Stars initially form from a cloud of dust and gas called a nebula.
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What is the life cycle of a star? (Step 2)
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
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helium nuclei. This gives out huge amounts of energy, which keeps the core of the star hot. A star is born.
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What is the life cycle of a star? (Step 3)
Star enters a long stable period where outward pressure caused by nuclear fusion that tries to expand star balances force of gravity pulling everything inwards. This period is called a main sequence star and it typically lasts several billion years.
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What is the life cycle of a star? (Step 4)
Eventually hydrogen begins to run out. The star then swells into a red giant (smaller star) or a red super giant (larger star). It becomes red because the surface cools. Fusion of helium occurs. Heavier elements are created in the core of the star.
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What is the life cycle of a star? (Step 5)
A small-to-medium-sized 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.
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What is the life cycle of a star? (Step 6)
As a white dward cools down, it emits less and less energy. When it no longer emits a significant amount, it is called a black dwarf.
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What is the life cycle of a star? (Step 7)
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 nuclear reactions. Eventually they'll explode in a supernova, forming elements heavier than iron
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and ejecting them into the universe to form new planets and stars. Stars and their life cycles produce and distribute all naturally occurring elements.
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What is the life cycle of a star? (Step 8)
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 tht not even light can escape from.
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What are planets?
Large objects that orbit a star. 8 in our solar system. They have to be large enough to have 'cleared their neighbourhoods'. This means that their gravity is strong enough to have pulled in any nearby objects apart from their natural satellites.
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What are the 8 planets?
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
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What are dwarf planets?
Planet-like objects that orbit stars, but don't meet all of the rules for being a planet.
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What are moons?
These orbit planets. They're a type of natural satellite.
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What are artificial satellites?
They are satellites that humans have built. They generally orbit the Earth.
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What does gravity provide?
It provides the force that creates orbits.
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What does the size of the orbit depend on?
The object's speed.
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The closer you get to a star or planet.....
The stronger the gravitational force is.
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The stronger the force.....
The faster the orbitting object needs to travel to remain in orbit.
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For an object in a stable orbit...
If the speed of the object changes, the size (radius) of its orbit must do so too. Faster moving objects will move in a stable orbit with a smaler radius than slower moving ones.
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What is the evidence for the universe geting bigger? (2)
When we look at light from most distant galaxies, we find that the wavelength has increased. The wavelengths are all longer than they should be - they're shifted towards the red end of the spectrum. This is called red-shift. This suggests the source
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of the light is moving away from us. Measurements of the red-shift indicate that these distant galaxies are moving away from us very quickly-and it's the same result whichever direction you look in. More distant galaxies have greater red-shifts than
nearer ones. The inescapable conclusion appears to be that the whole universe is expanding.
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What does this evidence suggest?
The Universe started with the Big Bang.
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What is the Big Bang theory?
Initially, all the matter in the universe occupied a very small space. This tiny space was very dense and so was very hot. Then it 'exploded' - space started expanding, and the expansion is still going on.
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Other cards in this set
Card 2
Front
What is the life cycle of a star? (Step 2)
Back
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
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