Origins: Fourteen Billion Years of Cosmic Evolution (30 page)

radio
:
Photons
with the longest
wavelengths
and lowest
frequencies
.

radioactive decay
: The process by which certain types of atomic
nuclei
spontaneously transform themselves into other types.

red-giant star
: A
star
that has evolved through its main sequence phase and has begun to contract its core and expand its outer layers. The contraction induces a greater rate of
nuclear fusion
, raises the star’s
luminosity
, and deposits energy in the outer layers, thereby forcing the star to grow larger.

red shift:
A shift to lower
frequencies
and longer
wavelengths
in the
spectrum
of an object, typically caused by the
Doppler effect
.

relativity:
The general term used to describe Einstein’s
special theory of relativity
and
general theory of relativity
.

replication
: The process by which a “parent”
DNA
molecule divides into two single strands, each of which forms a “daughter” molecule identical to the parent.

resolution:
The ability of a light-collecting device such as a camera, telescope, or microscope to capture detail. Resolution is always improved with larger lenses or mirrors, but this improvement may be negated by atmospheric blurring.

revolution:
Motion around another object; for example, Earth revolves around the Sun. Revolution is often confused with
rotation
.

RNA (ribonucleic acid)
: A large, complex molecule, made of the same types of molecules that constitute
DNA
, which performs various important functions within living cells, including carrying the genetic messages embodied in DNA to the locations where
proteins
are assembled.

rotation
: The spinning of an object on its own axis. For example, Earth rotates once every 23 hours and 56 minutes.

runaway greenhouse effect
: A
greenhouse effect
that grows stronger as the heating of a planet’s surface increases the rate of liquid evaporation, which in turn increases the greenhouse effect.

satellite
: A relatively small object that orbits a much larger and more massive one; more precisely, both objects orbit their common center of mass, in orbits whose sizes are inversely proportional to the objects’ masses.

self-gravitation
: The
gravitational forces
that each part of an object exert on all the other parts.

SETI
: The search for extraterrestrial intelligence.

shooting star
: A popular name for a
meteor
.

skepticism
: A questioning or doubting state of mind, which lies at the root of scientific inquiry into the cosmos.

Small Magellanic Cloud
: The smaller of the two
irregular galaxies
that are satellites of our
Milky Way
.

solar system
: The Sun plus the objects that orbit it, including
planets
, their
satellites
,
asteroids
,
meteoroids
,
comets
, and interplanetary dust.

solar wind
: Particles ejected from the Sun, mostly
protons
and
electrons
, which emerge continuously from the Sun’s outermost layers, but do so in especially large numbers at the time of an outburst called a solar flare.

solvent
: A liquid capable of dissolving another substance; a liquid within which
atoms
and
molecules
can float and interact.

space-time:
The mathematical combination of space and time that treats time as a coordinate with all the rights and privileges accorded space. It has been shown through the
special theory of relativity
that nature is most accurately described using a space-time formalism. It simply requires that all events are specified with space
and
time coordinates. The appropriate mathematics does not concern itself with the difference.

special theory of relativity:
First proposed in 1905 by Albert Einstein, this provides a renewed understanding of space, time, and motion. The theory is based on two “Principles of Relativity”: (1) the speed of light is constant for everyone no matter how you choose to measure it; and (2) the laws of physics are the same in every frame of reference that is either stationary or moving with constant velocity. The theory was later extended to include accelerating frames of reference in the
general theory of relativity
. It turns out that the two Principles of Relativity that Einstein
assumed
have been shown to be valid in every experiment ever performed. Einstein extended the relativity principles to their logical conclusions and predicted an array of unusual concepts, including:

• There is no such thing as absolute simultaneous events. What is simultaneous for one observer may have been separated in time for another observer.

• The faster you travel, the slower your time progresses relative to someone observing you.

• The faster you travel, the more massive you become, so the engines of your spaceship are less and less effective in increasing your speed.

• The faster you travel, the shorter your spaceship becomes—everything gets shorter in the direction of motion.

• At the speed of light, time stops, you have zero length, and your mass is infinite. Upon realizing the absurdity of this limiting case, Einstein concluded that you cannot reach the speed of light.

