Orion rising in Death Valley - Credit: Ben Burress

What brings this on? Well, the skies of Death Valley, actually, which I just returned from (Death Valley, not its skies!) over the holiday break. My daughter and I went down there, mainly to crawl around the sand dunes and canyons, visit sites of the Gold Rush pioneers who gave the valley its [English] name, and get another good, up-close look at the raw Earth….

…but, as always, at night, when the campfire sparks warmly, I end up looking to the stars, which are extraordinarily bright in the dark desert skies. And I just get to thinking…again….

My touchstone on the vastness of the Universe is the knowledge that all the stars we can see in the night sky, with our unaided eyes, are quite starkly the closest things to us in the Universe—and even from those objects, light, traveling at 186,300 miles per second, takes years, decades, even centuries just to reach us. These "local neighborhood" stars are all within our Milky Way galaxy, and all among the very closest of them.

So, the stars of the night sky are a sort of "front drop"—like a big sheet of paper with stars printed on it, held before us–and the stars and galaxies of the rest of the Universe, beyond this "front drop," are too far away for our eyes to perceive their light (without the help of a telescope).

Trying to put the scale into perspective (trying very hard!), if this "sheet of paper" with stars printed on it, held in front of our collective Earthly "face", was, say, 1000 light years away (6000 trillion miles—which is actually about the greatest distance that our unassisted eyes can detect individual stars, and only stars of the most luminous type at that), this would be analogous in scale to an individual person holding a star-printed sheet of paper about two tenths of an inch before their eyes (yeah, I know, too close to focus on the printed stars…), with the surrounding Bay Area representing "the rest of the Universe."

What? I didn’t hear you…. What I said was, if the entire Bay Area represents the Universe, then the stars we can see with our eyes are found within two tenths of an inch of our eyeballs…. Even the Andromeda Galaxy, the most distant object unaided human eyes can perceive (and which I did spot as a very faint smudge on the dark Death Valley sky!), at a distance of about 2.5 million light years, would be less than 4 feet away from you in your Bay-Area-scaled Universe.

It’s here that my mind boggles, and it becomes doubtful to me that our brains have the capacity to really wrap around the Universal scale. It’s hard enough imagining the distances to the "nearby" local stars, a space in which light spends centuries crossing; trying to see beyond that big sheet of paper, to the 13.7 billion light year extent of space and time…boggle…fail….

So, the next time you find yourself gazing at the stars, remember that those are just the spots flittering around in front of our collective eyeball, no more than an eyelash away….

And if that makes you feel small, cheer up; you live in a Universe that is altogether astonishing and magnificent, and not just a run-of-the-mill Universe of comprehendible size. I feel honored and proud….

Centuries ago the stars were believed to reside just beyond the planets of our solar system.

How do we know how far away celestial objects are? This shouldn't be taken for granted, as it's not as straightforward as sounding the depth of the ocean floor with sonar, or determining the range to an object by bouncing radio waves off it and timing the reflection.

In fact, we have "pinged” the nearest celestial objects with radar to determine their distances very accurately. Examples are the Moon and Venus, where round-trip lightspeed travel is measured in seconds or minutes.

Before radar, the scale of the Solar System had to be determined geometrically, by observing events like Venus or Mercury transiting the face of the Sun from different locations on Earth and triangulating. Even this technique requires telescopes, which we've had only four hundred years. Before that, figuring out distances to just about everything except the Moon was mostly guesswork. In fact, it wasn't too many centuries ago that the entire Universe was believed to be not much larger than the Solar System—the Sun and it's nine…excuse me…eight planets—as we know it today.

Once the distance from Earth to the Sun was figured out, that length (the "Astronomical Unit”) in effect became a basic measuring rod for working out distances to everything else, by one means or another.

As Earth orbits the Sun, the direction from which we see stars shifts minutely, and we can observe a small change in a star's position compared to the more distant "background” stars. You can see the same effect by holding a finger in front of your face and looking at it alternately with one eye, then the other.

The geometry of this observation is a simple triangle, whose base is the distance between your eyeballs and whose legs are the lines from each eyeball to your finger. By knowing the length of the base, and observing the change in viewing angle against the background, the length of the legs (distance from your eyeballs) can be calculated.

In the case of Earth and a nearby star, the "eyeballs” are the Earth at two ends of its orbit around the Sun (six months apart) and the "finger” is the star.

But this measuring of distance by "trigonometric parallax," as it's called, only works for the nearest stars, as the minute shift in the star's apparent position diminishes with distance.

As astronomers learned more about the distance to nearby stars, they determined how to relate their temperature and mass to their actual brightness, and it became possible to estimate the distance of many stars by measuring their apparent brightness, with an understanding of how the brightness of light weakens with distance.

To measure the depths of space between us and galaxies far, far away, in which individual stars are indistinguishable from the overall galactic glow, we can turn to certain types of supernovae: individual stars that temporarily shine brightly enough to be observed and measured. Like the flare of a match struck in the dark night, the brilliance of the flash reveals how far away the striker stands.

We have built up our knowledge of the Universe's vastness over the past couple centuries, working out the problem from the near to the far. Even as science and technology have made the world on which we live smaller, it has done exactly the opposite to the Universe….

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