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Physics Paper 2 > Space > Flashcards

Space Flashcards

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1
Q

What is the Astronomical Unit?

A

The astronomical unit is the mean distance between the Earth and the Sun.
1AU = 1.5X10¹¹m

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2
Q

What is the unit of a light year a measure of?

A

Distance

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3
Q

What is a light year?

A

The distance that light travels in a year
1ly = 9.46 x10¹⁵ m

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4
Q

What can parallax be used for?

A

To calculate distances in space, using observations and trigonometry

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5
Q

What is a parsec?

A

A parsec is an astronomical unit of distance. A star is one parsec (pc) away from the Earth if the parallax angle is one arcseond

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6
Q

What is a Hertzsprung-Russell diagram?

A

A H-R diagram is a plot of a star’s stellar luminosity against its surface temperature

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7
Q

What category of star is represented by the main diagonal on a H-R diagram?

A

Main Sequence

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8
Q

What category of stars lie below the main sequence diagonal on a H-R diagram?

A

White Dwarfs

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9
Q

What categories of stars lie above the main sequence diagonal on a H-R diagram?

A

Red giants and red supergiants

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10
Q

State the equation linking the instensity, luminosity and distance of a star

A

I = L / 4πd²

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11
Q

What is the doppler effect?

A

The apparent change of wavelength as a result of relative movement between a receiver and source

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12
Q

What happens to the observed wavelength of a wave when a source is moving away from the observer?

A

The observed wavelength increases

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13
Q

What happens to the observed wavelength of a wave when a source is moving towards the observer?

A

The observed wavelength will decrease

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14
Q

What happens to the observed frequency of a wave when a source is moving towards the observer?

A

The observed frequency will increase

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15
Q

What is red-shift?

A

The apparent shift of the wavelength of light emitted by a star towards the red end of the light spectrum, as a result of it receding from the observer

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16
Q

What equations are used to calculate red-shift?

A

z = Δλ/ λ ≈ Δf/ f ≈ v/ c

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17
Q

Describe how the relative speed value inputted into the equation (red shift equation) differs depending on whether the source and receiver are nearing or receding.

A

For receding, the value is positive.
For nearing, the value is negative

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18
Q

What is the difference between a positive and a negative z value?

A

Positive means reshift is happening, the objects are receding from one abother. A negative value represents blue shift, objects are getting closer

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19
Q

What are the two main conclusions that can be drawn from observations of red shift from distant galaxies?

A
  1. All galaxies show red shift and so all galaxies are moving away
  2. The more distant a galaxy is, the greater its red shift and so the faster it is receding
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20
Q

What does the red-shift of distant galaxies provide evidence for?

A

Red-shift of distant galaxies suggests that they are moving away from us. This supports the concept that the univers is expanding, which supports the Big Bang theory

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21
Q

What does CMBR stand for?

A

Cosmic Microwave Background Radiation

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22
Q

How does the existence of CMBR support the Big Bang theory?

A

In the big bang, lots of high energy radiation was produced. As the universe has expanded over time, the wavelength of this radiation has been ‘stretched’ so that it is now in the microwave region. Other theories of the universe can’t account for the existence of CMBR

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23
Q

What is cosmic microwave background radiation?

A

Radiation in the microwave of the Em spectrum that is present in very small quantities all around us

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24
Q

What is the Big Bang theory?

A

A theory for the formation of the universe. it proposes that the universe began from a very small, hot and dense region, and expanded from this point.

25
Q

What two quantities does Hubble’s law relate?

A

The distance of a galaxy to the speed at which it is moving away

26
Q

Explain Hubble’s law in words

A

The speed at which a galaxy is moving away from us is directly proportional to the distance it is away

27
Q

State the defining equation for Hubble’s law.

A

v = H0 d
H0 is Hubble’s constant

28
Q

Describe what was observed when observations of galaxies’ brightnesses were compared to the predicitions made by Hubble’s Law.

A
  • The actual and predicted brightnesses of distant galaxies don’t always agree with each other
  • Distant galaxies aren’t as bright as predicted by Hubble’s Law, suggesting that they are more distant than predicted
29
Q

State the conclusion that can be made from Hubble’s Law and observations

A

The rate of expansion of the universe is accelerating, since galaxies are further away than predicted.

30
Q

give one possible explanation for the acceleration of the universe’s expansion.

A

The existence of dark energy. This would explain where the energy required for the expansion rate to constantly accelerate comes from.

