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Physics > 8) Astrophysics > Flashcards

8) Astrophysics Flashcards

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1
Q

Units: mass, distance, velocity, acceleration, force, time, gravitational field strength

A

-Mass: kilogram (kg)
-distance: metre (m)
-velocity: metre per second (m/s)
-acceleration: metre per second squared (m/s2)
-Force: newton (N)
-time: second (s)
-gravitational field strength: newton/kilogram (N/kg)

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2
Q

The universe

A

Large collection of billions of galaxies

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3
Q

A galaxy

A

Large collection of billions of stars

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4
Q

Why does gravitational field strength vary

A

-the greater the mass of the planet, the greater its gravitational field strength, larger attractive force towards the centre of the planet or moon

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5
Q

Gravitational field strength on earth vs other planets

A

Earth: approximately 10 N/kg
Moon: less than earth - easier to lift a mass on the surface of the moon than on Earth

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6
Q

Gravitational force

A

Provides a force that is pulling smaller bodies towards a star or planet
-gravitational force exerted by the larger body on the orbiting object is always attractive
-force always acts towards the centre of the larger body
-causes the body to move and maintain a circular path

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7
Q

Different astronomical orbits - planets, moons, comets, artificial satellites

A

-planets orbit the Sun
-moons orbit planets
-comets orbit the Sun
-artificial satellites orbit the Earth or any body in the Solar System

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8
Q

Similarities in the way different planets orbit the Sun

A

-orbits are all slightly elliptical with the Sun at approximately the centre of the orbit
-all orbit in the same plane
-all travel in the same direction around the Sun

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9
Q

Differences in the way different planets orbit the Sun

A

-different orbital radius
-different speeds
-different orbital periods

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10
Q

Orbits of moons

A

-Moons orbit planets in a circular path
-Some planets have more than one moon
The closer the moon is to the planet:
-The shorter the time it will take to orbit
-The greater the speed of the orbit

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11
Q

Orbits of comets

A

Orbits are highly elliptical (very stretched) or hyperbolic
-Not all comets orbit in the same plane/ direction as the planets
-As the comet approaches the sun, its speed increases - in order to maintain a stable orbit or it will be sucked into the object it is orbiting
-As it moves further away from the sun, its speed decreases

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12
Q

Calculating orbital speed

A

The time taken for an object to complete one orbit

velocity (m/s) = 2π radius (m)/ orbital period (s)

v= (2πr)/T

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13
Q

Classification of stars

A

-warm objects emit infrared light
-extremely hot objects emit visible light
-colour they emit depends on how hot they are related to their surface
-astronomical objects cool as they expand, heat up as they contract
blue (hottest) –> white –> yellow –> red (coolest)

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14
Q

Life cycle of stars similar mass to the sun

A
  1. Nebula
  2. Protostar
  3. Main sequence star
  4. Red giant
  5. White dwarf
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15
Q

Life cycle of stars similar mass to the sun - nebula

A

All stars form from a giant cloud of hydrogen gas and dust called a nebula

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16
Q

Life cycle of stars similar mass to the sun - protostar

A

The force of gravity within a nebula pulls the particles closer together until it forms a hot ball of gas - Protostar
-density increases
-more frequent collisions
-temperature increases

17
Q

Life cycle of stars similar mass to the sun - main sequence star

A

-Protostar becomes hot enough, nuclear fusion occurs within its core- hydrogen to helium
-thermal expansion due to fusion occur
-force of gravity keeps star in equilibrium
-inward force of gravity = outward pressure force from the expanding hot gases

18
Q

Life cycle of stars similar mass to the sun - red giant

A

-After several billion years - hydrogen causing the fusion reactions start to run out
-core shrinks and heats up as the inward force due to gravity > outward force as pressure decreases
-A new series of reactions occur (helium to beryllium)
-As the core shrinks, reactions cause outer part to expand
-Becomes a red giant -red as the outer surface starts to cool

19
Q

Life cycle of stars similar mass to the sun - white dwarf

A

-The star will eventually become unstable
-The core which is left behind will collapse completely, due gravity, becomes white dwarf
-cools, amount of energy emitted decreases

20
Q

Life cycle of large stars

A
  1. Nebula
  2. Protostar
  3. Main sequence star
  4. Red super giant
  5. Supernova
  6. neutron star/ black hole
21
Q

Life cycle of large stars - red super giant

A

-After several billion years - hydrogen causing the fusion reactions start to run out
-core shrinks and heats up as the inward force due to gravity > outward force as pressure decreases
-A new series of reactions occur (helium to beryllium)
-As the core shrinks, reactions cause outer part to expand, becomes red super giant

22
Q

Life cycle of larger stars - supernova

A

-fusion reactions finish
-the core of the star will collapse causing a gigantic explosion - supernova

23
Q

Life cycle of larger stars - neutron star

A

-At the centre of this explosion (supernova) a dense body - neutron star - will form

24
Q

Life cycle of larger stars - black hole

A

-In the case of the largest stars, the neutron star will continue to collapse under the force of gravity until it forms a black hole
-A black hole is an extremely dense point in space that not even light can escape from

25
Q

Absolute magnitude

A

Astronomers use this to measure the brightness of stars at a standard distance (if they were all the same distance from earth)
-scale runs back to front: brighter, smaller magnitude

26
Q

Brightness of a star

A

-the amount of light the star emits
-how far away the star is

27
Q

Hertzsprung-russel diagram

A

-increasing luminosity compared to the sun (y-axis)
-decreasing temperature (x-axis)

-most stars lie on the main sequence
-white dwarfs dimmer and hotter than red giants
-red giants are brighter and cooler than white dwarfs

-draw it

28
Q

The Big Bang theory

A

-14 billion years ago, the Universe began from a very small region that was extremely hot and dense
-there was a giant explosion - big bang
-caused the universe to expand from a single point, cooling as it does so, to form the universe today
-universe continues to expand

29
Q

Absorption spectra

A

-longer wavelength - red
-shorter wavelength - purple
All wavelengths of visible light are emitted from the sun towards earth
-sun’s atmosphere contains lots of different chemicals and some of them can absorb certain wavelengths of light
-when light reaches earth, certain wavelengths are missing, absorption spectra ends up with a pattern of dark lines

30
Q

Galactic red shift

A

-when we analyze light from distant galaxies, their absorption spectras have the same pattern as for the sun but shifted towards red end - red shift
-distant galaxies emitting light are moving away from earth so as waves are travelling towards us, they are stretched

31
Q

Doppler effect

A

The apparent change in the frequency/ wavelength of a wave due to the relative motion of the source and observer
-coming towards you, wavelengths are shorter, galaxy moving towards, blue shift
-going away from you, wavelengths are stretched, galaxy moving away, red shift

32
Q

How does doppler effect prove big bang theory

A

-space between us and galaxy are expanding
-all galaxies are moving away from earth and each other
Expected after an explosion
-some matter is light, greater speed, further from source of explosion
-some matter is heavier, slower speed, closer to source

33
Q

Cosmic Microwave Background Radiation (CMBR)

A

-observe that distant galaxies are receding away, so universe is expanding so single point in the beginning
-where there would be very high energy gamma waves
-as universe expanded, the high energy gamma waves with short wavelengths would be stretched
-to x-rays, UV rays, visible light, infrared, and finally microwaves
-which we now observe from all directions in the universe

Physics (8 decks)

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