – though not so shiny as those of, say, Venus. Its relative dimness compared to the moon is a simple matter of distance. At just over half a billion miles away, the light from the planet took about 45 minutes to get to Earth.
At a mere 45 light minutes away, we have already entered alien space. Earth and Luna are tiny balls of rock and metal. Jupiter is a gigantic, distended ball of liquid. It seems odd to even class them together in the same category.
And in an almost perfect line with the two planets, slightly up and to the right, will be the star that we call Regulus. The “little king” is the 22nd brightest star in the sky at 79 light years away. In a simple sweep of the eye, our use of light seconds and minutes as a measure of distance becomes insignificant. Regulus is a human lifetime away, and it is one of the closer stars to our sun and Earth.
But even a human lifetime as a measure of distance and time is reduced to a triviality. Just setting in the west is M31, an insignificant oval, fuzzy patch in the constellation Andromeda. The Great Andromeda galaxy is 2.5 million light years away. The light that most of you have seen many times began its journey before humanity existed as a species.
With the Andromeda Galaxy, we have reached the distance limit of normal human vision. Time to break out our telescopes. To the left of Jupiter, buried deeply within the confines of the constellations Virgo and Coma Berenices, is a cluster of hundreds of “island universes” like the Andromeda galaxy. The brightest one is M87. The light that you are seeing faintly in your telescope traveled 65 million years to get to you. As the light from hundreds of billions of stars began its long journey, dinosaurs were disappearing from the Earth.
Light travels at 186,282 miles per second. The number didn’t mean much to me when I was 13. It means much more to me now.
And thus it is that, if I live so long, I will go outside some fine spring morning when I am 79 years old. I will look at the constellation Leo rising majestically in the east. I will locate the bright star Regulus, and consider this simple fact: The light that I am seeing erupted from the surface or the star on or near the day that I was born.
That light has traveled my entire lifetime to strike my retina, and then it is gone forever. Afterward, it will exist only in my memory. That light will be just for me.
It will remind me of how much I have loved the stars and my often-inadequate efforts to help others to find that love within themselves.
It will remind me that we inhabit our planet for but a brief instant, and then we are gone. We must make the most of every moment so that perhaps we also may linger for a brief time in the memory of those who come after.
Tom Burns is director of the Perkins Observatory in Delaware.