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A2 Physics > Astronomy > Flashcards

Astronomy Flashcards

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1
Q

What is the quantum efficiency of a CCD?

A

The percentage of photons incident on the chip that initiate a detectable response.

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2
Q

What is a common quantum efficiency of a CCD?

A

80%

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3
Q

What is the advantage of higher sensitivities found in CCDs?

A

Exposure times are reduced.

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4
Q

What is the dynamic range of a CCD?

A

Approx 100,000 which corresponds to 14.5 magnitudes.

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5
Q

Give five advantages of using CCDs over photographic film.

A
  • High sensitivity
  • Larger dynamic range
  • Linear exposure
  • Broad range of wavelengths can be detected
  • Can be interfaced directly with computers allowing complete automation
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6
Q

How does a CCD work?

A
  • A CCD is a semiconductor chip sensitive to light divided into discrete rectangular areas (pixels).
  • Each pixel is made up of 3 electrodes with the central electrode having a potential of 10V and the two outer electrodes 2V.
  • This forms a depletion layer at the PN junction with a potential well beneath the central electrode.
  • Lights photons cause electrons to be released into the potential well.
  • The amount of charge collected is directly proportional to the number of photons falling on each pixel.
  • The potential of each electrode is changed in order to move the electrons along the CCD causing them to leave as a current pulse.
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7
Q

How can noise be reduced in images?

A

Cooling the CCD or photographic film.

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8
Q

How is a colour image produced from a CCD?

A

Combining images from a red, green and blue filter

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9
Q

What are the two “windows” in the atmosphere know as?

A

Optical and radio windows

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10
Q

What types of EM radiation can pass through the atmosphere?

A

UV, IR, visible light, radio

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11
Q

What causes long wavelength UV to be absorbed in the atmosphere?

A

Ozone

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12
Q

What causes light and IR and visible light to be absorbed in the atmosphere?

A

O2, H2O, CO2

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13
Q

Where can UV astronomy take place?

A

Above the Earth’s atmosphere

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14
Q

What can IR astronomy be used for?

A
  • Finding exoplanets
  • Observing nebulae
  • Observing after-effects of gamma ray bursts
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15
Q

What can UV astronomy be used for?

A
  • Star formation rate

- Analysing quasars

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16
Q

What can X-ray astronomy be used for?

A
  • Finding black holes

- Observing stellar remnants

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17
Q

What is the strongest source of radio waves found on Earth?

A

The Sun

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18
Q

What is the window of wavelengths for radio waves?

A

1cm to 15m

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19
Q

What are the three main mechanisms of celestial radio emission?

A
  • Thermal
  • Synchrotron radiation
  • Hydrogen emission
20
Q

What is a black body?

A

An object that absorbs all radiation and can therefore emit at all possible wavelengths.

21
Q

How can a telescope be made bigger without increasing the size of the dish?

A

Having multiple telescopes placed over a large distance which produces a telescope effectively of the size of the distance between them.

22
Q

How is a radio map produced?

A

Placing the telescope at an angle then allowing the Earth to rotate then changing the angle.

23
Q

When can wire mesh be used for a telescope?

A

When the wavelength of the radiation being measured is over 20x the mesh size.

24
Q

What is the annual parallax of a star?

A

Half the angle through which the direction of the star shifts as the Earth moves from one side of orbit to the other.

25
Q

How is the distance from Earth in parsecs calculated?

A

1 / annual parallax in arc seconds

26
Q

What is the greatest distance trigonometric parallax can be used for?

A

100pc

27
Q

What is an arc second in degrees?

A

1/3600

28
Q

What is a black body?

A

A body that absorbs all radiation that falls on it so is able to emit at all wavelengths.

29
Q

What is black body radiation?

A

The spectrum of EM waves emitted.

30
Q

What does the spectral distribution of a black body depend on?

A

The surface temperature of the body.

31
Q

What does the area under a wavelength vs. intensity graph give?

A

Total energy radiated per unit time per unit surface area or power per unit area

32
Q

What does E stand for in E=σT^4?

A

Power radiated per square metre

33
Q

How is the total power emitted by a star calculated?

A

P = AσT^4

34
Q

What is the apparent magnitude of a star?

A

A measure of brightness as seen from Earth.

35
Q

What ratio of apparent luminosity does a difference of magnitude 2.5 give?

A

10

36
Q

What ratio of apparent luminosity does a difference of magnitude 5 give?

A

100

37
Q

What is the absolute magnitude of a star?

A

A measure of the brightness of the star if the star was moved to 10pc from Earth.

38
Q

What causes a continuous emission spectra?

A

Multiple compounds and molecules emitting EM waves.

39
Q

What causes discrete emission spectra?

A

Excited electrons returning to lower energy levels causing energy to be released at discrete wavelengths.

40
Q

What causes absorption lines in emission spectra?

A

Discrete wavelengths of light travelling in one direction being absorbed by a compound then emitted isotropically.

41
Q

What is the order of spectral classes of stars?

A

OBAFGKM

42
Q

What is the origin of prominent absorption lines in cooler stars?

A

Molecules

43
Q

What is the origin of prominent absorption lines in type A-G stars?

A

Large elements since most molecules have been broken down by the increased temperature.

44
Q

What is the life cycle of a star of one solar mass?

A

Dust cloud - Main sequence yellow star - red giant - white dwarf

45
Q

What is the life cycle of a star of ten solar masses?

A

Dust cloud - blue/white main sequence - red supergiant - supernova - neutron star

46
Q

What is the life cycle of a star of 30-50 solar masses?

A

Dust cloud - blue/white main sequence - red supergiant - supernova - black hole

A2 Physics (9 decks)

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