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Physics > Astro (11.5 - 11.7) - Sun, stars, galaxies, universe > Flashcards

Astro (11.5 - 11.7) - Sun, stars, galaxies, universe Flashcards

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1
Q

What is 1 light year

A

Distance travelled by light in 1 year.

9.5 10^12 km

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2
Q

What is interstellar matter

what is it mainly comprised of

A

Thinly spread gas and dust between stars

main gas is hydrogen

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3
Q

Motion of galaxy

A

Slowly rotating
Held together by gravitational attraction

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4
Q

What are galaxies made of

A

many billions of stars

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5
Q

Name the stages of the lifecycle of a star

A

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

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6
Q

Why does a nebula become a protostar

A

interstellar cloud collapsing which forms a clump at the center which is then heated up

(why its heated up on another card)

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7
Q

Why is a protostar heating up

A

GPE of incoming material converted to thermal energy

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8
Q

When is a star stable formed from a protostar

A

When outward pressure from radiation of high temperature balance the inward pull of gravity.

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9
Q

What is a accretion disc

what does it become

A

Remaining gas and dust

Grains of materials are slowed by collisions and pulled into a clump by gravity

These become planets and moons

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10
Q

Why do the inner planets not have any gas

A

Sun’s radiation drove off all the gas. Thats why they are left small and rocky

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11
Q

Why are outer planets gas giants

A

Temp is cooler. Planets retain gas - become gas giants

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12
Q

Explain fusion in a star

A

Hydrogen molecules fuse together to form helium molecules. Give out a lot of energy while doing this

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13
Q

Why do nuclei not fuse readily
how to overcome this

A

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

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14
Q

Explain the death of a star

A

Eventually, the star will run out of hydrogen for fusion. This will cause the core to collapse

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15
Q

What happens after the core collapses in the death of a star

A

most stars expand to form red giant

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16
Q

What happens to the red giant

A

forms a planetary nebula with a white dwarf star at its centre

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17
Q

What does the white dwarf use as fuel

what happens after

A

Uses helium to convert to carbon as fuel

after which itll cool and fade forever

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18
Q

what happens after a the super red giant phase of a massive star

A

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

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19
Q

Why is a neutron star formed

A

The core becomes so compressed that electrons and protons form neutrons - forming a neutron star

20
Q

What happens to the most massive of stars that form super red giants

A

Black holes

core cannot resist the pull of gravity and continues to collapse which creates a blackhole that nothing can escape from

21
Q

What do scientists believe about blackholes in relation to galaxies

A

Theres a massive blackhole in the middle of each galaxy

22
Q

What is the result of a fusion reaction in general

A

converts lighter elements to heavier ones

23
Q

Reqiurements to make very heavy elements

why

A

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

24
Q

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

A

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

25
Q

What is the diameter of the milky way

A

100000 light-years

26
Q

What is the doppler effect

A

As objects move away from an observer at high speeds, light waves from that object become stretched out.

27
Q

What is red shift

A

Wavelengths of light emitted from far away objects are shifted towards red (longer wavelength)

28
Q

Relation between red shift and distance

A

directly proportional

29
Q

How does the light emitted from distant galaxies appear in comparison with
light emitted on the Earth

A

redshifted

30
Q

What theory does redshift support
why?

A

Big bang theory

This means that galaxies are receding (in order to be red shifting)

Hence the unvierse is expanding

31
Q

What does the big bang theory state

A

Universe began billions of years ago (13 to 15 bn) when a hot superatom called erupted into a burst of energy

32
Q

2 evidence that support the big bang

A

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

33
Q

Full form of CMBR

A

Cosmic microwave backgrnd rad

34
Q

Formula for Hubble Constant

A

V/D

v = speed at which galaxies are moving away from earth
d = distance of galaxies from earth

35
Q

Value of hubbles constant

A

2.3 * 10^-18 per second

36
Q

hubble constant and time eqn

A

Hubble constant = 1 / time

37
Q

Age of universe eqn

A

age of universe = 1 / hubbles constant

which is roughly 13.8 seconds

38
Q

what is redshift used to calculate

A

speed at which the galaxy is moving away from the earth

39
Q

Why do we see the moon

A

Surface reflects sunlight

40
Q

How do we see the full moon

A

Whole sunlit side of the moon faces us

41
Q

Why can we only see part of the moon usually

A

usually only part of the sunlit side faces us, the rest is shadow

42
Q

Stages of moon

A

new moon - full shadow
waxing crescent
first quarter
waxing gibbous
full moon
waning gibbous
third quarter
waning crescent

43
Q

Amount of moon and shadow in

crescent
gibbous

A

crescent - 3/4th shadow, 1/4h moon

gibbous - 1/4th shadow, 3/4th moon

44
Q

Which side is shadow in

‘waxing’
‘waning’

A

waxing - shadow left side

waning - shadow right side

45
Q

describe shadow and moon in
new moon
full moon
quarters

A

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

46
Q

thing to remember about moon

A

shadow goes from left to right as the month progresses

Physics (25 decks)

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