Space
The Solar System:
• A planet is a large body which orbits the sun.
• The planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
• A moon is a natural satellite that orbits a planet.
• Artificial satellites are satellites that humans have built, they generally orbit the Earth.
• A dwarf planet is large enough for its own gravity to have shaped it as roughly spherical. There are five
dwarf planets – Ceres, Pluto, Haumea, Makemake and Eris.
• Gravity causes planets to orbit the Sun. Gravity causes the moon and artificial satellites to orbit the
Earth. Gravity causes stars to orbit around the centre of their galaxies.
Life Cycle of Stars:
• Stars initially form from a cloud of dust and gas called a nebula.
• The force of gravity pulls the dust and gas together to form a protostar. The temperature rises as the
star gets denser and more particles collide with each other. When the temperature gets high enough,
hydrogen nuclei undergo nuclear fusion to form helium nuclei. This gives out huge amounts of energy,
which keeps the core of the star hot.
• The star enters a long stable period where the outward pressure caused by nuclear fusion that tries to
expand the star balances the force of gravity pulling everything inwards. In this stable period, it’s called
a main sequence star and it typically lasts several billion years.
• Eventually the hydrogen begins to run out. The star then swells into a red giant if it is a small star or a
red super giant if it is a larger star. It becomes red because the surface cools. Fusion of helium occur.
Heavier elements up to iron are created in the centre of the star.
• A small star like the sun then becomes unstable and ejects its outer layer of dust and gas. This leaves
behind a hot, dense solid core – a white dwarf. As a white dwarf cools down, it emits less and less
energy. When it no longer emits a significant amount of energy it is called a black dwarf.
• Big stars, start to glow brightly again as they undergo more fusion and expand and contract several
times, forming elements as heavy as iron in various in various nuclear reactions. Eventually they’ll
explode into a supernova, forming elements heavier than iron and ejecting them into the universe to
form new planets and stars. Stars and their life cycles produce and distribute all naturally occurring
elements.
• The exploding supernova throws the outer layers of dust and gas into space, leaving a very dense core
called a neutron star. If the star is massive enough, it will become a black hole – a super dense point in
space that not even light can escape from.
Orbits:
• Although planets and moons move in elliptical orbits, many of the orbits are very nearly circular.
• In a circular orbit:
o A planets velocity changes, but its speed remains constant.
o The planet accelerates towards the Sun which causes it to change direction.
o Gravity provides the force to accelerate the planet.
• The closer you get to a star or planet, the stronger the gravitational force is. The stronger the force,
the faster the orbiting object needs to travel to remain in orbit. For an object in a stable orbit, if the
The Solar System:
• A planet is a large body which orbits the sun.
• The planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
• A moon is a natural satellite that orbits a planet.
• Artificial satellites are satellites that humans have built, they generally orbit the Earth.
• A dwarf planet is large enough for its own gravity to have shaped it as roughly spherical. There are five
dwarf planets – Ceres, Pluto, Haumea, Makemake and Eris.
• Gravity causes planets to orbit the Sun. Gravity causes the moon and artificial satellites to orbit the
Earth. Gravity causes stars to orbit around the centre of their galaxies.
Life Cycle of Stars:
• Stars initially form from a cloud of dust and gas called a nebula.
• The force of gravity pulls the dust and gas together to form a protostar. The temperature rises as the
star gets denser and more particles collide with each other. When the temperature gets high enough,
hydrogen nuclei undergo nuclear fusion to form helium nuclei. This gives out huge amounts of energy,
which keeps the core of the star hot.
• The star enters a long stable period where the outward pressure caused by nuclear fusion that tries to
expand the star balances the force of gravity pulling everything inwards. In this stable period, it’s called
a main sequence star and it typically lasts several billion years.
• Eventually the hydrogen begins to run out. The star then swells into a red giant if it is a small star or a
red super giant if it is a larger star. It becomes red because the surface cools. Fusion of helium occur.
Heavier elements up to iron are created in the centre of the star.
• A small star like the sun then becomes unstable and ejects its outer layer of dust and gas. This leaves
behind a hot, dense solid core – a white dwarf. As a white dwarf cools down, it emits less and less
energy. When it no longer emits a significant amount of energy it is called a black dwarf.
• Big stars, start to glow brightly again as they undergo more fusion and expand and contract several
times, forming elements as heavy as iron in various in various nuclear reactions. Eventually they’ll
explode into a supernova, forming elements heavier than iron and ejecting them into the universe to
form new planets and stars. Stars and their life cycles produce and distribute all naturally occurring
elements.
• The exploding supernova throws the outer layers of dust and gas into space, leaving a very dense core
called a neutron star. If the star is massive enough, it will become a black hole – a super dense point in
space that not even light can escape from.
Orbits:
• Although planets and moons move in elliptical orbits, many of the orbits are very nearly circular.
• In a circular orbit:
o A planets velocity changes, but its speed remains constant.
o The planet accelerates towards the Sun which causes it to change direction.
o Gravity provides the force to accelerate the planet.
• The closer you get to a star or planet, the stronger the gravitational force is. The stronger the force,
the faster the orbiting object needs to travel to remain in orbit. For an object in a stable orbit, if the
