Astrophysics Flashcards

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1
Q

For a single lense to make an image appear to be diminished, where should the object be placed?

A

Beyond 2f

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2
Q

For a single lense to make an image appear the same size, where should the object be placed?

A

At 2f

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3
Q

The a single lens to make an image appear magnified, where should the object be placed?

A

Between f and 2f

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4
Q

For a single lens to make an image appear as a virtual object, where should the object be placed?

A

Below f

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5
Q

How does a CCD work?

A

1- a CCD is a silicon chip, divided into picture elements (pixels)
2- each pixel is associated with a potential well in the silicon
3- photons are incident on the CCD, and the photons within the semi-conductor cause the electrons to be released
4- the number of electrons liberated, is proportional to the intensity of the light
5- the electrons are trapped in the potential wells, and an electron pattern is built up that is identical to the image formed on the CCD
6- when the exposure is complete, the charged is processed to form an image

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6
Q

What is meant by quantum efficiency, and what are the values for a CCD vs the human eye?

A

Number of photons detected/ number of photons incident
CCD: 80% or more
Human eye: 1%

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7
Q

What is chromatic abrasion, and which type of telescope does it effect?

A

A colour distortion that creates an outline of unwanted colour along the edges of objects in photos, that effects refracting telescopes. (Blue first then red)

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8
Q

What is spherical abrasion, and what type of telescope does it effect?

A

It occurs when the mirror isn’t a perfect parabola, and it effects both types of telescope

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9
Q

What is the Rayleigh criterion?

A

2 objects will just be resolved when the first minimum in the diffraction pattern of one image coincides with the central maximum of the other

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10
Q

How can you improve resolving power?

A

Increase the size of the dish, or look at smaller wavelengths

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11
Q

State 3 optical advantages of reflecting telescopes over refracting telescopes

A
  • mirrors don’t refract light, so they don’t suffer chromatic abrasion
  • mirrors can be larger, and therefore have greater resolving power
  • mirrors can be larger, and therefore have smaller minimum angular resolution
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12
Q

What is the maximum size of imperfections in a telescope dish can be?

A

Wavelength/ 20

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13
Q

What is 1 parsec?

A

The distance at which 1 AU subs tends an angle of 1 arc second

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14
Q

What is 1 arc second in degrees?

A

1/3600

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15
Q

What is meant by apparent magnitude?

A

The brightness of a star as seen from earth

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16
Q

What is meant by absolute magnitude?

A

The brightness of a star as seen from 10 pc away

17
Q

What is a standard candle?

A

Objects who’s absolute magnitude is known

18
Q

What is a black body?

A

And object that absorbed and emits all wavelengths of light

19
Q

What are hydrogen balmer lines?

A

Spectral lines corresponding to the visible wavelengths absorbed when electrons move from n=2 to higher energy levels

20
Q

Give a brief explanation of the key stages of the evolution of a sun like star

A
  • dust and gas is drawn together via gravity to form a protostar
  • protostars continue to contract and heat up until the core is hot enough to fuse hydrogen into helium (core hydrogen burning)
  • hydrogen in the core runs out, core contracts and heats up. Outer layers expand and cool, star becomes red giant
  • shell starts fusing hydrogen into helium (shell hydrogen burning)
    Hydrogen runs out, the core contracts and heats up. Helium now fuses into carbon and oxygen (core helium burning)
  • helium in the core runs out, core contracts and heats up
  • shell starts fusing helium (shell helium burning)
  • for a sun like star, once fuel has run out, it contracts into a hot dense core, throwing off outer layers
  • it has become a white dwarf
21
Q

For what mass of a star will the core contract to a white dwarf/ neutron star/ black hole?

A

1-1.4 solar masses: white dwarf
1.4-3 solar masses: neutron star
>3 solar masses: black hole

22
Q

What is a supernova?

A

A star whose luminosity increases enormously due to it exploding

23
Q

What is a neutron star?

A

A star with the density of nuclear matter

24
Q

What is a black hole?

A

An object with an escape velocity greater than the speed of light

25
Q

What is the schwarzchild radius?

A

The point at which the escape velocity is equal to the speed of light

26
Q

What is the Doppler effect?

A

The apparent change in frequency of a wave as a result of relative motion between the source and the observer

27
Q

What is the cosmological principle?

A

On a large scale, the universe is homogenous and isotropic

28
Q

What are the 3 pieces of evidence for the Big Bang?

A

1- red shift of galaxies
2- cosmic microwave background radiation
3- relative abundance of helium and hydrogen