REMINDERS Exam II next Thursday, April 14! Practice exam posted on website - Same format as first exam – Multiple Choice & Short Answer Review session

REMINDERS

• Exam II next Thursday, April 14!

• Practice exam posted on website - Same format as first exam –

Multiple Choice & Short Answer

• Review session (Q & A only) Tuesday, April 12 @ 7 pm

Location: normal lecture hall in Physics

REMINDERS






REMINDERS






Discussion REVIEW plan

• 1 Chapters covered

• 2 Main equations to know

• 3 Brief overview & summary

• 4 Sample discussion questions

• 5 Sample multiple choice

Material Covered

• Chapter 5 – Light, interaction with matter, telescopes

• Chapter 10 – The Sun • Chapter 11 – Stars – overview / properties• Chapter 12 – Stellar evolution• Chapter 13 – Deaths of stars

• Textbook, lecture notes, discussion section activities!

Important Relations

E = hc / λ = h * frequencyphoton

T ~ 1 / λ peak

distance = 1 / parallax

L = 4 π r σ T ~ r T 2 24 4

Brightness or Flux ~ 1 / (distance)2

L ~ M3

Key things to Memorize:

• Equations already mentioned• EM spectrum• HR diagram (most time on main sequence)• Life cycle of a low & high mass stars• Stellar Cutoffs – 8 M, 2 M, 1.4 M, 3 M• Types of spectra & how they are formed• Structure of our SUN• What makes the sun shine? Evidence for nuclear fusion

in the core.• H fusion – (4 H → 1 He + energy + neutrinos)• Spectral Sequence, luminosity class - OBAFGKM

Key Concepts:

• Longer wavelength photon → lower E

• Shorter wavelength photon → higher E

• Hydrostatic Equilibrium– Radiation pressure, degeneracy pressure

(electron and neutron) vs. gravity

• Doppler Effect

• Distance determination – distance modulus, parallax

Key Concepts (continued):• Bohr atomic model – explaining

absorption/emission through electron transitions

• Telescopes improve with collecting area and angular resolution

• Positive nuclei repel, so high T required in stellar cores for fusion of heavier and heavier elements

• Solar thermostat

• Main sequence is a sequence of MASS

Essay topics may include:

• Describe the evolution of a low mass/high mass star

• Draw and label an HR diagram

• Emission/Absorption/Continuous spectra – Describe how each is produced

• Newton’s form of Kepler’s 3rd law – calculating stellar masses

• Binary star systems

Essay topics may include:

• Inverse square law (Flux vs. Luminosity)• Doppler shift• Describe Heliocentric Parallax and discuss

the limits of this method• Why do we put telescopes into space?• Why does the sun shine?• What is the sun’s structure?

Other stuff to emphasize:

Know GENERAL idea ONLY:

Concept Overview & Summary

The electromagnetic spectrumFigure 3.5

Identify the following portions of theElectromagnetic spectrum:

A B D EC

The electromagnetic spectrumFigure 3.5

Which end of the spectrum is more energetic, A or B? Why?

A B

Gamma raysX-raysUltravioletVisibleInfraredMicrowavesRadio

SHORT Wavelength ( λ ) HI Frequency ( ν or f )

LONG Wavelength ( λ ) LOW Frequency ( ν or f )

These two pictures describe what?

“photon”wave

&

Light has a DUAL NATURE!

“photon”wave

&

Energy of photon = (Planck’s constant) x (frequency) or (c / λ)

If the Hydrogen

gas cloud is moving towards

Earth, the absorption line marked will shift in

which direction?

BA

An absorption line of Hydrogen measured at rest

How do light and matter interact?KNOW THESE DEFINITIONS!

• Emission

• Absorption

• Transmission

• Reflection or Scattering

Electromagnetic radiationFigure 3.8What does this diagram illustrate?

What types of light spectra can we observe?

1. Continuous spectra

2. Absorption spectra

3. Emission spectra

Which is the absorption spectra?

Which is the continuous spectra?

Which is the emission spectra?

BLUE

Yellow

RED

BLACK

Which spectrum is coming from the coolest object?

BLUE

Yellow

RED

BLACK

At what wavelength does the peak of the yellowspectrum lie? What type of star might this be?

BLUE

Yellow

RED

BLACK

Is the star producing the yellow or red spectrum hotter? Why?

BLUE

Yellow

RED

BLACK

Which spectrum is coming from the hottest object?

Which star is more luminous?

T = 15,000 KRadius = 1 unit T = 15,000 K

Radius = 2 units


T = 3,000 KRadius = 1 unit



T = 3,000 KRadius = 7 units


REMEMBER!

Luminosity of a star is intrinsic.

Depends on Temperature & Radius.

L ~ R T 2 4

For which stars would we observe a Doppler Shift?

