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Astronomy And Space Science > Spectroscopy, Telescopes > Flashcards

Spectroscopy, Telescopes Flashcards

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1
Q

What is a blackbody?

A

A blackbody is an ideal object that does not reflect any light and thus emits electromagnetic radiation in all wavelengths entirely as a result of its temperature.

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2
Q

What is blackbody radiation?

A

Refers to the light emitted by a blackbody.

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3
Q

What is Wein’s Law?

A

The blackbody radiation consists of a continuous spectrum that peaks at a certain wavelength. This wavelength is inversely proportional to the temperature.

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4
Q

What is Stefan-Boltzmann’s Law?

A

The higher an object’s temperature, the more intensely the object emits electromagnetic radiation at all wavelengths and the shorter the wavelength at which it emits most strongly.

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5
Q

Formula for Wein’s Law.

A

Max wavelength = 0.0029 (Wein’s Constant) / Temperature

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6
Q

Stefan-Boltzmann Formula.

A

F = sigma * T^4

where F = energy flux measured in W m^-2
T = temperature in K
sigma = 5.67 * 10^-8 W m^-2K^-4

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7
Q

What is the temperature of the sun?

A

5800K

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8
Q

State Kirchhoff’s 1st Law.

A

A hot opaque body (blackbody) or dense gas, produces continuous spectrum

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9
Q

State Kirchhoff’s 2nd Law.

A

A hot, transparent gas produces an emission line spectrum.

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10
Q

State Kirchhoff’s 3rd Law.

A

A cool, transparent gas in front of a source of a continuous spectrum produces an absorption line spectrum.

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11
Q

What do we observe if a hot gas A is in front of an even hotter object or gas B?

A

The emission lines of A will darken the spectrum of B, we would see them as absorption lines.

NOTE: Gas in front must be cooler

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12
Q

Name for series of electron transistions from higher orbits to
(a) n = 1
(b) n = 2
(c) n = 3

A

(a) Lyman series (ultraviolet)
(b) Balmer series (visible)
(c) Paschen series (infrared)

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13
Q

Does the wavelength increase by the doppler effect when moving toward or away.

A

away.

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14
Q

In red-shift is wavelength of light increasing or decreasing.

A

Increasing.

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15
Q

Which is hotter a blue or red flame?

A

blue

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16
Q

If I have the brightness across the EM spectrum what can I get?

A

Temperature (SB law)

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17
Q

If a cloud of gas at 5000K is located between us and a red star (3000K) what will we on Earth observe.

(a) if the cloud is transparent
(b) the cloud is not transparent

A

(a) We will see the star’s continuous spectrum
(b) We will see emission lines from the gas and nothing from the star.

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18
Q

What can the spectral lines of a star tell us?

A

What the star is made of and how much of an element there is in the star.

19
Q

T or F. The hydrogen atom shows multiple emission and absorption lines.

A

True.

20
Q

T or F. When a star moves toward us only emission lines move to bluer wavelengths.

A

False.

Also absorption.

21
Q

Explain cosmological redshift.

A

If we know the velocity at which the universe expands we can know the distance of stars by their redshift spectra.

22
Q

What parts of the electromagentic spectrum can we most observe from Earth?

A

visible + radiowaves (most)

23
Q

Explain how a refractor telescope works.

A

A lens is used to bend the incoming light and focus it at one point. Convex lens converges on focus.

Short eyepiece lens than magnifies the image for easier viewing.

24
Q

What is chromatic aberration? Solution?

A

Problem with refractor telescopes that different colours do not focus at the same point.

Multiple Lenses

25
Q

Apart from chomatic aberration what other problems with refractor telescopes?

A
  1. Glass totally free of defects expensive
  2. Glass blocks ultraviolet
  3. Large lenses impossible
  4. A large lens distorts under its own weight.
26
Q

Example refractor telescope.

A

The big refractor at Yerkes Observatory.

27
Q

Explain reflector telescope.

A

A concave parabolic mirror is used to reflect the incoming light and focus it in one point. A Standard mirror is then used to reflect this image into an eyepiece.

28
Q

Explain difference between Newtonian and Cassegrain design.

A

Newtonian sends light downward
Cassegrain sends light through gap in parabolic mirror.

29
Q

Why is a parabolic mirror and not a spherical mirror used?

A

Parabolic mirror avoids spherical aberration.

30
Q

What is coma?

A

Star images far from the centre of field of view are elongated looking like teardrops by parabolic mirrors.

31
Q

Give an example of a reflector telescope.

A

Grantecan.

32
Q

Name the three properties of telescopes.

A
  • Light Gathering Power
  • Magnifying Power
  • Angular Resolution
33
Q

Formula for light gathering power.

A

L is proportional to the Area.
or
L is proportional to r^2

34
Q

Magnification formula.

A

M = focal length of objective / focal length of eyepiece

ratio of object’s angular diameter in telescope to naked eye angular diameter.

35
Q

Why is really high magnification not always good?

A

When magnification gets too high, objects become dim and lose contrast.

36
Q

Why is diffraction a problem with telescopes?

A

The small areas may lead to diffraction so light waves with small angular separation may appear to come from a single source.

37
Q

Formula for angular resolution. What is it?

A

A = 2.5 * 10^5 * lambda / D

A = arcsecs (smaller the better)
lambda = wavelength in meters
D = diameter in meters

Ability to distinguish between objects close to each other.

38
Q

Why are X-ray telescopes ineffective?

A

Despite very low wavelength, the high energy light cannot be focused using traditional methods so spatial resolution is poorer than optical.

39
Q

T or F. Reflector telescopes are light-weight telescopes easy to build at large scale.

A

True.

40
Q

T or F. In all situations and configurations, a bigger telescope observing the same light as a smaller one has a better angular resolution.

A

False.

41
Q

T or F. By the definition of the angular resolution, radio telescopes always have worse spatial resolution than optical telescopes.

A

False.

42
Q

What is the primary purpose of the objective of a telescope?

A

Gather light

43
Q

How to convert angstroms to meters?

A

1angstrom = 1×10^−10 meters

44
Q

One advantage of the Hubble Space telescope over ground based ones is what?

A

In orbit, it can operate close to its diffraction limit at visible wavelengths. No distortion caused by atmosphere.

Astronomy And Space Science (8 decks)

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