Astro (11.5 - 11.7) - Sun, stars, galaxies, universe Flashcards
What is 1 light year
Distance travelled by light in 1 year.
9.5 10^12 km
What is interstellar matter
what is it mainly comprised of
Thinly spread gas and dust between stars
main gas is hydrogen
Motion of galaxy
Slowly rotating
Held together by gravitational attraction
What are galaxies made of
many billions of stars
Name the stages of the lifecycle of a star
Nebula (interstellar gas)
Protostar
Star
Red giants/Super red giants
White dwarf (red giant) or Supernova (super red giant) or black holes
Supernova –> neutron star
Why does a nebula become a protostar
interstellar cloud collapsing which forms a clump at the center which is then heated up
(why its heated up on another card)
Why is a protostar heating up
GPE of incoming material converted to thermal energy
When is a star stable formed from a protostar
When outward pressure from radiation of high temperature balance the inward pull of gravity.
What is a accretion disc
what does it become
Remaining gas and dust
Grains of materials are slowed by collisions and pulled into a clump by gravity
These become planets and moons
Why do the inner planets not have any gas
Sun’s radiation drove off all the gas. Thats why they are left small and rocky
Why are outer planets gas giants
Temp is cooler. Planets retain gas - become gas giants
Explain fusion in a star
Hydrogen molecules fuse together to form helium molecules. Give out a lot of energy while doing this
Why do nuclei not fuse readily
how to overcome this
They are electrically charged so they repel eachother.
Have to collide at extremely high speeds thats why u need sucha high temp - 15 mil Celsius
Explain the death of a star
Eventually, the star will run out of hydrogen for fusion. This will cause the core to collapse
What happens after the core collapses in the death of a star
most stars expand to form red giant
What happens to the red giant
forms a planetary nebula with a white dwarf star at its centre
What does the white dwarf use as fuel
what happens after
Uses helium to convert to carbon as fuel
after which itll cool and fade forever
what happens after a the super red giant phase of a massive star
Blow up in a gigantic nuclear explosion called a supernova forming a nebula containing hydrogen and new heavier elements, leaving behind a neutron star or a black hole at its centre
Why is a neutron star formed
The core becomes so compressed that electrons and protons form neutrons - forming a neutron star
What happens to the most massive of stars that form super red giants
Black holes
core cannot resist the pull of gravity and continues to collapse which creates a blackhole that nothing can escape from
What do scientists believe about blackholes in relation to galaxies
Theres a massive blackhole in the middle of each galaxy
What is the result of a fusion reaction in general
converts lighter elements to heavier ones
Reqiurements to make very heavy elements
why
Extreme conditions that create a supernova are needed.
Because to make elements heavier than iron, energy must be supplied for fusion and is not released
Why does the fact that super nova conditions are needed to make heavy elements relate to our solar system
how does this impact the sun in particular
The sun and inner planets contain very heavy elemetns
this suggests that the nebula in whhich the sun and inner planets was formed included ‘stardust’ from an earlier supernova.
thats why the sun is a second-generation star
What is the diameter of the milky way
100000 light-years
What is the doppler effect
As objects move away from an observer at high speeds, light waves from that object become stretched out.
What is red shift
Wavelengths of light emitted from far away objects are shifted towards red (longer wavelength)
Relation between red shift and distance
directly proportional
How does the light emitted from distant galaxies appear in comparison with
light emitted on the Earth
redshifted
What theory does redshift support
why?
Big bang theory
This means that galaxies are receding (in order to be red shifting)
Hence the unvierse is expanding
What does the big bang theory state
Universe began billions of years ago (13 to 15 bn) when a hot superatom called erupted into a burst of energy
2 evidence that support the big bang
Since galaxies are moving apart, they must have been together at one point
Radio telescopes pick up microwave radiation of a particular frequency coming from every direction in space which is the heavily redshifted remanats radiation of the big bang called CMBR
Full form of CMBR
Cosmic microwave backgrnd rad
Formula for Hubble Constant
V/D
v = speed at which galaxies are moving away from earth
d = distance of galaxies from earth
Value of hubbles constant
2.3 * 10^-18 per second
hubble constant and time eqn
Hubble constant = 1 / time
Age of universe eqn
age of universe = 1 / hubbles constant
which is roughly 13.8 seconds
what is redshift used to calculate
speed at which the galaxy is moving away from the earth
Why do we see the moon
Surface reflects sunlight
How do we see the full moon
Whole sunlit side of the moon faces us
Why can we only see part of the moon usually
usually only part of the sunlit side faces us, the rest is shadow
Stages of moon
new moon - full shadow
waxing crescent
first quarter
waxing gibbous
full moon
waning gibbous
third quarter
waning crescent
Amount of moon and shadow in
crescent
gibbous
crescent - 3/4th shadow, 1/4h moon
gibbous - 1/4th shadow, 3/4th moon
Which side is shadow in
‘waxing’
‘waning’
waxing - shadow left side
waning - shadow right side
describe shadow and moon in
new moon
full moon
quarters
new moon - all shadow no moon
full moon - all moon no shadow
quarters - half shadow half moon
first quarter - shadow left side
third quarter - shadow right side
thing to remember about moon
shadow goes from left to right as the month progresses
