1001 Questions and Answers: World of Knowledge

1001 Questions and Answers: World of Knowledge

by V. Egan

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Barnes & Noble
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6 - 10 Years

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1001 Questions & Answers

Edited by Victoria Egan and Neil Champion

Barnes & Noble Books

Copyright © 1997 Andromeda Oxford Limited.
All rights reserved.
ISBN: 0760704104

Chapter One

What is the universe?

The universe contains everything that exists. It includes the Earth, the Sun and Moon, the other planets in our solar system, all the billions of stars, and all the space between them. With powerful telescopes and other scientific instruments, astronomers have found out a great deal of information about the universe and how it works. But there are still many unexplained mysteries.

Most astronomers believe that
the universe began about 15,000
million years ago with a gigantic
explosion, which they call the Big
Bang. Earth was formed 4,500
million years ago.

What was the Big Bang?

The Big Bang is the name given to the explosion that astronomers think started the universe. It was an unimaginably enormous explosion. All the material in the universe was in the form of energy, condensed into a tiny space. The temperature was probably about 20,000 million °F (10,000 million, °C). When the Big Bang happened, the energy began to spread out. The temperature fell and atoms started forming. Gradually the atoms clumped together and the first galaxies were made The outer galaxies of the universe are rushing away into space at great speed, showing that the universe is still expanding after the Big Bang.

Astronomers think that the
chances of other life existing are
very high. There is no reason to
think that our solar system is
particularly special, so there are
probably other Earth-like planets
orbiting some of the billions of
other stars like our own Sun.

Will the universe end?

There are different theories about what will happen to the universe. One theory, called the Steady State Theory, says that the universe will keep expanding. Another, the Oscillating Universe Theory, says that it will gradually shrink, and then there will be another Big Bang. This pattern will repeat itself about every 80,000 million years.

How far away are the stars?

It is tens of millions of millions of miles just to the Sun's neighbors, and most stars are thousands of times farther away than that. Stars at different distances from Earth seem to change position slightly as Earth moves in its orbit. This effect is called parallax. By measuring the amount a star seems to move, astronomers can work out how far away it is.

In 1543 Nicolaus Copernicus
put forward a theory that the Sun
was at the center of the universe,
and that the planets moved round
it. But the Catholic Church refused
to accept this, believing that
Earth was at the center of the
universe, and Copernicus's theory
was banned.

What is a "light-year"?

Distances in space are so huge that astronomers measure not in miles but in "light-years": the distance light travels in a year. Light travels at nearly 190,000 mph (300,000 kph), so a light year is about 5.9 million million mi. (9.5 million million km).

After our own Sun, the nearest
star to Earth is Proxima Centauri.
It is 4.2 light-years away, or about
25 million million mi. (40 million
million km). The Sun is a
mere 8 light-minutes from Earth.

We cannot see the edges of
the universe, so it is impossible to
tell if there is anything beyond it.
Scientists cannot even tell whether
the universe has edges as we think
of them.

Who were the first astronomers?

More than 4,000 years ago, Chinese astronomers were making accurate observations of the stars and planets. About the same time the Babylonians were recording the night sky. They believed that the stars revealed the ways of their gods. Many of the constellations are named after the gods of ancient times.

The first time a telescope was
used for astronomy was in 1609,
by the Italian scientist Galileo
Galilei. He discovered the four
large moons of Jupiter, and supported
Copernicus s theory that
the planets move round the Sun.

How big is the universe?

The universe is so vast that it is difficult to imagine. The most distant objects astronomers can see are quasars, which are up to 15,000 million light- years away. The light from these quasars left them soon after the Big Bang. There may be objects farther away than that, but we will never be able to see them because their light will never reach us.

Comets are bits of dust, ice
and gas that are zooming through
space. Astronomers think that
there is a huge cloud of icy lumps
beyond Pluto's orbit. When a
lump is pulled from the cloud, it
orbits around the Sun as a comet.
We see comets when their orbits
bring them close to the Sun.
Some come close every few years,
but others take thousands of years
to return.

What is a quasar?

