Uploaded by Clare Clayton


In a relatively short period of time following the Big Bang, huge clouds of hydrogen and helium
gas began condensing under the pull of gravity to form the earliest stars. Millions, even billions
of those stars eventually collected into gigantic systems called galaxies, the building blocks of
the Universe. Astronomers estimate that the Universe today contains billions of galaxies and
roughly 100 sextillion (1 followed by 23 zeros) stars.
Our planet Earth is but one small member of an assemblage of worlds that surrounds one of
those stars in one of those galaxies. We call our little family of planets the solar system, which
formed about 4.6 billion years ago, and together, we journey through space and time. But we
are not unique. There are probably millions of similar cosmic neighbourhoods scattered
throughout just our galaxy alone.
Stars and solar systems are born within vast, tenuous clouds of gas and dust floating
through space known as nebulae. Astronomers believe that shock waves travel through
the nebulae from nearby stellar births, distant star explosions, or simply from passing
stars. The waves create denser pockets of gas within the clouds. These denser regions
contain more material and therefore exert a stronger gravitational pull, which attracts
still more gas and allows them to grow. Eventually, if the core of one of these growing
spheres of gas reaches a critical temperature and pressure, a process called thermo1
What were the earliest stars made of?
(1 mark)
Why can astronomers only estimate the number of galaxies?
(1 mark)
Why is it stated that we are not unique?
(1 mark)
What can a shock wave eventually result in?
(1 mark)
nuclear fusion begins and a new star is born
As our solar system formed, most of the material in our parent "solar nebula" fell in towards
the centre, eventually creating the Sun. The leftover debris flattened into a disk surrounding
the proto-Sun. Within that disk, small pockets of denser material began to develop, eventually
creating hundreds, if not thousands of planetesimals. Across eons of time, the planetesimals
either collided with one another to form larger single bodies or were pulled into the proto-Sun
by its growing gravitational field. Eventually, the system stabilized, leaving the solar system
that we know and inhabit today.
The Sun, marking the centre of our solar system, is a sphere of hot glowing hydrogen and
helium gas. Its incredible energy comes from thermonuclear fusion occurring deep within its
core. The temperature of the Sun's core may reach as high as 27 million 0 F (15 million 0 C),
while the pressure is nearly incalculable. Within such an environment, hydrogen atoms collide
with such force that their electrons are ripped away from the nuclei. In the process, helium is
formed and, as a by-product, enormous amounts of energy are released. In our Sun, the
released energy slowly migrates to the surface and is radiated into space. Fusion powers the
Sun, and has done so for nearly 5 billion years. It will continue to do so for another 5 billion
What was formed when the leftover debris finally stabilised?
(1 mark)
What type of reaction is responsible for Earth being heated?
(1 mark)
What is one unknown feature of the Sun?
(1 mark)
What is a by-product of the fusion of hydrogen nuclei?
(1 mark)
How far though its life cycle is our Sun? How do you know
(2 marks)
Orbiting around the Sun are the major planets, hundreds of moons, and uncountable
asteroids, comets, frozen Kuiper Belt Objects, and smaller rocky debris called meteoroids.
But despite this vast cadre, most of our solar system is empty space. If we imagine the
Sun reduced from its diameter of 870,000 miles (1 kilometres) to the size of a softball,
the Earth would appear as a tiny bead about 44 feet (13 metres) away. The Moon, our
nearest companion in space, would be a barely perceptible speck circling the Earth at a
distance of only 1 .4 inches (3.6 centimetres). Even Jupiter, the solar system's largest
planet, would span only 0.5 inches (1.3 centimetres). Distant Pluto would slowly creep
around the Sun at a distance of 1 , 750 feet (530 metres).
Some massive stars are hot enough to produce elements heavier than helium. When
stars reach the ends of their lives, they blow these heavier elements into space. The
thermonuclear fusion that takes place within the cores of stars has enriched a universe
that began with lightweight elements like hydrogen and helium. Our Sun is believed to be
a third generation star. It formed in a gas cloud containing heavier elements synthesized
by previous generations of stars. These elements now make up our rocky planet, the
gases we breathe,
the water in our oceans, and the chemicals within our bodies.
10 What objects (apart from the planets) are part of our Solar System?
1 1 Which objects make up most of the Solar System?
12 Which is the most distance planet in the Solar System? How do you
13 Name at least two elements which could be produced by massive stars?
14 Why is it believed that our Sun contains elements other than hydrogen
and helium?
15 The planet Saturn is approximately ten times as far from the Sun as Earth is.
What distance from the softball would this be on the model described