A

B

C

Doppler shiftFigure 3.18

Doppler Effect Summary

Motion toward or away from an observer causes a

shift in the observed wavelength of light:

• blueshift (shorter wavelength)

motion _______ you

• redshift (longer wavelength) motion AWAY

from you

• greater shift greater speed

Doppler Effect Summary

Motion toward or away from an observer causes a

shift in the observed wavelength of light:

• blueshift (shorter wavelength) motion toward

you

• redshift (longer wavelength)

motion ______ from you

• greater shift greater speed

How do telescopes help us learn about the universe?

• Telescopes collect more light than our eyes light-collecting area

• Telescopes can see more detail than our eyes angular resolution

• Telescopes/instruments can detect light that is invisible to our eyes (e.g., infrared, ultraviolet)

Angular Resolution

• The minimum angular separation that the telescope can distinguish.

What is this diagram illustrating?

Why can parallax only be used for nearby stars?

Are the emission lines locatedin the UV part of the spectrum or

the IR part of the spectrum?

Is it on FIRE?

Which is the correct explanation for the sun’s shining?

Is it CONTRACTING?

Is it powered by NUCLEAR ENERGY?

E = mc?

- Einstein, 1905

In Einstein’s famous equation, what should the exponent be?

This means that a ‘lil bit of mass can be converted to a LOT of energy

The balance of the inward force of gravity with the outward force of pressure due to radiation is referred to as ?

Solar wind

A) Corona

B) ChromosphereC) Photosphere

D) Core

Give the approximateTemperatures of eachOf these layers.

What enables nuclei to overcome repulsion and get close enough to fuse in the core of a star?

Sun releases energy by fusing four hydrogen nuclei into what?

?

IN4 protons

OUT4He nucleus2 positrons

2 gamma rays2 _______????

What else results besides a He

nucleus?

Total mass is 0.7% lower

Solar Thermostat

Temperature Restored

Temperature Decreases

Fusion Rate (Increases or Decreases)?

Core (compresses or expands)?

How does the energy from fusion get out of the Sun?

Why do sunspots appear dark on the surface of the sun?

Number of sunspots rises and falls in cycle of ________ years.

A difference between an ultraviolet photon and a radio photon is that

• A. the energy of the radio photon is

greater

• B. only the radio photon is an

electromagnetic wave

• C. only the ultraviolet photon is an


• D. the energy of the ultraviolet photon is greater

• E. none of the answers are correct

A difference between an ultraviolet photon and a radio photon is that

• A. the energy of the radio photon is

greater

• B. only the radio photon is an


• C. only the ultraviolet photon is an


• D. the energy of the ultraviolet photon is greater

• E. none of the answers are correct

The speed of a radio wave is

• A. the speed of sound

• B. slower than the speed of light

• C. slower than the speed of sound

• D. the speed of light

• E. none of the above

The speed of a radio wave is

• A. the speed of sound

• B. slower than the speed of light

• C. slower than the speed of sound

• D. the speed of light

• E. none of the above

The sun

• A. is composed of ionized gas that is mostly

neon

• B. is composed of molecular gas that is mostly

neon

• C. is composed of ionized gas that is mostly

hydrogen

• D. is composed of molecular gas that is

mostly hydrogen

The sun

• A. is composed of ionized gas that is mostly

neon

• B. is composed of molecular gas that is mostly

neon

• C. is composed of ionized gas that is mostly

hydrogen

• D. is composed of molecular gas that is

mostly hydrogen

The energy source for the sun is

• A. combustion of hydrocarbons

• B. solar flares

• C. nuclear fission, the splitting of two

hydrogen atoms

• D. nuclear fusion, the joining of two

hydrogen atoms

• E. combustion of hydrogen

The energy source for the sun is

• A. combustion of hydrocarbons

• B. solar flares

• C. nuclear fission, the splitting of two

hydrogen atoms

• D. nuclear fusion, the joining of two

hydrogen atoms

• E. combustion of hydrogen

The layer of the sun that emits most of the light we see is

• A. the corona

• B. the chromosphere

• C. the photosphere

• D. none of the answers are correct

The layer of the sun that emits most of the light we see is

• A. the corona

• B. the chromosphere

• C. the photosphere

• D. none of the answers are correct

Electromagnetic radiation from astronomical objects can be studied from the surface of the Earth in which part of

the spectrum?

• A. gamma-rays

• B. x-rays

• C. radio

Electromagnetic radiation from astronomical objects can be studied from the surface of the Earth in which part of

the spectrum?

