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Galaxies
Galaxies consist of
billions of stars bound
together by the force of
gravity.
There are thought to be
at least 200 billion
galaxies in our Universe
each containing on
average 2 billion stars.
The Andromeda Galaxy
The Sun’s position in the Milky Way
Types of galaxy
Barred-Spiral – NGC 1300
Our galaxy is this type
Spiral – The Whirlpool Galaxy
Elliptical – M32
Irregular – The Small
Magellanic Cloud
Choose appropriate words to fill in the gaps below:
Universe
The ___________
is made up of billions of galaxies which
billions
consist of __________
of stars bound to each other by the force
of ___________.
gravity
galaxy
Sun is
The name of our _________
is The Milky Way. The ______
located towards the outer edge of our galaxy.
spiral
The are different types of galaxy; ________,
barred-spiral,
barred-spiral
elliptical and irregular. The Milky Way is a ____________
Andromeda
galaxy. The _____________
Galaxy is the nearest spiral galaxy
to the Milky Way.
WORD SELECTION:
Andromeda galaxy spiral
Sun Universe
gravity
barred-spiral
billions
Stars
A star is a massive,
luminous ball of gas that is
held together by gravity.
The Sun is a typical star that
consists of about 75%
Hydrogen, 24% Helium and
1% other elements such as
carbon and oxygen.
There are about 2 billion
stars in our galaxy.
The Pleiades Star Cluster
The birth of the Sun
Nebula
Stars usually form
inside a nebula.
This is a cloud of
mostly hydrogen
along with smaller
amounts of other
elements ‘dust’.
Many young stars are found
inside the Orion nebula
The life history of a star
Notes questions from pages 268 & 269
1.
2.
3.
4.
5.
6.
7.
Copy Figure 2 on page 269.
Outline the life history of a star like our Sun. Your account should
include what is meant by (a) protostar, (b) red-giant, and (c) white
dwarf.
Explain the additional stages undergone by the most massive
stars. Your account should include what is meant by (a)
supernova, (b) neutron star, and (c) black hole.
(a) How does a star produce energy? (b) Explain why the Sun is
neither expanding or contracting at the present time.
Copy and answer questions (a), (b), (c) and (d) on pages 268 and
269.
Copy the ‘Key points’ table on page 269.
Answer the summary questions on page 269.
The life history of a star
ANSWERS
In text questions:
(a) The potential energy of
gas and dust decreases
when it gathers and is
transformed into heat
energy.
(b) The outward pressure
of radiation from its
core stops it collapsing.
(c) Gravity.
(d) Gravity.
Summary questions:
1. (a) B, A, C, D.
(b) (i) A
(ii) It will fade out and go
cold.
2. (a) (i) Expand, collapse.
(i) Explode, collapse.
(b) (i) The neutron star
must have sufficient
mass.
(ii) The gravitational field
is so strong that nothing
can escape from it.
The formation of elements
Hydrogen and helium
Hydrogen and some helium
was formed at the time of
the Big Bang.
Helium is also formed by
nuclear fusion in main
sequence stars like the
Sun.
Lighter elements
Elements such as carbon,
oxygen and silicon are
formed by nuclear fusion
in red-giant stars.
The heaviest element
formed in red-giants is iron.
The internal ‘onion’ structure
of a red supergiant star
Heavier elements
All elements heavier than
iron are thought to have
been formed during
supernovae explosions.
The fact that such elements
exist on Earth is evidence
that our Sun and the entire
solar system has been
formed out of the supernova
explosion of an earlier star.
Elements such as copper, gold
and uranium were formed in
supernovae explosions
Choose appropriate words to fill in the gaps below:
The lightest and most common element in the Universe is
hydrogen
helium
___________.
Hydrogen and some __________
were formed
from the Big Bang.
fusion
Most elements have been formed by nuclear _________
in the
lighter
cores of stars. Helium and the __________
elements such as
carbon
_________
are formed by stars like the Sun.
iron
Elements up to ______
are formed in the core of red
supergiant stars. The heaviest elements are formed in
supernovae explosions.
___________
WORD SELECTION:
carbon
hydrogen
fusion
helium
lighter
iron
supernovae
The light year
A light year is the distance travelled by light in
one year.
Light travels at 300 000 000 metres per second
= 300 000 kilometres per second
= 18 million kilometres per minute
= 1.08 billion km per hour
= 26 billion km per day
= 9.5 trillion km per year!