Astronomy 1010 - Chapter #5

redshift

A Doppler shift in which spectral features are shifted to longer wavelengths, observed when an object is moving away from the observer. These lines have positive velocities.

blueshift

A Doppler shift in which spectral features are shifted to shorter wavelengths, observed when an object is moving toward the observer. These lines have negative velocities.

emission

A _____ spectra is created when a continuous source of radiation passes through thin, cool gas; after absorbing some of this energy, de-exciting electrons release it in the form of a photon that creates "spikes" in the spectra.

absorption

A _____ spectra is created when a continuous source of radiation passes through thin, cool gas; electrons within absorb some of those photons and create "cut-outs" in the spectra.

continuous

A ______ spectrum appears as a single, smooth curve with a defined peak.

electric

A _______ field accelerates all charged particles.

magnetic

A _______ field accelerates and changes the direction of moving matter.

absorption

A _______ spectrum appears as a flat line with occasional downward-facing spikes.

emission

A _______ spectrum appears as a flat line with occasional upward-facing peaks.

gravitational

A ________ field accelerates all matter.

continuous

A blackbody or thermal spectrum is a ________ spectrum.

blackbody

A hypothetical object that serves as both a perfect absorber and a perfect emitter.

Unified Field Theory

A theory that seeks to describe all fundamental forces and the relationships between elementary particles in terms of a single mathematical framework. Not tested or proven.

Doppler effect

An observed change in the wavelength or frequency of a wave based on the motion of the emitting object.

increases

As you increase the temperature of a blackbody, the flux _____.

Stars can be equated with blackbodies, so according to Wien's Law, stars of different colors have different surface temperatures.

HW Question: A favorite object for amateur astronomers is the double star Albireo, with one of its components a golden yellow and the other a bright blue. What do these colors tell you about the relative temperatures of the two stars?

Equation: L = Area x Flux F = σ(T^4) = (5.67 x 10^-8) x (500^4) = 3.5 x 10^3 J/(m^2s) L = F x 1 = 3.5 x 10^3 J/s

HW Question: A panel with an area of one square meter is heated to a temperature of 500 K. How many watts is it radiating into its surroundings?

Equation: T = 279 (1 - a)0.25 / d0.5 a. a = .1 T = (279 ((1 - 0.1)^0.25)) / (1^0.5) = 272 K b. a = .9 T = (279 ((1 - 0.9)^0.25)) / (1^0.5) = 157 K

HW Question: A planet with no atmosphere at 1 AU from the Sun would have an average blackbody surface temperature of 279 K if it absorbed all the Sun's electromagnetic energy falling on it (albedo = 0). a. What would be the average temperature on this planet if its albedo were 0.1, typical of a rock-covered surface? b. What would be the average temperature if its albedo were 0.9, typical of a snow-covered surface?

Light is both a particle and a wave; at the atomic and subatomic level, these properties can co-exist.

HW Question: Is light a particle or a wave?

We can study emission and absorption lines in the laboratory here on Earth. When we see the exact same phenomena in far away objects, it supports the claims that physics is the same over enormous distances and allows us to assume the same physical laws we study on here Earth apply to the whole universe.

HW Question: Patterns of emission or absorption lines in spectra can uniquely identify individual atomic elements. Explain how positive identification of atomic elements can be used as one way of testing the validity of the cosmological principles discussed in Chapter #1.

Equation: λmax = 0.0029 / T λmax = 0.0029 / 100,000 = 2.9 x 10^-8 m. This is ultraviolet light.

HW Question: Some of the hottest stars known have a blackbody temperature of 100,000 K. What is the peak wavelength of their radiation? What type of radiation is this?

These lines allow us to identify the atoms and molecules producing them; studying these combination of lines allows us to determine the temperature, density, pressure, and ionization state, as well as the speed and direction of motion, of the material that created them.

HW Question: Spectra of astronomical objects show both bright and dark lines. Describe what these lines indicate about the atoms responsible for spectral lines.

Equation: L = Surface Area x Flux F = σ(T^4) = (5.67 x 10^-8) x (5780^4) = 6.33 x 10^7 J/( m^2s) SA = 4πR^2 = 4π (6.96 x 10^8)^2 = 6.09 x 10^18 m^2 L = F x SA = 3.85 x 10^26 J/s.

HW Question: The Sun has a radius of 6.96e5 km and a blackbody temperature of 5780 K. Calculate the Sun's luminosity.