In the 1960s, astronomers detected radio waves coming from immense distances in space. The waves were coming from objects that, through a telescope, looked like faint stars in our own galaxy. Studying the radio waves revealed that the objects were zooming away from us at almost the speed of light. These objects, known as quasars, are the most distant objects we can see, and are hundreds of times smaller and brighter than galaxies.

When a comet approaches the
Sun, its ice begins to melt. This
releases dust and gas, which make
a cloud around the comet. The
cloud is pushed into a tail by
streams of particles from the Sun
called the solar wind. The tail
always points away from the Sun.

How can black holes be detected?

As a black hole and its companion star rotate around each other, the gas from the star is funneled by the force of gravity into a disc around the black hole. The gas molecules in the disc swirl around the black hole so fast that they heat up and emit X-rays. These X-rays can be detected from Earth.

What is a black hole?

When a giant star comes to the
end of its life, it grows into a huge
ball and blows itself apart in an
explosion called a supernova. The
material left collapses in on itself
until it becomes a tiny point in
space. The gravity in the area
around the point is so strong that
not even light can escape, which
is why it is called a "black hole."

The northern lights, or Aurora
Borealis, is a greenish-blue glow
of light that makes slowly changing
patterns in the sky near the
North Pole. It happens when electrically
charged particles from the
Sun (the solar wind) are drawn to
Earth's magnetic poles. When
they reach Earth's upper atmosphere
they become trapped, bombarding
the atoms there and
emitting radiation.

What made the craters on the Moon?

A crater is made when a meteorite crashes into the surface of a planet or moon. Most of the craters on the Moon were made soon after it was formed, as it was hit by thousands of meteorites. The craters are still there because the Moon has no atmosphere to erode them.

What is a pulsar?

When a large star comes to the
end of its life, it can collapse in on
itself to form an extremely dense,
spinning star called a neutron star.
Because it sends out a beam of
radio waves as it spins, a neutron
star is also called a pulsating star,
or pulsar.

What did astronauts
find on the moon?

For thousands of years, people
had no idea what the Moon was
made of. This mystery was only
solved when astronauts brought
back many samples of lunar rock
and dusty soil. The samples
showed that the Moon's surface
contains a volcanic rock similar
to basalt.

Why do stars seem to
move across the sky?

If you take a quick glance at
the sky, the stars seem to be fixed
in place. But look again a few
minutes later and they will appear
to have moved slightly. The
movement is caused by Earth
spinning in space.

Why do some planets have rings?

The planets Jupiter, Saturn, Uranus, and Neptune have rings around their equators made from chunks of ice, dust, or boulders. These particles were either left over when the planets were formed, or they may be the remains of broken-up moons.

As fragments of rock from
space, called meteors, hurtle into
Earth's atmosphere, they burn up.
This is visible as a streak of light,
making them appear like stars
shooting across the sky.

Do all planets have an atmosphere?

Each of the planets is surrounded by a blanket of gases called an atmosphere. Earth's atmosphere is made up mostly of oxygen and nitrogen, and protects us from the Sun's harmful rays. The other planets' atmospheres consist of different gases.

What is a galaxy?

A galaxy is a huge cluster of
stars held together by gravity.
There are millions of galaxies in
the universe, and even the smallest
contain millions of stars.
Between the galaxies are vast, starless
spaces. Light from the galaxies
takes millions of years to reach us.

What shapes are the galaxies?

A spiral galaxy, like the Milky Way, has a central lump with several "arms" spinning out from the center. Elliptical galaxies are shaped like flattened spheres. Irregular galaxies have no particular shape at all.

Where did the galaxies come from?

Astronomers think that the galaxies in the universe were formed after the Big Bang, when space was full of energy. The energy gradually turned into atoms. Over millions of years these atoms drifted together under gravity into clouds of gas, and formed into galaxies containing stars and planets.

Can other galaxies be
seen in the sky?

If you have very good eyesight,
you can see three other galaxies.
They look like tiny, fuzzy patches
of light. You cannot see individual
stars in these galaxies — even
with a powerful telescope — because
they are so far away.

What is a nebula?

A nebula is a gigantic cloud of dust and gas, which can be hundreds of light-years across. Some nebulae look dark because they block out light from stars behind them. Other nebulae are bright because they reflect light from stars or because their gas gives off light. Some nebulae gradually clump together and form new galaxies.

