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Exploring The Cosmos 1Y > Mapping the Universe > Flashcards

Mapping the Universe Flashcards

1
Q
  1. Which of the following statements is true?

A. blue light has a shorter wavelength than red light

B. green light has a lower frequency than red light

C. red light has a shorter wavelength than green light

D. blue light has a lower frequency than red light

A

A. blue light has a shorter wavelength than red light

ROYGBIV
long–>short wavelength
low –> high energy
low–> high freq.

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2
Q

“Diffraction” means

A. the change of direction of light when it enters or leaves a medium

B. the pattern of light and dark that arises when waves of different phases combine

C. the spreading of light waves when they encounter an obstacle

D. the reduction in the intensity of light as it passes through a medium

A

C. the spreading of light waves when they encounter an obstacle

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3
Q

In which part of the spectrum do we find light with a wavelength of 2 microns (i.e. 2000 nm)?

A. radio
B. infra-red
C. visible
D. ultraviolet

A

B. infra-red

GAMMA RAYS - X RAYS - UV - IR - MICROWAVES - RADIO (GXUIMR)

long–>short wavelength
low –> high energy
low–> high freq.

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4
Q

The Hubble Space Telescope is placed above the Earth’s atmosphere so that

A. it can detect radio waves
B. it can detect X-rays
C. it does not suffer from radio interference
D. it does not suffer from distortions due to atmospheric turbulence

A

D. it does not suffer from distortions due to atmospheric turbulence

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5
Q

Which sort of telescope combines a curved mirror with a corrector plate?

A. Newtonian reflector
B. Cassegrain reflector
C. refractor
D. Schmidt telescope

A

D. Schmidt telescope

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6
Q

In which part of the spectrum can we use a scintillator (substances that emit fluorescence when exposed to radiation such as X-rays and γ-rays) as a detector?

A. Infra-red
B. visible
C. X-ray
D. radio

A

C. X-ray

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7
Q

The Chandra Telescope is placed above the Earth’s atmosphere so that

A. it can detect radio waves
B. it can detect X-rays
C. it does not suffer from radio interference
D. it does not suffer from distortions due to atmospheric turbulence

A

B. it can detect X-rays

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8
Q

What causes “chromatic aberration”?

(-Lenses focus different colours at different points
-It is hard to get a good image across many colours
-Can use filters to look at a single colour or use lenses of composite materials)

A

The wavelength-dependence of refraction in a telescope lens

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9
Q

What is detected by the IceCube experiment in Antarctica?

A. X-rays from the Sun
B. dark matter particles
C. neutrinos from supernovae and other energetic phenomena
D. changes in Earth’s climate

A

C. neutrinos from supernovae and other energetic phenomena

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10
Q

In which part of the spectrum does the Fermi Space Telescope operate?

A. ultra-violet
B. X-rays
C. gamma-rays
D. infra-red

A

C. gamma-rays

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11
Q

What is meant by “chromatic aberration”? Which of the two types of telescope mentioned above
suffers from it, and why? (2)

A

-The distortion of detail in an image that results because light of different wavelengths
changes direction by different amounts when it passes from air into glass and out again (1 mark).

-Thus all colours will not come to a sharp focus at exactly the same distance along the axis of the instrument. Images suffering
from chromatic aberration will show “false colour”. (1 mark)

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12
Q

Explain why all the biggest telescopes are reflecting rather than refracting telescopes. (2)

A

As lenses get bigger they also get thicker so they inevitably involve more and more absorption of light in the lens(1).

Since they must be supported only at the outer rim they become more and more susceptible to deformation under gravity (1).

Mirrors do not involve light passing through a glass object and they can easily be supported
from underneath much more securely.

