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AQA Physics 3
Stars and the universe
21
Physics
11th Grade
03/10/2008

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Cards

Term

Nebula

Definition
A cloud of gas and dust
Term
Protostar
Definition

A very hot ball of gas formed when gravity pulls the gas and dust particles together.

Term
Stable star
Definition

When two Hydrogen atoms are fused together and form Helium because of the pressure.  This nuclear reaction is called fusion and results in the release of vast amounts of energy. 

The star stops shrinking because the gravitational force and pressure created by the fusion reactions are balanced.

Small stars burn fuel slower than big stars and have longer stable periods.

Term
Red giant
Definition
When a star runs out of Hydrogen fuel in its core it will start to contract again.  The remaining nuclear fuel in the skin of the star starts to undergo fusion and causes the star to expand.
Term

Supernova

Definition

Large dying stars literally explode when they run out of nuclear fuel.  Only the dense core of the star remains.

Term
Neutron star
Definition
The remaining core of a large star so dense that protons and electrons fuse together to make neutrons.
Term
Black hole
Definition
The remains of a really large star ay leave an incredibly dense core which has such a powerful gravitational field that even light cannot escape from it.
Term
Dwarf stars
Definition
Small stars which run out of nuclear fuel or were never big enough to undergo nuclear fusion gradually cool.
Term
What is the life cycle of a small star?
Definition
Nebula  → protostar → stable star → red giant → dwarf star
Term

What is the life cycle of a large star

Definition

Nebula → protostar → stable star → red giant → supernova → neutron star or black hole

Term
Define a star system
Definition
A star system is a star and the various objects which orbit that star like planets, natural satellites, comets and asteroids.
Term
Define a galaxy
Definition
A galaxy is a collection of stars which in astronomical terms are close together.  For example our star, the Sun and ourselves, are part of the milky way galaxy.  However the closest star to us in this galaxy is still 4 light years away!
Term
Define the universe
Definition
Everything that exists!  All the galaxies from our one universe.
Term
How does a protostar form?
Definition
An event like a supernova causes a region of gas to clump.  The gravitational forces betwwen the gas particles cause it to shrink further.  As this happens the as gets hotter and hotter.  A protostar has been formed.
Term
What is the difference between a protostar and a stable star?
Definition

The hot ball of gas called a protostar eventually becomes so hot and dense due to the gravitational forces that the hydrogen nuclei start to bond together and form helium nuclei.  This is called nuclear fusion, when this occurs it is no longer a protostar but now a stable star in the main part of its cycle.

Term
Why does a satble star stay the same size?
Definition
The gravitational force trying to shrink the satr are balanced by the outwards pressur ecaused by the nuclear fusion reactions.
Term
Why does a stable star become a red giant?
Definition
In the core of a star coming to the end of its stable stage it will run out of the hydrogen fuel required for nuclear fusion, the star will shrink but then the outer part of the star will start to undergo nuclear fusion causing the star to expand before gravitational forces overcome this and make the star shrink again.  This process is repeated a number of times.
Term
Why do small stars become brown dwarfs?
Definition

Eventually small stars simply run out of suitable fuel for nuclear fusion.  The stars gradually cools and changes colour eventually becoming a brown dwarf, a relatively cool star.  

(Some protostars are too small for nuclear fusion to even start and jump striaght to this stage -  not needed for syllabus or exam.)

Term
What are artificial satellites used for?
Definition
Telecommunications, weather and geographical observations, spying, global positioning and astronomical telescopes.
Term

Describe the orbits of a polar orbit satellite.

What are polar orbit satellites used for?

Definition

Polar satellites arbit across the north and south pole of the Earth.  Their orbit time can be changed depending on its speed.

Polar satellites are used for making weather and geographic observations as well as spying!

Term

Describe the orbit of a geostationary satellite.

How long does it take a geostationary satellite to complete one rotation?

What are geostationary satellites used for?

Definition

A geostationary satellite stays above one place on the Earth's surface.

Therefore it takes 24 hours for a geostationary to complete one rotation just like the Earth.

Geostationary satllites are primarily used for telecommunications and global positioning systems.

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