23 Aug 07 1 billion light-years to 0.1 fermi

从10亿光年到0.1飞米

about 1 billion light-years, 10²⁵ meters

Most of space looks as empty as this, the glow of distant galaxies like dotted dust. This emptiness is normal; our own bright home-world is the exception. A tenfold larger view would show no new structure, no new void; the universe is roughly uniform at such dimensions. Novelty on so grand a scale is to be sought over time rather than from place to place. All swift change is in the past. This view will dim slowly, for a few billion years at least, as the faint clusters drift still farther apart.

about 100 million light-years, 10²⁴ meters

We look toward our distant home in the Milky Way. But we see mostly one large intervening cluster of galaxies, called the Virgo Cluster. Galaxies as a rule associate into orbiting clusters and groups. There is reason to believe that our Milky Way is itself an outlier of the big Virgo Cluster, responsive to its steady gravitational pull: part of a supercluster. Out there beyond the Milky Way is a good-sized volume nearly devoid of noticeable galaxies.

about 10 million light-years, 3 megaparsecs, 10²³ meters

These are the galaxies of our own cosmic region, each single bright spot made by the summed light of stars by the billion. Their mutual gravity binds stars into galaxies, every one a complex swarm of moving stars.

about 1 million light-years, 10²² meters

This flat circular disk is our own Galaxy, the Milky Way, with its spiral structure. It travels in space with two satellite galaxies, the irregular little Clouds of Magellan. Not many galaxies are larger than ours; nor are many seen that are smaller than the Clouds.

about 100 thousand light-years, 10²¹ meters

We look face-on directly at the Milky Way spiral. A hundred billion stars mutually bound by gravity encircle the central region, some passing close in, some in wider orbits. Our own sun swings with the rest in dignified passage clockwise about the distant galactic center, once every three hundred million years. External galaxies akin to our own are scattered throughout space as far as we can see. They too rotate slowly as they drift.

about 10 thousand light-years, 10²⁰ meters

Clouds of stars and glowing gas, with patches of darkening dust, mark the slow-changing spiral patterns of the Galaxy disk. Our distant sun cannot be seen here, but it is in the center of the image, near the border of one spiral arm.

about 1 thousand light-years, 10¹⁹ meters

In this view we are within the disk of the Galaxy, right among a host of stars visible here as individuals. Almost every star of the thousand mapped by the old watchers of the sky, those who first gathered stars into constellations, lies within this square, our own galactic neighborhood. There are many other stars as well, too faint for the eye to see.

about 100 light-years, 10¹⁸ meters

A skyful of distinct stars; One among them, central, but too faint to pick out, is our sun. The star Arcturus, prominent in the northern sky of earth, shines brightly. Arcturus is intrinsically more luminous than our sun, and here we are nearer to it as well.

about 10 light-years, 3 parsecs, 10¹⁷ meters

Most of the matter we know is formed into stars, spheres of gas nourished by central nuclear fires that often maintain the glow for a very long time. At this point in the journey, with no star nearby, we see the realm of the stars chiefly as a distant background, no different from the night sky we view from earth. For several frames the star background remains unchanged; The visible stars are strewn so deep in space that these steps are small in comparison. Hence they cause no noticeable shifts.

about 1 light-year, 10 trillion kilometers, 10¹⁶ meters

Here one central star is brighter than the rest, only because it is so much nearer. That star is the sun. The contrast between night and day, between the cold glitter of the starry sky and life-giving warmth, is the consequence simply of our planet’s location next to one modest star. Once we have drawn away from the sun, we can recognize that it is one star among many stars, and all distant stars are in some way suns.

1 trillion kilometers, 10¹⁵ meters

Only the sun is to be seen, against a background of fainter stars beyond. Once that was all we knew of the frontier of the sun’s system. We know now that a great cloud of icy comets orbits slowly here, though invisible in the weak sunlight. We see comets only as year after year a few fall into the brighter regions near earth. There we catch sight of them, moving in the sky like temporary planets, the sun’s fires boiling out their long faint tails.

100 billion kilometers

All the sun’s planets circulate within the small square. From earth the planets have always stood out, a few strange bright stars restlessly wandering in a skyful of unchanging patterns. Seen here from outside, the planets take on their Copernican aspect; they move around the sun on these nested ellipses, mapped by colored lines.

10 billion kilometers

The paths of the outer planets fill this picture. That strongly tilted orbit belongs to little, awry Pluto. The four others are those of big Neptune, Uranus, Saturn, and Jupiter, with their many satellites. Between Jupiter’s path and the sun run the inner planets in their smaller orbits. The planets circulate counterclockwise here, all in nearly the same plane, which we view at an angle; The planetary system, apart from Pluto, is flat as a pancake.

1 billion kilometers

Enclosed in the path of massive Jupiter, these are the orbits of the smaller earthlike inner planets: Mars, Earth, Venus, Mercury. Another swarm of objects too small and faint to make out without telescopic aid is present as well: asteroids and meteors ply this darkness in the belt between the orbits of Mars and Jupiter.

100 million kilometers

Now we see the inner solar system.The green arc is traversed by planct Earth during some six weeks each September and October.

10 million kilometers

This path marks the earth’s way for four days in October;within it the moon’s route is indicated relarive to earth.The moon at all times lies somewhere on that small ellipse which moves along with the earth in its orbit.

1 million kilometers

The farthest place our own kind has yet visited is the companion moon,our nearest celestial neighbor.Bright moonlight and the tides wimess her proximity.

100 thousand kilometers