By J Hugh Pruett, Astronomer, University of Oregon
When we look into the blue firmament of stars, we seem to see all its celestial jewels set at about the same distance from us, and really quite near. Some of the ancient astronomers were sure these heavenly bodies were far away, but not until recent methods of measurement were applied did we know the true spatial relationship of the various members of the universe.
Of all the sky luminaries, meteors and northern lights are the nearest, being merely in the upper atmosphere. Meteors, when visible, are usually less than 100 miles above the earth. Auroras may extend upward a few hundred miles.
Earth is attendant
Next comes our moon, which goes around the earth at a quarter million miles from us in a little less than a month. The earth, in turn, holding its constantly encircling moon, makes an annual trip around the huge, fiery sun at a mean distance of 93,000,000 miles.
But the earth is only one of the planets revolving around the sun Mercury and Venus go around on orbits nearer the sun than the earth. Farther out than are we there revolve in order Mars, Jupiter, Saturn, Uranus, Neptune and Pluto, the last at almost 40 times the earth’s solar distance. The tiny planets (asteroids), the orbits of 1564 of which have been calculated, and comets also circulate in this general space.
The above-mentioned bodies constitute the far-flung solar system enormous in extent, but relatively “invisible” in the mighty cosmic scheme. The sun is a star, appearing large because it is so near but it is only one of the estimated 30 to 100 billion stars in our vast star system, or galaxy.
The next nearest star known is 270,000 times farther from us than the sun. Our star with its planetary family is therefore most “lonesomely” isolated in the great sea of space.
Light takes about 10 hours to cross the huge orbit of Pluto, but it requires 100,000 years to span our enormous galaxy of stars. But even this galaxy is a relatively small part of the universe.
Limit of universe
The faint objects often called spiral nebulas, are now known to be exceedingly distant galaxies of billions of suns each. And it is estimated that there are millions of these galaxies so far apart that a light ray requires well toward a million years to cross the wilderness of space between any two of them.
Where are the limits of the universe? Our telescopes show none. The poet Poe once speculated that beyond our universe nothing exists which can never be comprehended by mortal mind.
“There may be other universes beyond,” he wrote, “but if so, they are ruled by an absolutely different set of natural laws; yea, even by entirely different gods.”