The Cosmic Perspective Ch 14-15

What is the Sun composed of?

-Sun is giant ball of plasma

-Composed mostly of hydrogen, a large portion of helium and other trace elements

How do we find the distance from the Earth to Sun and the size of the Sun?

-The Sun's mass can be measured using Newton's version of Kepler's 3rd law, mass is about 2x10^30 kg

-Using Sun's angular size and distance, radius is 700,000km

-Parallax can be used to measure distance

What causes the Sun to shine?

-Sun converts mass into energy through nuclear fusion

-Gravitational contraction, process where Sun generates energy by slowly contracting in size

-Combination of both, contraction heated Sun enough to start fusion

What is the proton-proton chain?

-hydrogen fusion reaction that transforms 4 individual protons into helium nucleus with 2 protons and 2 neutrons

Step 1 proton chain

-2 protons fuse to form nucleus of 1 proton, 1 neutron: hydrogen isotope

-proton converted into neutron, charge carried off by neutrino

Step 2 proton chain

-isotope nuclei collides and fuses with a proton

-nucleus of helium-3, 2 protons 1 neutron

Step 3 proton chain

-neutron added to helium-3, results in normal helium-4

-2 extra protons are carried off

What are fusion reactions?

-collisions or separation of atomic nuclei

-occurs in Sun's core because of high pressure and temperature

-w/out temp, collisions wouldn't be as hard

-w/out pressure, plasma would not exist

E=mc^2

-shows that mass itself contains an enormous amount of potential energy

-Sun's mass contains more than enough energy to account for billions of years

What is Coulomb's Law?

-inverse square law of physics that describes electrostatic interaction between electrically charged particles

-force of attraction or repulsion between 2 point charges is directly proportional to the product of magnitude of each charge and inversely proportional to the square of distance between them

What is solar granulation and what causes it?

-Bubbling pattern visible in the photosphere of the Sun, produced by underlying convection

-Photosphere is covered with convection cells called granules, which have a very short lifespan

How does energy get from the core of the Sun to the Earth?

-Energy produced through fusion reflects off of photons in the radiation zone, then once it reaches the convection zone is carried upward by convection currents

-photosphere is not dense so it allows energy to escape in form of thermal radiation

What is a sunspot?

-Sunspots are dark blotches on the Sun's surface, caused by magnetic fields

-Darker because they are cooler than surrounding plasma, magnetic fields keep hot plasma from entering

What is the relation between magnetic field lines and sunspots?

-Sunspots are regions with strong magnetic fields, they occur where tightly wound magnetic fields poke nearly straight out of the solar interior

What is the sunspot cycle and how does the sun change with the cycle?

-the sunspot cycle is a cycle in which the average number of sunspots per year gradually rises and falls, 11 years between maximums (22 per cycle)

-prominences and CME most commonly occur at maximum

What is differential rotation? How is this related to the sunspot cycle?

-differential rotation where different parts rotate at different speeds, equator of Sun rotates quicker than poles

-this produces the contorted field lines that generate sunspots and other solar activity

What are prominences and coronal mass ejections?

-prominences occur when gas in the Sun's corona and chromosphere becomes trapped in loops of magnetic field lines arching above the Sun's surface

-CME's are huge bubbles that have strong magnetic fields and eject highly charged particles from the Sun's corona

How does the sunspot cycle affect us on the Earth?

-some data suggest connection between sunspot cycle and Earth's climate

-when solar activity virtually ceased, temperatures dropped very low

What are auroras?

-aurora borealis are the northern lights that are created by charged particles entering the atmosphere and colliding with the Earth's magnetic field

What is the inverse square law for light? (formula)

apparent brightness=luminosity/4Π x distance^2

What does the inverse square law for light demonstrate?

-relates apparent brightness, luminosity and distance of any light source

-amount of light received per unit area decrease with increasing distance by the square of distance

What is the magnitude scale and how does it function?

-magnitude system originally classified stars according to how bright they look to human eyes, now each difference of 5 magnitudes is defined to represent factor of exactly 100 times as bright

-1 highest

What is the difference between apparent magnitude and absolute magnitude?

-apparent magnitude compares how bright different stars appear in the sky

-absolute magnitude is a way to describe stellar luminosities, star's absolute magnitude is apparent magnitude it would have if it were 10 parsecs from Earth

How is stellar parallax used to measure the distances to the stars?

-stellar parallax is the annual shift in a star's apparent position caused by earth's orbit around Sun

-parallax angle is equal to half star's annual shift, distant stars have smaller parallax angles

Why does this system eventually break down?

-parallax only technique tells us stellar distance without assumptions of nature of stars

What is a parsec?

-parallax angle of 1 arcsecond is 1 parsec (pc)

-all stars have parallax angles smaller than 1 arcsecond, so farther than 1 parsec away

d (in parsecs)=1/p (in arcseconds)

What is the relationship between stellar parallax and distance?

D=1/p

-1 parsec is equivalent to 3.26 light years

-ex. distance to star with parallax angle of 1/2 arcsecond is 2 parsecs away

What is a spectral class and luminosity class of a star?

-spectral type is assigned to a star determined from spectral lines present in a stars spectrum, determined by surface temp, measured by OBAFGKM (hottest to coolest)

What is the H-R Diagram?

-diagram which gives a graphical representation of the different spectrum and luminosity of stars

How do you read it?

Horizontal axis is spectrum (how hot is it)

Vertical axis is luminosity (how bright)

Main group is called main sequence, top right corner is super giants, below them is giants, white dwarfs are in bottom left

What are binary stars?

Binary star systems are systems where 2 stars continually orbit one another, half of all stars orbit a companion star

What is a visual, spectroscopic and eclipsing binary?

-visual binary is a pair of stars that can be seen distinctly as they orbit one another

-eclipsing binary is a pair of stars that orbit plane of sight, sometimes we see both, sometimes one eclipses the other and brightness drops

-spectroscopic binary is when a star is periodically orbiting towards us and away from us, the type of light we get will vary

How are they used to find the masses of stars?

-Newton's version of Kepler's third law, when we observe one object orbiting another we have to measure both orbital period and average orbital distance of object

-in visual binary, observe how long orbit takes

-in eclipsing binary, time between eclipses

-spectroscopic binary, measure time between shift in spectral lines

What are stellar clusters? How do we determine the age of a cluster?

-stellar clusters are when many stars congregate in groups, they all formed at the same time and they are all about the same distance from Earth

-the age of the cluster is equal to the lifetimes of stars at its main-sequence turnoff point

What is the main-sequence turnoff point?

the point on a cluster's H-R Diagram where its stars turn off from the main sequence (they burn out)