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13
Q

Explain how we can fabricate a telescope that operates in the X-ray part of the spectrum. (2)

A

X-rays impinging normally on a mirror will simply pass through the material of the mirror. However X-rays meeting a mirror at grazing incidence (1 mark),

at a very large angle to the normal, can be reflected enabling the
construction of a mirror. Segments of a parabola can be constructed operating at grazing incidence, and several such segments nested to provide enough effective area. (1 mark)

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14
Q

The sky appears blue during the day because of

A. Atmospheric scattering
B. Atmospheric pollution
C. Atmospheric refraction
D. Atmospheric absorption

A

A. Atmospheric scattering

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15
Q

Active optics are used in modern telescopes to change

A. The detector sensitivity for measuring different wavelengths.

B. The focal length of the primary mirror for different astronomical objects.

C. The shape of the primary mirror to correct for atmospheric disturbances.

D. The direction of the telescope to track a star across the night sky.

A

C. The shape of the primary mirror to correct for atmospheric disturbances.

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16
Q

Wave-particle duality describes how light behaves

A. As neither a wave or a particle
B. As both a wave and particle
C. As a wave but not a particle
D. As a particle but not a wave

A

B. As both a wave and particle

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17
Q

A telescope suffering from chromatic aberration will

A. Focus monochromatic light rays at different distances from the optical axis to different points
B. Focus monochromatic light rays at different angles to the optical axis to the same point
C. Focus different wavelengths at different distances
D. Be limited by the Earth’s atmosphere

A

C. Focus different wavelengths at different distances

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18
Q

Which one of the following statements is true?

A. Different parts of the spectrum provide different information about a particular source.
B. Light travels at different speeds at different wavelengths in vacuum
C. Stars emit mainly ultraviolet radiation.
D. Visible light is hard to detect on Earth.

A

A. Different parts of the spectrum provide different information about a particular source.

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19
Q
A
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20
Q

Large ground-based observatories, such as VLT, are

A. Not able to move or track objects in the sky
B. Able to move on one axis only
C. Able to move and track objects in the sky using a equatorial mount
D. Able to move and track objects in the sky using an altitude-azimuth mount

A

D. Able to move and track objects in the sky using an altitude-azimuth mount

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21
Q

Located under a mountain in Japan, Super Kamiokande is used by scientists to detect

A. X-rays
B. gravitational waves
C. infrared light
D. neutrinos

A

D. neutrinos

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22
Q

The energy of a photon can be expressed by

A. E=cλ.
B. E=f/λ.
C. E=hf.
D. E=hc.

A

C. E=hf

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23
Q

The resolving power of a radio telescope can be increased by:

A. making observations during the night.
B. putting the telescope on a mountain.
C. increasing the diameter of the primary mirror.
D. decreasing the diameter of the primary mirror.

A

C. increasing the diameter of the primary mirror.

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24
Q

A Newtonian telescope is

A

a reflecting telescope

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25
Q

Describe the atmospheric absorption process for x-rays (4)

A

X-rays have enough energy to kick electrons out from molecules. An x-ray photon incident upon a molecule can collide with an electron, sending the electron out of the molecule at high speed. (1)

During this process, the x-ray can either be consumed as it imparts its entire energy to the electron (photoionisation), (1)

NOTE: naming “photoionisation” not necessary but useful for later explanations)

Or it can itself scatter into a different direction at a longer wavelength (Compton scattering) (1),

NOTE: naming “Compton scattering” not necessary but useful for later explanations)

In the Compton scattering, the scattered x-ray must, due to the principle of conservation of energy, have less energy than the initial x-ray, as it must impart sufficient energy to an electron to allow it to escape from the molecule. That means the energy left over in the photon after the collision is lower, and hence it must exit with a lower frequency and longer
wavelength. (1)

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26
Q

Describe the principles behind a grazing incidence telescope and explain why it is used to focus
x-rays for astronomical observations. (3)

A

The wavelength of x-rays is small enough that it is comparable to the spacing between atoms in solids. So, x-rays will pass through a conventional mirror and not be reflected. (1)

A grazing incidence telescope is created by positioning the atomic lattice structure of the solid such that incident x-rays impinge at a large angle to the structure’s normal (1)

At extreme angles, the material appears to be more dense than at shallow angles, allowing x-rays to be reflected and, therefore, focused. (1)

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27
Q

The speed of light is equal to

A. the wavelength divided by the frequency
B. the wavelength plus the frequency
C. the wavelength minus the frequency
D. the wavelength multiplied by the frequency

