3. Stars
A star is a massive, luminous sphere of plasma held
together by gravity.
Ex: the sun is a star
4. Life Cycles of Stars
Every star has a life cycle: a beginning, a middle
and an end. At the beginning, a star forms from
a massive cloud of gases and dust called a
nebula (gases include hydrogen and helium).
5. Life Cycles of Stars
The gravitational forces begin to pull the gas and
dust particles close together, creating clumps. The
clumps become more massive and gravity becomes
even stronger. Over time, a dense region forms,
called the protostar.
6. Life Cycles of Stars
Gravity causes the core of the protostar to
become very tightly packed and the pressure
causes nuclear fusion to begin. Hydrogen atoms
in the core fuse to make helium atoms and as a
consequence, produce tremendous amounts of
energy.
7. Life Cycles of Stars
Billions of years after forming, the star begins
to burn out.
8. Life Cycles of Stars: Stars like the Sun
For about 10 billion years, a star’s available hydrogen
will have been converted to helium. With less
hydrogen to burn, the core begins to contract and
gets hotter, while the outer layers of the star expand
and then cool. The star evolves into a red giant.
10. Life Cycles of Stars: Stars like the Sun
Our sun will become a red giant in 5 billion years.
The outer layers of the star expand sharply, pouring
solar matter into space. This leaves a small, dim hot
core behind – a white dwarf.
11. Life Cycles of Stars: Stars like the Sun
As the sun’s mass
reduces, the planets
will not be attracted to
the Sun as strongly as
at present and their
orbits around the Sun
will shift further
outwards. The Earth
will gradually move to
where the planet Mars
orbits today.
15. More massive stars
Stars that are more
massive than our Sun (i.e.
10 times more larger) will
become a red supergiant.
Once fusion stops, the
supergiant will have its
contents collapse on its
self under its own gravity.
The outer layers of the
star explode outwards –
known as a supernova.
16. Supernova
All the atoms we are
made from came
originally from these
giant supernova
explosions.
17. If a star’s initial mass was:
• between 10 and 30 solar masses a neutron
star is formed – an extremely dense star
composed of tightly packed neutrons.
• greater than 30 solar masses black hole is
formed – a quantity of matter so dense and
gravity so strong that not even light can
escape.
26. Asterisms and Constellations
Asterisms: smaller
groups of stars that
form patterns within
a constellation
i.e. the Big Dipper
(an asterism) is part
of the constellation
Ursa Major
32. Constellations
The constellations you can see depend on your
latitude as well as the time of night and time of year
The images below show the North Sky viewed in the:
Spring vs Winter
