Spectroscopy, Telescopes

Question 1

What is a blackbody?

Answer 1

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.

Question 2

What is blackbody radiation?

Answer 2

Refers to the light emitted by a blackbody.

Question 3

What is Wein’s Law?

Answer 3

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

Question 4

What is Stefan-Boltzmann’s Law?

Answer 4

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.

Question 5

Formula for Wein’s Law.

Answer 5

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

Question 6

Stefan-Boltzmann Formula.

Answer 6

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

Question 7

What is the temperature of the sun?

Answer 7

5800K

Question 8

State Kirchhoff’s 1st Law.

Answer 8

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

Question 9

State Kirchhoff’s 2nd Law.

Answer 9

A hot, transparent gas produces an emission line spectrum.

Question 10

State Kirchhoff’s 3rd Law.

Answer 10

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

Question 11

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

Answer 11

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

Question 12

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

Answer 12

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

Question 13

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

Answer 13

away.

Question 14

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

Answer 14

Increasing.

Question 15

Which is hotter a blue or red flame?

Answer 15

blue

Question 16

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

Answer 16

Temperature (SB law)

Question 17

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

Answer 17

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

Question 18

What can the spectral lines of a star tell us?

Answer 18

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

Question 19

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

Answer 19

True.

Question 20

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

Answer 20

False.

Also absorption.

Question 21

Explain cosmological redshift.

Answer 21

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

Question 22

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

Answer 22

visible + radiowaves (most)

Question 23

Explain how a refractor telescope works.

Answer 23

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.

Question 24

What is chromatic aberration? Solution?

Answer 24

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

Multiple Lenses

Question 25

Apart from chomatic aberration what other problems with refractor telescopes?

Answer 25

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

Question 26

Example refractor telescope.

Answer 26

The big refractor at Yerkes Observatory.

Question 27

Explain reflector telescope.

Answer 27

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.

Question 28

Explain difference between Newtonian and Cassegrain design.

Answer 28

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

Question 29

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

Answer 29

Parabolic mirror avoids spherical aberration.

Question 30

What is coma?

Answer 30

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

Question 31

Give an example of a reflector telescope.

Answer 31

Grantecan.

Question 32

Name the three properties of telescopes.

Answer 32

- Light Gathering Power - Magnifying Power - Angular Resolution

Question 33

Formula for light gathering power.

Answer 33

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

Question 34

Magnification formula.

Answer 34

M = focal length of objective / focal length of eyepiece ratio of object's angular diameter in telescope to naked eye angular diameter.

Question 35

Why is really high magnification not always good?

Answer 35

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

Question 36

Why is diffraction a problem with telescopes?

Answer 36

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

Question 37

Formula for angular resolution. What is it?

Answer 37

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.

Question 38

Why are X-ray telescopes ineffective?

Answer 38

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

Question 39

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

Answer 39

True.

Question 40

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

Answer 40

False.

Question 41

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

Answer 41

False.

Question 42

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

Answer 42

Gather light

Question 43

How to convert angstroms to meters?

Answer 43

1angstrom = 1×10^−10 meters

Question 44

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

Answer 44

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