A

D. the wavelength multiplied by the frequency
s = wave. x freq

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28
Q

The colour of visible light is determined by its

A. amplitude
B. frequency
C. wavelength
D. energy

A

C. wavelength

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29
Q

The magnification of a lens with objective focal length of 10 cm and eyepiece focal length 10 cm is

A

1

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29
Q

The effect of diffraction is most apparent when the size of the object is

A. much greater than the incident wavelength
B. much greater than the incident energy
C. similar to the incident wavelength
D. similar to the incident energy

A

C. similar to the incident wavelength

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30
Q

Adaptive optics are needed in ground-based telescopes to correct for

A. atmospheric refraction
B. atmospheric absorption
C. atmospheric emission
D. atmospheric reflection

A

A. atmospheric refraction

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31
Q

To be effective for astronomy, mid-infrared and far-infrared telescopes must be placed

A. on the Earth’s surface
B. in space
C. under ground
D. under water

A

B. in space

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32
Q

To increase the brightness of a telescope’s image, it needs

A. a large diameter
B. a small diameter
C. a large magnification
D. a small magnification

A

A. a large diameter

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33
Q

The LIGO gravitational wave telescopes in the USA have arms with length

A. 4 metres
B. 40 metres
C. 400 metres
D. 4000 metres

A

D. 4000 metres

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34
Q

Gravitational waves are NOT thought to be produced by

A. binary black hole systems
B. supernova explosions
C. symmetric rotating pulsars
D. asymmetric rotating pulsars

A

C. symmetric rotating pulsars

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35
Q

The Ice Cube telescope measures

A. temperature variations in cold stars
B. gravitational waves
C. neutrinos
D. gamma rays

A

C. neutrinos

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36
Q

Describe a way in which your chosen type of lens aberration can be avoided or corrected for (2)

A

(Chromatic aberration) Use two different lenses with complimentary chromatic aberrations. (1)

(Spherical aberration) Ensure that during the manufacturing process that the surface of the lens is shaped very
carefully. (1)

37
Q

Describe the effect of the Earth’s atmosphere that creates the need for adaptive optics in large ground-based observatories. (2)

A

The atmosphere refracts light (1), which distorts the image and

therefore diminishes the resolving power of the telescope (1).

38
Q

What other atmospheric effect can space-based telescopes avoid compared to ground-based telescopes, even those containing adaptive optics? (1)

A

The atmosphere blocks some wavelengths of light (1)

39
Q

Give the name of the successor to the Hubble Space Telescope, scheduled for launch in 2018. (1)

A

James Webb Space Telescope

40
Q

Wave-particle duality describes how light behaves

A

As both a wave and particle.

41
Q

The spectrum of light can be analysed by utilising both

A.diffraction and dispersion.
B.interference and dispersion.
C.refraction and interference.
D.diffraction and interference.

A

D.diffraction and interference

42
Q

If a telescope suffers from chromatic aberration it means

A

Different wavelengths are focused at different distances.

43
Q

The Hubble Telescope

A

is a space-based telescope sensitive to ultraviolet, visible and near-infrared light.

44
Q

The reason why the sky appears blue in daytime and sunsets appear red is because of

A

atmospheric scattering.

45
Q

Infrared photons have enough energy to

A

excite vibrational motion of molecules.

46
Q

Ultraviolet light is emitted by stellar objects with a temperature of

A

10,000 Kelvin

47
Q

To detect gamma rays what can be used?

A

scintillation crystals and photomultipliers can be used.

48
Q

What are most large ground-based observatories, such as Keck, VLT and Gran Telescopio Canarias able to do?

A

are able to move and track objects in the sky using an altitude-azimuth mount.

49
Q

Super Kamiokande, which is located under a mountain in Japan, is used by scientists to detect

A

neutrinos

50
Q

Which of the following statements correctly describes the wavelength of an electromagnetic wave?

A

The wavelength is the distance between two consecutive peaks.

51
Q

Interference between the light coming from different telescopes is used to

A

improve the resolution

52
Q

The phenomenon of dispersion is

A

the dependence of the speed of light on wavelength.

53
Q

Why can X-Rays penetrate inside solids?

