Spectroscopy, Telescopes Flashcards
What is a blackbody?
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.
What is blackbody radiation?
Refers to the light emitted by a blackbody.
What is Wein’s Law?
The blackbody radiation consists of a continuous spectrum that peaks at a certain wavelength. This wavelength is inversely proportional to the temperature.
What is Stefan-Boltzmann’s Law?
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.
Formula for Wein’s Law.
Max wavelength = 0.0029 (Wein’s Constant) / Temperature
Stefan-Boltzmann Formula.
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
What is the temperature of the sun?
5800K
State Kirchhoff’s 1st Law.
A hot opaque body (blackbody) or dense gas, produces continuous spectrum
State Kirchhoff’s 2nd Law.
A hot, transparent gas produces an emission line spectrum.
State Kirchhoff’s 3rd Law.
A cool, transparent gas in front of a source of a continuous spectrum produces an absorption line spectrum.
What do we observe if a hot gas A is in front of an even hotter object or gas B?
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
Name for series of electron transistions from higher orbits to
(a) n = 1
(b) n = 2
(c) n = 3
(a) Lyman series (ultraviolet)
(b) Balmer series (visible)
(c) Paschen series (infrared)
Does the wavelength increase by the doppler effect when moving toward or away.
away.
In red-shift is wavelength of light increasing or decreasing.
Increasing.
Which is hotter a blue or red flame?
blue
If I have the brightness across the EM spectrum what can I get?
Temperature (SB law)
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) We will see the star’s continuous spectrum
(b) We will see emission lines from the gas and nothing from the star.
What can the spectral lines of a star tell us?
What the star is made of and how much of an element there is in the star.
T or F. The hydrogen atom shows multiple emission and absorption lines.
True.
T or F. When a star moves toward us only emission lines move to bluer wavelengths.
False.
Also absorption.
Explain cosmological redshift.
If we know the velocity at which the universe expands we can know the distance of stars by their redshift spectra.
What parts of the electromagentic spectrum can we most observe from Earth?
visible + radiowaves (most)
Explain how a refractor telescope works.
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.
What is chromatic aberration? Solution?
Problem with refractor telescopes that different colours do not focus at the same point.
Multiple Lenses
Apart from chomatic aberration what other problems with refractor telescopes?
- Glass totally free of defects expensive
- Glass blocks ultraviolet
- Large lenses impossible
- A large lens distorts under its own weight.
Example refractor telescope.
The big refractor at Yerkes Observatory.
Explain reflector telescope.
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.
Explain difference between Newtonian and Cassegrain design.
Newtonian sends light downward
Cassegrain sends light through gap in parabolic mirror.
Why is a parabolic mirror and not a spherical mirror used?
Parabolic mirror avoids spherical aberration.
What is coma?
Star images far from the centre of field of view are elongated looking like teardrops by parabolic mirrors.
Give an example of a reflector telescope.
Grantecan.
Name the three properties of telescopes.
- Light Gathering Power
- Magnifying Power
- Angular Resolution
Formula for light gathering power.
L is proportional to the Area.
or
L is proportional to r^2
Magnification formula.
M = focal length of objective / focal length of eyepiece
ratio of object’s angular diameter in telescope to naked eye angular diameter.
Why is really high magnification not always good?
When magnification gets too high, objects become dim and lose contrast.
Why is diffraction a problem with telescopes?
The small areas may lead to diffraction so light waves with small angular separation may appear to come from a single source.
Formula for angular resolution. What is it?
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.
Why are X-ray telescopes ineffective?
Despite very low wavelength, the high energy light cannot be focused using traditional methods so spatial resolution is poorer than optical.
T or F. Reflector telescopes are light-weight telescopes easy to build at large scale.
True.
T or F. In all situations and configurations, a bigger telescope observing the same light as a smaller one has a better angular resolution.
False.
T or F. By the definition of the angular resolution, radio telescopes always have worse spatial resolution than optical telescopes.
False.
What is the primary purpose of the objective of a telescope?
Gather light
How to convert angstroms to meters?
1angstrom = 1×10^−10 meters
One advantage of the Hubble Space telescope over ground based ones is what?
In orbit, it can operate close to its diffraction limit at visible wavelengths. No distortion caused by atmosphere.