Experiments invented to test Einstein’s theories have verified all of these predictions precisely. An excellent example is provided by particles that have decay “half-lives.” After a predictable time, half are expected to decay into another particle. When these particles are sent to speeds near the speed of light (in particle accelerators), the half-life increases in the exact amount predicted by Einstein. They also get harder to accelerate, which implies that their effective mass has increased.

species
: A particular type of organism, whose members possess similar anatomical characteristics and can interbreed.

spectrum (
pl:
spectra)
: The distribution of
photons
by
frequency
or
wavelength
, often shown as a graph that presents the number of photons at each specific frequency or wavelength.

sphere:
The only solid shape for which every point on the surface has the same distance from the center.

spiral arms
: The spiral features seen within the disk of a
spiral galaxy
, outlined by the youngest, hottest, most luminous stars and by giant clouds of gas and dust within which such stars have recently formed.

spiral galaxy
: A
galaxy
characterized by a highly flattened disk of stars, gas, and dust, distinguished by
spiral arms
within the disk.

star
: A mass of gas held together by its
self-gravitation
, at the center of which
nuclear
fusion
reactions turn energy of mass into
kinetic energy
that heats the entire star, causing its surface to glow.

star cluster
: A group of stars born at the same time and place, capable of enduring as a group for billions of years because of the stars’ mutual gravitational attraction.

strong forces
: One of the four basic types of
forces
, always attractive, that act between nucleons (
protons
and
neutrons
) to bind them together in atomic nuclei, but only if they approach one another within distances comparable to 10
-13
cm.

sublimation
: The transition from the solid to the gaseous state, or from gas to solid, without a passage through the liquid state.

submillimeter
:
Electromagnetic radiation
with
frequencies
and
wavelengths
between those of
radio
and
infrared
.

supermassive black hole
: A
black hole
with more than a few hundred times the mass of the Sun.

supernova
(pl:
supernovae
): A
star
that explodes at the end of its
nuclear-fusing
lifetime, attaining such an enormous
luminosity
for a few weeks that it can almost equal the energy output of an entire
galaxy
. Supernovae produce and distribute
elements
heavier than
hydrogen
and
helium
throughout interstellar space.

telescope (gamma, X ray, ultraviolet, optical (visible), infrared, microwave, radio):
Astronomers have designed special telescopes and detectors for each part of the
spectrum
. Some parts of this spectrum do not reach Earth’s surface. To see the
gamma rays
,
X rays
,
ultraviolet
, and
infrared
that is emitted by many cosmic objects, these telescopes must be lifted into orbit above the absorbing layers of Earth’s atmosphere. The telescopes are of different designs but they do share three basic principles: (1) They collect
photons
. (2) They focus photons. And (3) they record the photons with some sort of detector.

temperature
: The measure of the average
kinetic energy
of random motion within a group of particles. On the
absolute
or
Kelvin temperature scale
, the temperature of a gas is directly proportional to the average kinetic energy of the particles in the gas.

thermal energy:
The energy contained in an object (solid, liquid, or gaseous) by virtue of its atomic or molecular vibrations. The average
kinetic energy
of these vibrations is the official definition of temperature.

thermonuclear:
Any process that pertains to the behavior of the atomic
nucleus
in the presence of high temperatures.

thermonuclear fusion
: Another name for
nuclear
fusion
, sometimes simply referred to as fusion.

thermophile
: An organism that thrives at high temperatures, close to the boiling point of water.

tides
: Bulges produced in a deformable object by the
gravitational force
from a nearby object, which arise from the fact that the nearby object exerts different amounts of force on different parts of the deformable object, since those parts have different distances from it.

UFOs (unidentified flying objects)
: Objects seen in the skies of Earth for which a natural explanation cannot be easily assigned, revealing either a profound ignorance within the scientific community or a profound ignorance within the observer.

ultraviolet radiation
:
Photons
with
frequencies
and
wavelengths
between those of
visible light
and
X rays
.

universe
: Usually taken to mean everything that exists, though in modern theories what we call the universe may prove to be only one part of a much larger “metaverse” or “multiverse.”

virus
: A complex of
nucleic acids
and
protein
molecules that can reproduce itself only within a “host” cell of another organism.

visible light
:
Photons
whose
frequencies
and
wavelengths
correspond to those detected by human eyes, intermediate between those of
infrared
and
ultraviolet
radiation.

Voyager
spacecraft
: The two NASA spacecraft, named
Voyager 1
and
Voyager 2
, that were launched from Earth in 1978 and passed by Jupiter and Saturn a few years later;
Voyager 2
went on to encounter Uranus in 1986 and Neptune in 1989.

wavelength
: The distance between successive wave crests or wave troughs; for
photons
, the distance that a photon travels while it oscillates once.

weak forces
: One of the four basic types of
forces
, acting only among elementary particles at distances of about 10
-13
cm or less, and responsible for the decay of certain elementary particles into other types. Recent investigations have shown that weak forces and
electromagnetic forces
are different aspects of a single
electro-weak force
.

white dwarf
: The core of a star that has fused
helium
into
carbon nuclei
, and therefore consists of carbon nuclei plus
electrons
, squeezed to a small diameter (about the size of Earth) and a high density (about 1 million times the density of water).

WMAP
(
Wilkinson Microwave Anisotropy Probe
)
satellite
: The satellite launched in 2001 to study the
cosmic background radiation
in much greater detail than the
COBE satellite
could achieve.

X rays
:
Photons
with
frequencies
greater than those of
ultraviolet
but less than those of
gamma rays
.