of David Darling > Children's Encyclopedia
of Science > Could You Ever Build a Time Machine? > Glossary
COULD YOU EVER BUILD
A TIME MACHINE?
a book in the
Could You Ever? series by David Darling
Very small, single-celled plants that exist in large numbers almost everywhere
A thousand million, written as 1,000,000,000.
Two stars that are close together and circle around one another; according
to some estimates, roughly half of all stars are members of binary systems.
A region of space in which the pull of gravity is so strong that nothing,
not even light, can escape. A black hole may form from the squashed remains
of a very heavy star after the outer parts of the star have been blown away
in a supernova explosion.
The smallest living unit making up an animal or plant. Cells are usually
too small to be seen without the help of a microscope. They come in many
forms and serve many different purposes. Examples include red blood cells,
bone cells, and brain cells.
In a star, the extremely hot region in the middle where the star produces
its light and heat.
A French expression meaning "already seen;" deja vu is the name for the
strange feeling people have that what is happening has happened once before.
A very large collection of between a few billion and a few hundred billion
stars. The galaxy in which we live, the Milky Way Galaxy, is a spiral in
shape, contains more than 200 billion stars, and measures more than 100,000
A force exerted by any object that has mass. The Earth's gravity is the
force that prevents the atmosphere, and people, from floating away into
A unit used by astronomers to measure distances in the Universe. It is the
distance that light, traveling at 186,282 miles per second, covers in a
year. One light-year equals 5.85 trillion miles.
Mass can be thought of in two ways. It is a measure of the amount of matter
in an object. Mass is also a measure of how hard it is to make an object
move or make it move in a different way.
The supposed ability of some people to be able to know what is going to
happen or to sense clearly certain events in the future. It can take various
forms, from "fortune telling" to dreaming about disasters before they occur.
Similar to precognition, but more of a vague feeling about the future than
certain knowledge. There is still not enough evidence to show whether premonition
and precognition are real or not. Most scientists assume they are not.
There are two types of supernova. The one discussed in this book involves
the explosion of an old, very massive type of star known as a supergiant.
One of the possible results of a supernova is a black hole.
A tiny, water-dwelling creature that can survive when most of the water
in its body is lost. This allows the tardigrade to live through periods
of drought and then become active again when water returns to its surroundings.
A million million; written as 1,000,000,000,000.
"Unidentified Flying Object." A UFO is any object seen in the sky for which
there is no immediate explanation. Although many UFOs do turn out simply
to be airplanes, bright stars or planets, or unusual clouds, a small number
The type of object that an average-sized star like the Sun becomes after
it stops producing light and heat in its core. Most white dwarfs are from
one to three times the size of the Earth.
In theory, possibly the other end of a black hole. Instead of being like
a whirlpool that sucks everything into it that comes too close, a white
hole would look like a geyser in space from which matter and light would
In theory, a sort of tunnel that connects a black hole to some other region
of space and time. Wormholes may or may not exist. If they do, they might
be like subways connecting different parts of our own universe or even other
Rays that are similar to ordinary light but which carry much more energy.
X-rays may be produced in a variety of ways in space. One of these is by
gas heated to millions of degrees.