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The Stars beyond our Solar System

Sagittarius Star CLoud

The Sagittarius Star Cloud at the center of the Milky Way galaxy: Hubble Heritage Team (AURA/STScI/NASA)




Beyond the Sunís influence and its Oort cloud we enter the space between stars, interstellar space. Accompanied by their heavenly retinue of planets, asteroids, comets and debris, stars congregate in immense gravitational groups called galaxies. Ellipsoids, disks, and spirals tens to hundreds of thousands of light years in diameter and containing most of the visible matter in the universe, galaxies are made up of hundreds of billions to trillions of stars. And if we look towards the center of our own galaxy, we see the view above. Curiously enough, the color of a star indicates its temperature and its place in its life cycle. From hottest and youngest to oldest and coolest, star colors (followed by the associated "spectral type" in parentheses) are blue (O & B), white (A), yellow-white (F), yellow (G, like our Sun), orange (K), and red (M).

Although itís too early in our observational experience to give a percentage of the stars that have planets, that condition seems to be the rule rather than the exception. Most stars are probably also encircled by billons of small bodies like our asteroid and Kuiper belts that never coalesced into planets as the system evolved. And further out still is each starís own Oort cloud, a sphere of trillions of frozen objects left over from that systemís primordial past. By this point weíve come a few light years from the star and have reached the edge of itís gravitational and magnetic influence.

The distance light travels in a yearóa "light year," about six trillion milesóis the yardstick astronomers use for measuring large distances. Because other stars and galaxies are so far away, it takes time, and lots of it, for their "pictures" to get here. So as we look out into the universe, we are, by necessity, looking back in time. If, for example, the Sun exploded, we wouldnít know it for 8.3 minutes, because thatís how long it takes light to get to us from the Sun. Pluto is five light hours away, and the next nearest visible star, Alpha Centauri, is 4.4 light years distant.

Everything else we see in the night sky thatís not in our solar system is older still. The nearest galaxy to us, the Andromeda galaxy, is just under three million light years away. Thatís how old its picture is when we see a photograph of it. In fact, astronomers are now looking out so far into the universe (billions of light years) that they hope to see the universe begin, about 13.7 billion light years away and just that many years ago!

This Stars Beyond our Solar System page and much of this 600-page website are excerpted from the personalized Fine Art Book You and the Universe.

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© Carl Woebcke: Stars Beyond our Solar System, 1991-2017. All rights reserved.