What is the Milky Way?

The Milky Way is the name of
the galaxy to which our solar
system belongs. It is also the name
given to the bright band of light
from millions of stars that you
can see stretching across the sky
on dark, clear nights.

The distance from one end of
the Milky Way to the other is
about 100,000 light-years, and it
is about 20,000 light-years deep.
It contains about 100,000 million
stars. Our Sun is about two thirds
of the way out from the center on
one of the spiral arms, called the
Orion arm.

How many galaxies are there?

Astronomers estimate that there are about 100,000 million galaxies in the universe, gathered together in clusters. Some clusters contain thousands of galaxies. Others contain less than a hundred. Our own cluster, called the local group, may contain about 30 galaxies. Clusters of galaxies also group together in superclusters, which are hundreds of millions of light-years across.

What does a radio telescope do?

Objects in space give off a variety of electromagnetic waves, such as light waves, radio waves and X-rays. A radio telescope detects radio waves coming from space. It can also detect quasars and other objects that cannot be seen with an optical telescope (one that collects light waves). A radio telescope has a large dish aerial that collects radio waves and bounces them into a receiver, which converts them into electrical signals.

What lies in between
the galaxies?

In between the billions of
galaxies in the universe are huge
expanses of empty space. But
space is not completely empty.
Every cubic yard contains about
half a million atoms (a hundred
million million million times
fewer than a cubic yard of air).

Why are radio maps useful?

A radio map can give a more accurate picture of a galaxy than the optical image received by a telescope. It is built up from radio waves emitted by the galaxy. These may come from a wider area than can be seen with a telescope, or their source may be a small area at the center of the galaxy.

The nearest galaxy to our own is
an irregular galaxy called the
Large Megallanic Cloud (LMC
for short).

In the 1920s, the astronomer
Edwin Hubble proved that there
were other visible galaxies in the
night sky, outside our own galaxy
and much farther away.

What is a star?

A star is a huge ball of gas that gives off vast amounts of light and heat. The Sun is our local star. It is about 900,000 mi. (1.4 million km) across. More than a million Earths could fit inside it. Being made of gas, it has no solid surface. Energy is made in the Sun's core, where the temperature is about 60 million °F (15 million °C); it travels to the surface to emerge as light and heat. The Sun is close enough for us to see it as a disk in the sky, and it provides all the energy needed to keep life going on Earth. Because they are so distant, other stars appear as points of light.

Astronomers estimate that
our galaxy (star system) — the
Milky Way — contains 100,000
million stars. There may be
100,000 million galaxies in the
universe. That is a total of 10,000
million million million stars!

What are sunspots?

Just like Earth, the Sun creates magnetic fields inside and around itself. These sometimes stop the heat from the center of the Sun reaching the surface. In places where this happens, cooler, dark areas, called sunspots, appear. Some last just a few days. Others are as big as planets and last for months. Solar flares are another surface feature of the Sun. They are huge eruptions of flame.

How bright a star appears to be
depends not only on how bright
it really is, but also on how far
away it is. A dim star that is close
to us can appear brighter than a
more distant, brighter star.

What makes the sun shine?

The Sun shines because it gives out light and heat, which are forms of energy. The energy is made by nuclear reactions in the Sun's core. Extreme temperatures and pressure at the core make hydrogen atoms join together to form helium atoms. This process is called nuclear fusion, and it creates huge amounts of energy. It can take a million years for the energy produced in the core to reach the surface.

The Sun is a type of star called a
"yellow dwarf," because it is small
compared with other types and
gives off yellow light. Some stars
are a hundred times bigger. Others
are as small as the Moon.

What is a constellation?

A constellation is a group of stars that forms a pattern. Some of the 88 constellations are easier to spot than others. Different constellations are visible from different parts of Earth. Some are visible only from places in the Northern Hemisphere; others can be seen only from the Southern Hemisphere. As Earth orbits the Sun, different constellations become visible as Earth's dark side faces different parts of the night sky.


Excerpted from 1001 Questions & Answers by Victoria Egan and Neil Champion. Copyright © 1997 by Andromeda Oxford Limited. Excerpted by permission. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.

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