Exam 3 Phys 202 (Chapter 17-23)

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Distinguish between luminosity and apparent brightness

Luminosity is the total energy a star emits per second while apparent brightness is how much of that energy reaches Earth depending on distance

How do astronomers use the magnitude system to describe apparent brightness

Smaller or more negative magnitudes mean brighter objects and a 5 magnitude difference equals 100 times brightness

Explain the relationship between a star's color and its temperature

Hotter stars appear blue while cooler stars appear red due to wavelength differences

What is a color index and what does it tell astronomers about a star

It is the difference between magnitudes in two filters and indicates a star’s temperature

What is the primary reason for differences in stellar spectra

Differences are mainly due to temperature affecting ionization and absorption lines

List the seven standard spectral classes from hottest to coolest

O B A F G K M

How can astronomers distinguish a giant star from a smaller star of the same temperature

Giants have lower pressure and narrower spectral lines

Define radial velocity and explain how it is measured

It is motion toward or away from us measured using Doppler shift

What is proper motion and how does it differ from radial velocity

Proper motion is motion across the sky while radial velocity is along the line of sight

How does line broadening reveal rotation

Rotation causes Doppler shifts across the star widening spectral lines

What is a selection effect in observing stars

Bright stars seen are often distant and luminous not nearby

Differentiate between visual and spectroscopic binaries

Visual binaries are directly seen while spectroscopic are detected via Doppler shifts

How is Newton’s version of Kepler’s third law used

Orbital period and distance give total mass of the system

How do astronomers measure stellar diameters

Using lunar occultations or eclipsing binaries

What are brown dwarfs

Objects not massive enough for sustained hydrogen fusion

State the mass luminosity relation

Luminosity is proportional to mass to the fourth power

What is plotted on an H-R diagram

Luminosity vs temperature

Describe the main sequence

Stars fusing hydrogen arranged by mass

Where are white dwarfs on the H-R diagram

Lower left hot but dim

What does 90 percent of stars on main sequence imply

Stars spend most of life there

How far away is a star with parallax 0.2 arcsec

5 parsecs

Distance to M31 technique

Period luminosity relation for Cepheid variables

Why wasn’t parallax measured until 1838

Shift too small to see

Hotter interstellar clouds have what property

Lower density

How do fragile molecules survive in space

Dense clouds with dust

Why is some gas millions of degrees

Shock waves from exploding stars

Which property requires distance to determine

Its luminosity

Baseline used for parallax

Half the diameter of Earth’s orbit

Why don’t some spectral lines shift in binaries

Lines come from interstellar matter

Dust in interstellar clouds consists of what

Tiny solid grains

How has the meter evolved

Defined now by distance light travels in a fraction of a second

What is triangulation and its limitation

Uses angles and baseline but limited by tiny parallax shifts

What is stellar parallax

Apparent shift used to measure distance

Define AU light year and parsec

AU Earth Sun distance light year distance light travels parsec equals 3.26 light years

How is radar used for distance

Measures roundtrip time of radio waves

What are variable stars

Stars whose brightness changes used for distance

What is the Cepheid period luminosity relation

Longer period means higher luminosity

How do RR Lyrae stars differ

Same luminosity useful within galaxy

How is spectroscopic parallax used

Spectrum gives luminosity then distance

What is the cosmic distance ladder

Series of methods to measure distances

What is the ISM composed of

Mostly gas with some dust

How do H II regions form

UV light ionizes hydrogen causing red glow

How is neutral hydrogen detected

21 cm radio line

What is interstellar reddening

Dust scatters blue light making stars appear redder

What are cosmic rays

High speed nuclei from supernova shocks

Why are molecules common in dark clouds

Dense cold dust shields radiation

What is the baryon cycle

Matter cycles between stars and ISM

How do dust grains help molecules form

Provide surfaces for reactions

What is the Local Hot Bubble

Hot low density region around Sun

Why use infrared or radio astronomy

Dust is transparent to longer wavelengths

What determines a star’s position on the main sequence

Its mass

How was the first exoplanet detected

Doppler shift method

Where is Proxima Centauri’s habitable zone

Closer to the star

What is the Orion Nebula

Cloud of gas and dust lit by new stars

What mission found many planets

Kepler mission

Why couldn’t Kepler detect very small planets

Dips too small

Hotter star same luminosity moves where on H-R diagram

To the left

What surprised astronomers about first exoplanet

4 day orbit close to star

What shows planets forming in disks

Empty dust lanes

What defines habitable zone planets

Liquid water possible

What starts protostar formation

Collapse of dense cold cloud cores

Why is H-R diagram important for protostars

Tracks temperature and luminosity changes

Why are exoplanets hard to observe directly

Star glare overwhelms them

How does Doppler method detect planets

Measures star wobble

What does transit method provide

Planet size and period

What are hot Jupiters

Massive planets close to stars

What are super Earths and mini Neptunes

Common planets unlike our system

What shows planet formation in disks

Donut shaped gaps

What is triggered star formation

Compression by massive stars

What did Kepler 444 show

Rocky planets formed early

What indicates cluster age on H-R diagram

Main sequence turnoff point

What causes star to expand into giant

Hydrogen in core used up

Why do massive stars differ

Fuse beyond carbon oxygen

Why can’t Sun like stars fuse heavier elements

Not hot enough

Why does hydrogen shell fusion begin

Core collapse heats outer layer

Which cluster has oldest stars

Globular cluster

Where are globular clusters found

Spherical halo

Where are heavy elements produced

Massive stars

First generation stars composition

Little or no heavy elements

Which stars live longest

K

What is zero age main sequence

Start of hydrogen fusion

Why do massive stars have short lifetimes

Burn fuel faster

What happens when hydrogen is exhausted

Core contracts and shell fusion begins

How do outer layers respond

Expand and cool

Why are clusters useful

Same age different masses

Difference between globular and open clusters

Old halo vs young disk

What is main sequence turnoff

Point stars leave sequence

What is triple alpha process

Helium fuses into carbon

What are planetary nebulae

Ejected shells of dying stars

How does nucleosynthesis differ in massive stars

Can form elements up to iron

White dwarf vs main sequence same mass

Smaller in diameter