A

They have very small wavelengths.

54
Q

What is the objective of a telescope?

A

It is the part which concentrates the light.

55
Q

Reflecting telescopes are not strongly affected by chromatic aberration because

A

there are no refractions.

56
Q

Diffraction gratings are used for

A

analysing the light spectrum.

57
Q

The detection of UV radiation is important astronomically because

A

part of the hydrogen spectrum is in the UV band.

58
Q

Which of the following uses a grazing incidence telescope?

A

Chandra

59
Q

LIGO is an acronym for:

A

Laser Interferometric Gravitational-wave Observatory

60
Q

The speed of light in a vacuum is approximately

A

300 million metres per second.

61
Q

The term ‘refraction’ is used to describe when light

A

changes direction when transmitting through different media.

62
Q

For an astronomical source, the focal length of a mirror is

A

the distance from the mirror to the focal point.

63
Q

Chromatic aberration can occur in a telescope because

A

light of different wavelengths are focussed to different positions.

64
Q

Light can be described as having a “dual” nature. What does this mean?

A

It behaves like a wave and a particle

65
Q

A Newtonian telescope is

A

a reflecting telescope.

66
Q

Astronomers hope to discover gravitational waves by

A

using laser interferometers

67
Q

During the day the sky appears blue because

A

the scattering of blue light is stronger than red light.

68
Q

Atmospheric absorption causes

A

dimming or extinction of certain wavelengths of light.

69
Q

The resolving power of a radio telescope can be increased by

A

increasing the diameter of the primary mirror.

70
Q

A Schmidt-Cassegrain telescope is one that has?

A

A corrector plate, a primary mirror and a secondary mirror

71
Q

Why are astronomers interested in measuring light at different parts of the electromagnetic spectrum?

A

Different parts of the spectrum provide different information.

72
Q

What does the frequency of light mean?

A

The number of times the wave cycle repeats every second.

73
Q

The energy of a photon can be expressed by

A

E=hf

74
Q

What is the purpose of the objective lens in a refracting telescope?

A

To focus the incoming light

75
Q

If a refracting telescope has an objective lens with a focal length of 300cm and has an
eyepiece with a focal length of 3cm, the magnification is?

A

M = 100.

76
Q

Active optics is used in modern telescopes to

A

change the shape of the primary mirror to correct for atmospheric disturbances.

77
Q

The Earth’s atmosphere is responsible for which three phenomena in observational
astronomy?

A

Atmospheric refraction, Atmospheric scattering, and Atmospheric absorption.

78
Q

For what reason is interferometry used when using multiple telescopes to observe
astronomical objects?

A

To increase the resolving power of the detector.

79
Q

Gravitational wave detectors aim to measure the radiation emitted by accelerating masses
by

A

using long-baseline laser interferometers.

80
Q

Name one telescope, currently in operation or under construction, which aims to detect gravitational radiation. [1]

A

LIGO (Laser Interferometer Gravitational Wave Observatory)

aLIGO
(advanced Laser Interferometer

Gravitational Wave Observatory)

GEO600

Virgo

TAMA.

81
Q

Explain how gravitational waves are produced and provide one potential source that ground-based telescopes could potentially observe. [3]

A

Gravitational waves are produced by accelerating mass. Potential sources of detectable gravitational waves include: binary systems (black-hole/black-hole, neutron star/neutron star, blackhole/neutron star), supernovae and rotating
non-axially-symmetric neutron stars.

82
Q

Describe, with the aid of a diagram, the operating principle of an interferometric gravitational wave detector. On your diagram you should indicate all optical components and state the approximate arm length. [6]

A

Modern gravitational wave detectors are based on a Michelson interferometer design, whereby laser light is incident onto a beam splitter which sends the light along two different paths, known as arms. At the end of each arm are mirrors
which reflect the light back to the beam splitter where it interferes. By
maintaining the length of each arm correctly, destructive interference occurs at the detector output and no signal is measured, however, if the relative arm lengths change then constructive interference occurs and a signal will be measured by the photodetector. A laser interferometer thus behaves like a large ruler. When a gravitational wave passes one arm will get shorter while the other arm will get longer and the effect is measured by monitoring the output of the detector.