• A. gamma-rays

• B. x-rays

• C. radio

The hotter an object

• A. the brighter it appears at all wavelengths, and the longer the wavelength at which it appears brightest• B. the shorter the wavelength at which it appears brightest• C. The brighter it appears at all wavelengths, and the shorter the wavelength at which it appears brightest• D. the longer the wavelength at which it appears brightest• E. the brighter it appears at all wavelengths

The hotter an object

• A. the brighter it appears at all wavelengths, and the longer the wavelength at which it appears brightest• B. the shorter the wavelength at which it appears brightest• C. The brighter it appears at all wavelengths, and the shorter the wavelength at which it appears brightest• D. the longer the wavelength at which it appears brightest• E. the brighter it appears at all wavelengths

Heat affects wavelength Figure 3.6

An object emits an emission line spectrum. If the object moves towards

an observer,• A. the observed emission lines shift to

shorter wavelengths

• B. the observed emission lines shift to longer

wavelengths

• C. the emission line spectrum shifts to a

continuous spectrum

• D. the emission line spectrum shifts to

an absorption line spectrum

An object emits an emission line spectrum. If the object moves towards

an observer,• A. the observed emission lines shift to

shorter wavelengths

• B. the observed emission lines shift to longer

wavelengths

• C. the emission line spectrum shifts to a

continuous spectrum

• D. the emission line spectrum shifts to

an absorption line spectrum

The hottest part of the solar atmosphere

• A. found in sunspots

• B. is the photosphere

• C. is the corona

• D. is the chromosphere

The hottest part of the solar atmosphere

• A. found in sunspots

• B. is the photosphere

• C. is the corona

• D. is the chromosphere

Which of the following is ordered by increasing wavelength?

• A. infrared, visible, radio, gamma-ray

• B. visible, infrared, radio, gamma-ray

• C. gamma-ray, visible, infrared, radio

• D. radio, visible, infrared, gamma-ray

Which of the following is ordered by increasing wavelength?

• A. infrared, visible, radio, gamma-ray

• B. visible, infrared, radio, gamma-ray

• C. gamma-ray, visible, infrared, radio

• D. radio, visible, infrared, gamma-ray

An atom is ionized if

• A. it has lost a proton

• B. it has lost an electron

• C. it has lost a neutron

• D. it has absorbed a photon

An atom is ionized if

• A. it has lost a proton

• B. it has lost an electron

• C. it has lost a neutron

• D. it has absorbed a photon

Sunspots appear darker than the surrounding photosphere because

• A. they have a carbonaceous composition

• B. they have an icy composition

• C. they are cooler than their surroundings

• D. they are shadowed from coronal

radiation

Sunspots appear darker than the surrounding photosphere because

• A. they have a carbonaceous composition

• B. they have an icy composition

• C. they are cooler than their surroundings

• D. they are shadowed from coronal

radiation

High mass stars have shorter lifetimes than low mass stars because high mass

stars• A. have luminosities that are far larger than low

mass stars

• B. have less hydrogen than low mass stars

• C. have less helium than low mass stars

• D. release less energy per nuclear reaction

than low mass stars

High mass stars have shorter lifetimes than low mass stars because high mass

stars• A. have luminosities that are far larger than low

mass stars

• B. have less hydrogen than low mass stars

• C. have less helium than low mass stars

• D. release less energy per nuclear reaction

than low mass stars

If the Sun were replaced by a black hole of the same mass,

• A. a great sucking sound would be heard

• B. the Earth would continue to orbit pretty much

as it does now

• C. the Earth would fall directly towards the

black hole

• D. the Earth would spiral into the black hole

over the next 1000 years

If the Sun were replaced by a black hole of the same mass,

• A. a great sucking sound would be heard

• B. the Earth would continue to orbit pretty much

as it does now

• C. the Earth would fall directly towards the

black hole

• D. the Earth would spiral into the black hole

over the next 1000 years

The most common stars are

• A. lower main sequence stars

• B. supergiants

• C. giants

• D. upper main sequence stars

• E. neutron stars

The most common stars are

• A. lower main sequence stars

• B. supergiants

• C. giants

• D. upper main sequence stars

• E. neutron stars

Main sequence stars

• A. are stars which have no hydrogen or

helium

• B. have nuclear fusion of hydrogen

occurring in their cores

• C. are stars which are mostly made of

hydrogen

• D. are stars found in spiral arms

Main sequence stars

• A. are stars which have no hydrogen or

helium

• B. have nuclear fusion of hydrogen

occurring in their cores

• C. are stars which are mostly made of

hydrogen

• D. are stars found in spiral arms

A planetary nebula is

• A. produced by a supernova explosion

• B. a nebula within which planets are

forming

• C. the expelled outer envelope of a

medium mass star

• D. a cloud of hot gas surrounding a planet

A planetary nebula is

• A. produced by a supernova explosion

• B. a nebula within which planets are

forming

• C. the expelled outer envelope of a

medium mass star

• D. a cloud of hot gas surrounding a planet

The density of a __________ is greater than the density of a ___________.

• A. neutron star, black hole

• B. pulsar, neutron star

• C. pulsar, white dwarf

• D. white dwarf, pulsar

• E. white dwarf, black hole

The density of a __________ is greater than the density of a ___________.

• A. neutron star, black hole

• B. pulsar, neutron star

• C. pulsar, white dwarf

• D. white dwarf, pulsar

• E. white dwarf, black hole

Documents

REMINDERS Exam II next Thursday, April 14! Practice exam posted on website - Same format as first exam – Multiple Choice & Short Answer Review session