31
Q

Why is the existence of dark energy still only a hypothesis?

A

Dark matter and energy can’t be easily observed

32
Q

What has led scientists to believe in the existence of dark matter?

A

When measuring the rotational speed of the stars in our galaxy, the mass suggested is way too small to keep the galaxy spinning, so they must contain a lot of unseen matter that does not emit light

33
Q

Why is it difficult to know the exact value of Hubble’s constant?

A

It is very difficult to get an accurate measurement for a galaxy’s velocity and its exact distance from Earth. There is a lot of variation in vlaues of H0 depending on various methods

34
Q

What is the Stefan-Boltzmann equation ?

A

L = 4πr²σT⁴ (for a sphere)
L = σAT ⁴
L is luminosity, σ is Stefan constant, T is temperature K, A is surface area m^2

35
Q

Why do hotter stars more blue whereas cooler stars redder?

A

Hot stars show very little hydrogen and most of the hydrogen is in the form of plasma so cannot absorb or emit light. As temp cools, hydrogen can hold onto an electron, so cooler stars are able to absorb more light, relating to the redder colour of the star

36
Q

What is the differene between brightness and luminosity?

A

Luminosity is the true brightness of a star wgich is their power output whereas brightness is the object’s apparent birghtness meaured from Earth

37
Q

What is Wien’s law?

A

λmaxT = 2.898 × 10⁻³ m K
peak wavelength x Temp (K) = 2.898x10⁻³

38
Q

Describe the relationship between peak wavelength and temperature

A

As the temperature increases, the overall radiated energy increases and the peak wavelength decreases

39
Q

What happens if the density of matter in the universe is less than the critical density?

A

The universe will expand forever, there isn’t enough gravitational pull from the material to stop/reverse the expansion. known as the ‘Big Chill’ or ‘big Freeze’ as it slwoly cools as it expands until it is unable to sustain life

40
Q

What does the inverse sqaure law tell us?

A

It tells us that the energy emitted by a star will spread out in all directions over the surface of an increasing sphere

41
Q

What are standard candles?

A

Objects of known luminosity

42
Q

What is an arcsecond?

A

An angle equal to 1/3600 th of a degree

43
Q

What is the critical density

A

The avergae density of matter required for the universe to just halt its expansion

44
Q

Why can we only use parallax to measure distances less than 100 lightyears?

A

Beyond 100 light years it becomes very hard to measure as the parallax angle is very small and so the measurement error becomes too big

45
Q

What is the absorption spectrum?

A

A spectrum of EM radiation, transmitted through a substance showing dark lines when light is absorbed at particular wavelengths

46
Q

For objects too far to be measured using parallax what can you do?

A

You can use ‘standard candles’ to estimate how far away it is from Earth by how bright it appears

47
Q

What is a perfect black body?

A

A theoretical object which absorbs ALL the radiation tha falls on it, doesn’t reflect or transmit any radiation

48
Q

What are the 3 possible outcomes for the universe?

A

Open universe
Flat universe
Closed universe

49
Q

How do you get from degress to kelvin?

A

add 273.15

50
Q

Describe a ‘closed’ universe.

A

A closed universe will happen if the density is high. Locally parallel light rays converge at a distant point = spherical geometry

51
Q

What is absolute magnitude?

A

The brightness of a celestial object as it would be seen at a distance of 10 parsecs

52
Q

Describe a flat universe.

A

When the density equals the critical density, creates a flat universe where parallel rays remain parallel

53
Q

How does trigonometric parallax work?

A

You measure the angle of a relatively nearby star close to earth, and observe how it changes as the position of the Earth changes. Measure the angle 6 months apart (so 2AU apart), we can then use trigonometry to calculate the distance to the star

54
Q

What are cephied variables?

A

Stars that brighten and dim periodically

55
Q

How can Hubble’s Law be used to estimate the age of the universe?

A

time = distance / velocity
Ho = v/d
Age of universe is 1/Ho

56
Q

Define luminosity.

A

the rate at which energy of all types is radiated by an object in all directions

57
Q

What happens if the density of matter in the universe if greater than the critical density?

A

If greater then gravity will slow the expansion till it stops and collapses back on itslef - the ‘Big Crunch’

58
Q

Describe an open universe

A

When the density is low, locally parallel raus will diverge to cause an open universe

Physics Paper 2 (7 decks)

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