+DIAGRAM

83
Q

What is an electromagnetic wave and which parameters are used to characterise it?

A

Electromagnetic waves are waves where the electric and magnetic field oscillate. (1 mark)

Characteristic parameters are: wavelength, amplitude, frequency, and speed. (2 marks)

84
Q

Give two examples of how the atmosphere of the Earth can affect the observations made by ground
based telescopes [2]

A

Atmospheric refraction causes light rays to be bent upon entering the atmosphere, is the reason for
twinkling of stars, and can move the positions of stellar objects on short timescales. (2 marks)

Atmospheric absorption means that the atmosphere is transparent for certain wavelengths/frequencies
and opaque for others wavelengths/frequencies. This results in the dimming or complete extinction of different portions of the EM spectrum. (2 marks)

Atmospheric scattering causes short wavelengths to be scattered more than long wavelengths. It is this reason the sky looks blue during the day and why sunsets look red. (2 marks)

85
Q

Name one space-based telescope, the type of electromagnetic radiation it was sensitive to and what instrumentation and/or design enabled it to sense this radiation.

A

Hubble Space Telescope - UV to NIR - Cassegrain design and CCD camera. (3 marks)

Infra-Red Astronomical Satellite (IRAS) - IR - Cassegrain design, very low resolution detector array (62 infrared detectors), low resolution spectrometer. (3 marks)

Infra-Red Space Observatory (ISO) - IR (2.5um to 240um wavelength) - Cassegrain design, high resolution
camera, diffraction spectrometers. (3 marks)

Spitzer - IR (3um to 180um wavelength) - Cassegrain design, infrared camera, infrared spectrometer. (3 marks)

International Ultraviolet Explorer (IUE) - UV (115nm - 350nm wavelength) - spectrometer using caesium tellurium cathode and modifed TV camera. (3 marks)

Far Ultraviolet Spectroscopic Explorer (FUSE) - UV (90nm - 120nm wavelength) - Diffraction spectrometer. (3 marks)

Chandra X-Ray Observatory - X-rays - grazing incidence mirrors, high resolution camera, advanced CCD imaging spectrometer, transmission grating spectrometers. (3 marks)

X-Ray Multi-mirror Mission-Newton (XMM-Newton) - X-Rays + partial UV - grazing incidence mirrors, CCD
cameras, spectrometers. (3 marks)

Compton Gamma-Ray Observatory (CGRO) - Gamma-Rays – scintillation detectors and spectrometers. (3
marks)

86
Q

Describe the operating principle of a laser interferometer (LIGO) with the aid of a diagram, naming the key optical components. [6]

A

Modern gravitational wave detectors are based on a Michelson interferometer design, whereby laser light is incident onto a beam splitter which sends the light along two different paths, known as arms. At the end of each arm are mirrors which reflect the light back to the beam splitter where it interferes. By maintaining the length of
each arm correctly, destructive interference occurs at the detector output and no signal is measured, however, if the relative arm lengths change then constructive interference occurs and a signal will be measured by the photodetector. A laser interferometer thus behaves like a large ruler. When a gravitational wave passes one arm
will get shorter while the other arm will get longer and the effect is measured by monitoring the output of the detector.

(Mark distribution: accurate description of operation for a gravitational wave detector [3], Accurate diagram of a Michelson interferometer with labels and typical arm lengths [3])

87
Q

Explain how gravitational waves are produced and state what the astronomical source of the recent
detection was or state what potential sources may be detected in the near future? [3]

A

Gravitational waves are produced by accelerating mass. The source of the recent detection was two black
holes (each approximately 30 solar masses) as they orbited each other and eventually merged. Potential sources of detectable gravitational waves include: binary systems (black-hole/black-hole, neutron star/neutron star, blackhole/neutron star), supernovae and rotating non-axially-symmetric neutron stars.

88
Q

Name one other gravitational wave detector which is currently in operation or is planned for the future. [1]

A

GEO600
Virgo
TAMA
KAGRA
LIGO-India
LISA

89
Q
A

Exploring The Cosmos 1Y (5 decks)

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