Section 8 - Astrophysics Flashcards
Universe
- large collection of billions of galaxies
Galaxy
large collection of stars
Sun
one of the billions of stars which form the Milky way Galaxy (about halfway long one of the spiral arms).
Gravity astrophysics
Gravity - force keeping stars together in a galaxy (galaxies rotate slightly)
universe made up of
Universe is mostly empty space. There is a great distance between stars, millions more than between neighbour plantes and an even greater distance between galaxies.
our galaxy
We are part of the Milky Way Galaxy:
Planets
Planets (large objects that orbit a star) Eight in our solar system (Mercury Venus Earth Mars Jupiter Saturn Uranus and Neptune) - my very easy method just speeds up nothin
Dwarf Planets
Dwarf Planets: (pluto) planet-like objects not large enough to be considered planets
Moons
Moons: Orbit planets with almost circular orbits. A natural satellite
Artificial satellites:
man-made objets orbiting earth in almost circular orbits
Asteroids
lumps of rock and metal that orbit sun, usually found in asteroid belt
Comets
Comets: lumps of ice and dust that orbit Sun. Orbits usually highly elliptical.
Centripetal Force -
acts towards the centre of a circle and causes the object to fall against whatever it is orbiting but as the object is already accelerating it just causes it to change direction. Object keeps accelerating towards what it is orbit ut the instantaneous velocity (right angle to acceleration) keeps it in a circle
Gravitational force
Gravitational force - the gravitational attraction of the Sun keeps the planets and comets in their orbits around it
satellites and orbit
Satellites kept in orbit by gravitational attraction of planet
Gravitational field strength what affects it
distance/ mass
depends on mass of body creating the field. The larger the mass the stronger the field (earth> moon so object weigh more on earth than moon)
Also varies with distance (closer you get to object the stronger the field)
Orbits of moons and planets
slightly elliptical
Comets orbit
Comets orbit Sun but have very elliptical orbit with sun at one focus (near an end of the orbit). They have orbital periods for much longer than earth as they travel from the outer edges of our solar system. A comet travels much faster when its near a star due to the increased pul of gravity that makes it speed up
Geostationary
Geostationary - Artificial earth satellites have an orbit period of exactly one day, useful in comunication because they are always over same part of planet
Calculate Orbit Speeds
Orbital speed = 2π x orbital radius / time
Nebula
Nebula - stars initially form a cloud of dust and gas
Protostar
Protostar - force of gravity pulls the dust and gas together to for a prostar. The temp rises as the star gets denser and more particles collide. When the temp is high enough hydrogen nuclei undergo nuclear fusion to form helium nuclei. This gives out huge amounts of energy which keep star core hot. Star is born
Main sequence stars-
Main sequence stars- star enters long stable period during which the outward pressure caused by thermal expansion (the energy produced by nuclear fusion tries to expand the star) balances force of gravity pulling everything inwards. This tyically lasts several billion years. The heavier the star the shorter time on the main sequence (sun is in middle of stable period).
Red giant/supergiant
Red giant/supergiant - eventually the hydrogen in the core begins to run out and the force of gravity is larger than pressure of thermal expansion. The star is compressed until it is dense and hot enough that the energy (and pressure) makes outer layers of star expand. It becomes a red giant or supergiant depending on its size. Red = because surface cools-
White dwarf
White dwarf a small to medium sized star (like sun) then becomes unstable and ejects its outer layer of dust and gas leaving behind a hot dense solid core called white dwarf
Supernova
Supernova - big stars start to glow brightly again as they undergo more fusion to make heavier elements . They expand and contract several times as the balance shifts between gravity and thermal expansion. eventually they explode in supernova
Neutron star/ black hole
Neutron star/ black hole - The exploding supernova throws 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 collapse and become a black hole - a super dense point in space not even light can escape
Colour of a star
Colour of a star depends of the amount of visible light it emits, all stars emit visible light but how much and its frequency depends on its surface temperature
Starts of similar colour will be of similar temperature
Hotter = more light of higher frequencies it will emit
Cool star - red, orange, yellow, white, blue - hottest - highest frequency light
