HOW MANY DIFFERENT GALAXIES ARE THERE?
The Universe contains a hundred billion galaxies,
and there are four main types. Spiral galaxies have
a central bulge of stars, with other stars in a pattern
of curved arms. Barred spirals have arms coming
from a bar through their centre. Ellipticals are
round or oval, with no spiral arms. An irregular is
a galaxy with no special shape. The largest galaxies in a
. GALAXY CLUSTER are mostly spirals and ellipticals.
HOW DOES THE MILKY WAY LOOK FROM EARTH?
Earth sits out near the end of one of the Milky Way’s
spiral arms, so we have an excellent view of the rest
of our galaxy. From Earth, the Milky Way appears as
a pale band of light across the night sky. It is a flat
spiral, and we see it from the side, so it seems long
and thin to us. The dark rifts in the Milky Way are
huge dust clouds that hide the stars behind them.A galaxy is a vast collection of stars, gas,
and dust spinning in space and held together
by gravity. All the stars in the sky belong
to our own galaxy, the. MILKY WAY.
WHAT ARE ACTIVE GALAXIES?
A few galaxies, called active galaxies, create huge
amounts of energy. At their centre, they have a
massive black hole that generates a trillion times
more power than our Sun, and spits out jets of
electrically charged particles. Quasars and radio
galaxies are both types of active galaxy.
WHAT IS THE LOCAL GROUP?
Our Milky Way Galaxy belongs to a galaxy cluster called the Local
Group. It contains about 30 galaxies, including our near neighbours, the
Andromeda Galaxy and the Magellanic Clouds, which we can see with
the naked eye. Most of the galaxies are ellipticals or irregulars.
Our home in the Universe is the Milky Way
Galaxy. It is a barred spiral galaxy that
contains our Sun and 200 billion other
stars, among vast clouds of dust and gas.
It is about 100,000 light years across.A galaxy cluster is a large number of
galaxies that are grouped together in space.
The Virgo Cluster, for example, contains
at least 2,000 galaxies.
WHEN GALAXIES COLLIDE 3
Galaxies sometimes collide
with one another. The larger
Cartwheel Galaxy shown here was
once an ordinary spiral galaxy.
But some 300 million years ago, a
smaller galaxy passed through it,
breaking up its spiral arms and
producing a ring of new stars.GALAXIES
Galaxies
MAPPING THE UNIVERSE 3
A supercluster is a group of
clusters. This computer-generated
map shows the superclusters of
galaxies that make up our part of
the Universe. They are separated
by vast empty spaces called voids.COMA CLUSTER 3
A view of the Coma Cluster, which contains up
to 3,000 galaxies. It lies about 300 million light
years away, in the constellation Coma Berenices.
Most of the objects in this picture are galaxies.4 ABOVE THE SPIRAL
Viewed from above, the Milky Way Galaxy would look like a slowly
spinning Catherine-wheel firework, with spectacular spiral arms.GALAXY CLUSTERS
MILKY WAY
GALAXY TYPES
Early last century, the
astronomer Edwin Hubble
put galaxies into groups
according to their shape.1 IRREGULAR GALAXY1 BARRED SPIRAL GALAXYSPIRAL GALAXY 11 ELLIPTICAL GALAXYFIND OUT MORE. Earth 16 • Solar System 14 • Space 10 • Stars 24–25 • Sun 15
galaxies