one of the individual parts making up a composite entity
But presently our journey takes us to what astronomers on Earth like to call the Local Group of galaxies. Several million light-years across, it is composed of some twenty
It is a
sparse and obscure and unpretentious cluster.
a star that explodes and becomes luminous in the process
Some stars, the
supernovae, are as bright as the entire galaxy that contains them; others, the black holes, are invisible from a few kilometers away.
turn into gas
Every now and then a passing star gives a tiny gravitational tug, and one of them obligingly careens into the inner solar system. There the Sun heats it, the ice is
vaporized, and a lovely cometary tail develops.
originating, located, or occurring outside Earth
And on the countless other planets that may circle other suns, is there life also? Is
extraterrestrial life, if it exists, based on the same organic molecules as life on Earth?
a musical form consisting of a repeated theme
Or is there a kind of cosmic
fugue, with themes and counterpoints, dissonances and harmonies, a billion different voices playing the life music of the Galaxy?
hard outer covering or case of certain organisms
How does it come about that the face of a warrior is incised on the
carapace of a crab? The answer seems to be that humans made the face. The patterns on the crab’s shell are inherited.
having a capacity for change
The secrets of evolution are death and time—the deaths of enormous numbers of lifeforms that were imperfectly adapted to the environment; and time for a long succession of small mutations that were by accident
adaptive, time for the slow accumulation of patterns of favorable mutations.
characteristic of an earlier ancestral type
In those early days, lightning and ultraviolet light from the Sun were breaking apart the simple hydrogen-rich molecules of the
primitive atmosphere, the fragments spontaneously recombining into more and more complex molecules.
the simplest structural unit of an element or compound
This was the earliest ancestor of deoxyribonucleic acid, DNA, the master
molecule of life on Earth.
a complex protein produced by cells that acts as a catalyst
Since mutations are random nucleotide changes, most of them are harmful or lethal, coding into existence nonfunctional
the governing authority of a political unit
The living cell is a
regime as complex and beautiful as the realm of the galaxies and the stars.
having a relatively high resistance to flow
During reproduction, the helices separate, assisted by a special unwinding protein, each synthesizing an identical copy of the other from nucleotide building blocks floating about nearby in the
viscous liquid of the cell nucleus.
of organisms living together, especially to mutual advantage
This points to a long evolutionary separation of the genetic codes of mitochondria and nuclei, and is consistent with the idea that mitochondria were once free-living organisms incorporated into the cell in a
symbiotic relationship billions of years ago.
a force that makes something happen
If we lived on a planet where nothing ever changed, there would be little to do. There would be nothing to figure out. There would be no
impetus for science.
a language user's knowledge of words
We today can recognize the antiquity of astrology in words such as disaster, which is Greek for “bad star,” influenza, Italian for (astral) “influence”; mazel tov, Hebrew— and, ultimately, Babylonian—for “good constellation,” or the Yiddish word shlamazel, applied to someone plagued by relentless ill-fortune, which again traces to the Babylonian astronomical
not restricted to one school or party
Almost half of our national flags exhibit astronomical symbols. The phenomenon is transcultural,
requiring secret or mysterious knowledge
arcane business about planets ascendant in this or that solar or lunar “house” or the “Age of Aquarius” comes from Ptolemy, who codified the Babylonian astrological tradition.
the branch of theology that is concerned with final things
He wished to learn the
eschatology of the world; he dared to contemplate the Mind of God.
patent medicine whose efficacy is questionable
Superstition was a widely available
nostrum for people powerless against the miseries of famine, pestilence and deadly doctrinal conflict.
a closed plane figure bounded by straight sides
There were known to be five regular or “platonic” solids, whose sides were regular
polygons, as known to the ancient Greek mathematicians after the time of Pythagoras.
the farthest point in an orbit around the Earth
He would only, in the course of a meal and, in between other matters, mention, as if in passing, today the figure of the
apogee of one planet, tomorrow the nodes of another ...
facts learned by watching attentively
After Tycho’s death, Kepler, now the new Imperial Mathematician, managed to extract the
observations from Tycho’s recalcitrant family.
a closed plane curve with an oval shape
Kepler’s first two laws may seem a little remote and abstract: planets move in ellipses, and sweep out equal areas in equal times.
point formed by two intersecting arcs
Kepler stood at a
cusp in history; the last scientific astrologer was the first astrophysicist.
(of weather or climate) not mild; subject to extremes
Because of the length of the lunar day and night Kepler described “the great intemperateness of climate and the most violent alternation of extreme heat and cold on the Moon,” which is entirely correct.
acting along a straight line or plane that touches a curve
The Moon, it seemed to Newton, would fly off in a straight line,
tangential to its orbit, unless there were some other force constantly diverting the path into a near circle, pulling it in the direction of the Earth.
mass consisting of antiparticles of normal substances
This remarkable occurrence is called the Tunguska Event. Some scientists have suggested that it was caused by a piece of hurtling
antimatter, annihilated on contact with the ordinary matter of the Earth, disappearing in a flash of gamma rays.
the striking of one body against another
But the absence of radioactivity at the
impact site gives no support to this explanation.
maintain or assert
postulate that a mini black hole passed through the Earth in Siberia and out the other side.
an event indicating important things to come
So the idea arose that comets were harbingers of disaster,
auguries of divine wrath—that they foretold the deaths of princes, the fall of kingdoms.
an inclination to interpret statements in a particular way
The featureless clouds of Venus reflected our own
predispositions. We are alive, and we resonate with the idea of life elsewhere.
the act of gathering up
But only careful
accumulation and assessment of the evidence can tell us whether a given world is inhabited.
extremely harmful; bringing physical or financial ruin
On Venus, on Earth and elsewhere in the solar system, there is evidence for
catastrophic destruction, tempered or overwhelmed by slower, more uniform processes
relating to deposits carried by rushing streams
on the Earth, for example, rainfall, coursing into rivulets, streams and rivers of running water, creating huge
alluvial basins; on Mars, the remnants of ancient rivers, perhaps arising from beneath the ground; on Io, a moon of Jupiter, what seem to be broad channels made by flowing liquid sulfur.
relating to or resembling or derived from glass
But we did not want to land in a place that was too hard either—had we landed in a
vitreous lava field, for example, with no powdery surface material, the mechanical arm would have been unable to acquire the samples vital to the projected chemistry and biology experiments.
originating where it is found
Vishniac believed that the experimental techniques previously used to deduce no
indigenous microbes in Antarctica were flawed.
any substance that can be metabolized to give energy
nutrients, while suitable for the comfortable environment of a university microbiology laboratory, were not designed for the arid polar wasteland.
become weaker, in strength, value, or magnitude
On Mars such a place would be even more interesting, because while the visible light necessary for photosynthesis would penetrate to that depth, the germicidal ultraviolet light would be at least partially
produce by the organic processes necessary for life
First, when Martian soil was mixed with a sterile organic soup from Earth, something in the soil chemically broke down the soup—almost as if there were respiring microbes
metabolizing a food package from Earth.