Equation: T = (279 ((1 - a)^0.25)) / (d^0.5) T = (279 ((1 - 0.8)^0.25)) / ((97.7)^0.5) = 19 K

HW Question: The orbit of Eris, a dward planet, carries it out to a maximum distance of 97.7 AU from the Sun. Assuming an albedo of 0.8, what is the average temperature of Eris when it is farthest from the Sun?

Star #1 and Star #2 have the same apparent brightness and thus flux, meaning that L1/(d1)^2 = L2=(d2)^2. Since Star #2 is three times more distant, d2 = 3d1. Therefore, L1 /(d1)^2 = L2 /(3d1)^2 = L1 = L2 /9. Star #2 is nine times more luminous than Star #1.

HW Question: Two stars appear to have the same brightness, but one tar is 3 times more distance than the other. How much more luminous is the more distant star?

Evolutionary theory predicts that our eyes and those of most animals have evolved to be most sensitive to the bulk of light emanating from our nearby star, the Sun.

HW Question: Why is it not surprising that sunlight peaks in the visible?

a. Equation: λmax = 0.0029 / T 37 C = 310 K λmax = 0.0029 / 310 = 9.4 x 10^-6 m. b. Equation: L = FA F = σ(T^4) = (5.67 x 10^-8) x (310^4)= 524 J/(m^2s) L = F x .25 = 131 J/s.

HW Question: Your body, at a temperature of 37 degrees Celsius, emits radiation in the infrared region of the spectrum. a. What is the peak wavelength, in microns, of your emitted radiation? b. Assuming an exposed body surface area of .25 m^2, how many watts of power do you radiate?

Equation: λ = c/f (3 x 10^8 m/s) / (2.45 x 10^9 m/s) = 0.122 m = 12.2 cm

HW Question: Your microwave oven cooks by vibrating water molecules at a frequency of 2.45 gigahertz, or 2.45e9 Hz. What is the wavelength, in centimeters, of the microwave's electromagnetic radiation?

gas

Hot, dense ____ serves as a excellent model for a blackbody.

one; zero

If the albedo of an object is equal to ___, it has total reflection and is a perfect mirror; if the albedo is ____, it has total absorption and is a blackbody.

energy; Planck's constant

In the equation E = hf = hc/λ, E stands for _____ and h stands for _____.

wavelength; speed of light; frequency

In the equation λ = c/f, λ stands for _____, c stands for ______, and f stands for ______.

both

Is light a wave or a particle?

excites

Light ____ the electrons in an atom, giving them the energy to spring upwards through the orbitals.

particle behavior

The _____ ______ of light is proven by the photoelectric effect.

albedo

The ______ is the measure of how well a surface reflects solar energy.

temperature

The ________ of a planet can be determined with the equation: (279 ((1-a)^1/4))/(d^1/2), where a is albedo and d is distance measured in AU.

diffraction

The bending of a light wave as it moves around an obstacle or passes through a narrow opening.

refraction

The bending of a light wave as it passes at an angle from one medium to another.

spectra (spectrum)

The distribution of light as a function of wavelength, frequency, or energy is called _______.

luminosity

The equation for _____ is 4π(R^2)F, where F is flux, or FA.

flux

The equation for _____, also known as the Stefan-Boltzmann formula, is σ(T^4), where σ = 5.67 x 10^-8 J/sm^2k^4.

photosphere

The inner layer of the sun's atmosphere, surrounded by the solar atmosphere.

interference

The interaction between two light waves that meet. If two crests or two troughs of the wavelength meet, they amplify; if a crest and a trough meet, they cancel out.

photon

The particle manifestation of light is called a ______.

spectroscopy

The study of the properties of light that depend on wavelength; through this study, one can determine the composition, temperature, density, pressure, and speed of his or her subject.

continuous, absorption, emission

The three types of spectrum are _______, ________, and _______.

field

The wave manifestation of light is an oscillating electric and magnetic ______.

Wien's Law

This law states that objects at different temperatures emit spectra that peak at different wavelengths; for example, two stars of differing colors will have different surface temperatures.

Wien's Law

This law states that λmax = .0029/T, where λ is measured in meters and T in Kelvin.

wave behavior

Three examples of the ____ _______ of light are refraction, diffraction, and interference.

blackbodies

When determining the temperature of planets, we assume that they are _________.

flux

_____ is the energy per second per area, or energy emitted, of an object.

quantum state

______ _____ states that an electron has a certain amount of energy and requires a specific amount more to jump between orbitals in an atom.

luminosity; flux

______ refers to brightness; ______ refers to energy emitted or apparent brightness.

luminosity

_______ is the energy output per second, or brightness, of an object.