SP7 Astronomy Flashcards
what does gravitational field strength of a planet depend on?
mass of body + distance from centre to surface (radius)
what is an elliptical orbit? what is an example of a body that has this orbit?
squished oval shaped orbits - comets are elliptical
what are artificial satalites used for?
communication and to observe earth + space
What is true about the speed and direction ofcircular orbiting bodies?
the speed is constant but the direction is always changing - a principle of centripetal force
How does gravitational force differ from a satalite in low orbit to high orbit? why?
low has greater gravitional force than high - must be moving at a faster speed to stay in orbit
What happens when a satalite in low orbit slows down?
fall towards earth - can either gain enough speed to stay in a new, lower orbit, or it will go low enough to make contact with the atmosphere and air will slow it down till it eventually falls to earth
How is a star formed?
a nebula (cloud of dust + hydrogen) is formed by materials being pulled together by their own gravity. The cloud then becomes denser and the hydrogen hotter. More mass is attracted and the gravitaional pull of the cloud gets stronger + heats the materials even more. This new formation is called a protostar
What fusion reaction takes place in the centre of the protostar? what is released as a result?
hydrogen nuclei fuse to form helium - lots of energy is released like electromagnetic radiation
How does a protostar come into its main sequence after a fusion reaction?
the outward pressure of hot gases balances the compression due to gravity
what is the life cycle of stars like our sun?
nebula
protostar
main sequence
red giant
white dwarf
(black dwarf once cooled)
how long do stars like our sun remain stable for and what causes them to become unstable?
10 billion years - fused all hydrogen + helium together
what happens to turn a main sequence star into a red giant?
no more hydrogen to fuse - core is not hot enough to withstand gravity and collapses - outer layers expand
what happens to a red giant to form a white dwarf?
a futher pull of gravity and collapse to form white dwarf
what is the life cycle of massive starts
nebula
protostar
massive main sequence
red supergiant
supernova
neutron star or blackhole
what are massive stars?
stars with considerably more mass than the sun and are hotter and brighter
what turns a massive main star sequence into a red super giant?
faster fusing of hydroegn and helium
how is a supernova formed?
the end of the red supergiant life cycle - star rapidly collapses and explodes
how does a supernova form a black hole?
gravity pulls the remains of the star together if there is enough mass
how does a supernova form a neutron star?
if there is not enough mass, gravity pulls the star together to form a small dense star
what is the doppler effect?
when an emergancy vehicle moves away from you, the pitch of its siren gets lower
What is the science behind the doppler effect?
the pitch of sound depends on the frequency of the wave. sound waves behind a moving source become stretched making the wavelength longer which lowers the frequency so we hear a lower pitch. The opposite happens infront of a source
what is a red-shift?
when visable ligt of the star moves towards the red end of the spectrum
what can we infer from a red-shifted star?
the star is moving away from us
How can we tell how fast the star is moving relative to us?
the further the dark lines are shifted to the red end
what is the red-shift a measure of?
how far along the spectrum the lines have moved
what happens if a star is moving towards us
in terms of wave length and frequency?
wavelength of light becomes shorter and frequency increases so pattern of lines move to blue-end of spectrum
How did we come to the conclusion that the earth is exapnding?
Edwin Hubble found that the further away a galaxy is, the greater its red shift and hence the faster it is moving away from us
What is the premesis of the Big Bang Theory?
The whole universe and all the matter in it started out as a tiny point of concentrated energy and the universe expanded from this point - as universe expanded, gravity caused matter to clump together to form stars
What is the Steady State theory?
states the universe has always existed and is expanding - new matter is created within the universe as it expands
What does the Big Bang theory state in terms of raditation?
huge amounts of radiation were released at the begining of the universe - due to expansion, the wavelength of this radiation has increased and is now only detectable as microwave radiation.
what is the radiation called that the big bang theory predicted?
cosmic microwave background radiation - or CMB radiation
What theory does CMB radiation provide support for?
big bang
