Astrophysics Flashcard

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The Universe
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A large collection of billions of galaxies
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Galaxy
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Large collection of billions of stars
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Our sun
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A star in the milky way galaxy
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Planets
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Orbit a star
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dwarf planet
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Small planets
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Moons
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orbit planets
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artificial satellite
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Orbit earth, built by humans
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Asteroids
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Lumps of rock and metal, found in asteroid belt, orbit sun
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Comets
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Lumps of ice and dust, highly elliptical orbits around sun
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Gravity
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Provides the force that creates orbits
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centripetal force
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A force that pulls object toward the centre of a circle, caused by gravity
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Objects travelling in a circle
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Constantly changing direction SO constantly accelerating SO resultant force
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instantaneous velocity
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Tangent to the orbital circle
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Gravitational field strength varies with
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Mass (larger mass = larger gfs) Distance (the closer you are to a star/planet, the stronger its gravitational field)
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The stronger the force
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The larger the instantaneous velocity is needed to balance it
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Comets orbit
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Elliptical and elongated Long orbital periods Tail points away from sun
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Comets are at their fastest
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When they are near the sun, the suns pull is stronger and they have most kinetic energy
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Comets are at their slowest
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When they are furthest from the sun where they have the most GPE
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Orbital speed
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2 x pi x orbital radius / time period
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geostationary satellites
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1 day orbital periods Orbit at same speed of earth rotating Satellite dishes point at these satellites Used for weather, communication, google earth
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Stellar evolution
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1. Nebula 2. Protostar 3. Main sequence star 4. Red/super red giant 5. White dwarf/supernova 6. Neutron star
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Nebula
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A large cloud of dust and gas in space
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Protostar
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Gravity pulls dust and gas together to form a protostar. As the temp rises, the particles gain energy and collide. The hydrogen nuclei undergo nuclear fusion to form helium nuclei. A star is born.
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main sequence star
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Thermal expansion and hydrogen are balanced
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Red/Super red giant
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Hydrogen in core begins to run out, the star is compresses and then gains energy and expands into a red giant/super red giant
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White dwarf
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Small stars become unstable, eject outer layers of dust and gas and leave behind core
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Supernova
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Big stars expand and contract several times and then explode into a supernova
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Neutron star
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The exploding supernova throws the layers of dust and gas into space, leaving behind a very dense core.
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Classifying stars (colours)
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The hotter the star, the more light of higher frequencies it will emit, blue is the hottest, red is the coolest
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absoloute magnitude
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How bright a star would be if it was a fixed distance from earth.
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Classifying stars (brightness)
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The lower the absolute magnitude, the brighter the star
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Hertzsprung-Russell diagram
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A graph of absolute magnitude against temperature
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Doppler effect
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A change in sound frequency caused by motion of the sound source, motion of the listener, or both. This is because the wavelengths bunch up
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Red shift
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Galaxies are moving away from one central point. The universe is expanding. The furthest galaxies are moving fastest The black lines are shifting towards the red end of spectrum
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Big bang
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Red shift – Universe is expanding, all matter started in one place? Cosmic Microwave Background Radiation – Detecting CMBR everywhere we observe, leftover energy from explosion?

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