From "At the Heart of a Trillion Worlds" [1986]
Carl Sagan (1934-1996)
The ancients imagined the planets to be attached to invisible machinery--transparent crystal spheres, elegantly coupled and geared. We now know that the ancients were wrong. The planets orbit the Sun guided only by the invisible hand of Newtonian gravitation. Some worlds are rock, some gas, some ice, and nowhere, from Mercury to Pluto, is there anything like a crystal sphere. But imagine ourselves leaving the solar system at some impossible speed, until even the orbits of the outermost planets are too small for us to see, until even the Sun is only a point of light no brighter than the brightest stars seen from Earth. Then we do encounter something like a crystal sphere, but a shattered one--a cloud of a trillion shards and fragments of ice, little worlds each the size of a city, feebly illuminated in the great dark between the stars.
We live at the heart of a trillion worlds, all of them invisible. It sounds like the teaching of some New Age sect. And we are not talking of metaphorical worlds; rather a trillion places, every one of them as distinct a world as ours is, every one gravitationally bound to the Sun, every one with a surface and an interior and on occasion even an atmosphere.
If there is a ceiling above you, step outside. Cast your eye upward. Concentrate on the smallest piece of sky you can make out. Imagine it extending in a widening wedge far out into space, to the stars. In that little patch of sky are a hundred thousand worlds or more, worlds unseen, unnamed, but in some sense known. These distant cousins of the Earth are the cometary nuclei--cold, silent, inactive, slowly tumbling in the interstellar blackness. But when they are induced to fall into our part of the solar system, they creak and rumble, begin to evaporate and jet, and eventually produce the tails so admired by the inhabitants of Earth. How we know of this invisible multitude of icy worlds is one more scientific detective story, one of the many that begin with Edmond Halley.
Questions for Discussion
1. The phrase "crystal sphere" has the effect of
A) summarizing the key ideas
B) recalling a previous explanation
C) introducing a new topic
D) providing an additional example
E) none of the above
2. The phrase "shards and fragments" reinforces an image of
A) broken glass
B) smashed pottery
C) puzzle pieces
D) dust particles
E) none of the above
3. The image of "the great dark between the stars" is repeated later in what phrase?
A) "the heart of a trillion worlds"
B) "a ceiling above you"
C) "that little patch of sky"
D) "the interstellar blackness"
E) none of the above
4. What characteristic of the worlds is emphasized in the last paragraph?
A) age
B) size
C) number
D) distance
E) none of the above
5. In the last paragraph, the word "ceiling" refers to a barrier which is primarily
A) physical
B) mental
C) emotional
D) social
6. What word in the last paragraph is used to mean "propel"?
A) tumbling
B) creak
C) rumble
D) jet
E) none of the above
7. A recurring idea in this passage is that much of the known universe is
A) silent
B) invisible
C) fragile
D) expanding
E) none of the above
1B; 2A; 3D; 4C; 5A; 6D; 7B