Astronomy Ch 15 Lec 9/10

Front 1

What are the steps in measuring a stars brightness?

Back 1

luminosity is the total amount of power a star radiate into space per second.
The apparent brightness is the amount of starlight that reaches earth.

to get brightness we must divide luminosity by area of the sphere (4pi[radius]squared)

Front 2

How is the relationship betwen apparent brightness and luminosity determined?

Back 2

it is determined based on distance. brightness is equal to the luminosity (energy per second emitted) times the area of the sphere (4pi times distance squared)

we must first measure a stars distance and apparent brightness to achieve a measurement of luminosity.

Front 3

What is a paralax?

Back 3

paralax is a term to describe an apparent shift in angle based on the relativity of an object to its background of more distant objects.

paralax is used to measure distance. distance is determined my measuring a stars annual shift to paralax.

Front 4

What is a paralax angle?

Back 4

a paralax angle is the measurement of half a stars backand fourth shift over the course of a year. more distant objects have higher angles than closer objects. therefore stars with higher paralax angles are closer than stars with low paralax angles.

Front 5

What is a parasec?

Back 5

1 parasec equals an angle of 1 arcsecond. the abbreviation for which is pc. this changes as distance gets higher. when the distance

Front 6

how can we use parasecs to calculate luminosity?

Back 6

we must use the inverse square law for light.

Front 7

How do we state stellar luminosities?

Back 7

we state stellar luminosities in comparisson to our suns luminosity. this means that the luminosity will be multiplied by the luminosity of the sun.

the brighest stars are about a million times as luminous as the sun while he dimmest are about 1/10,000ths of the sun's luminosity. Our star is in the middle of this range but brighter than the majority of stars in our galaxy.

Front 8

Thermal radiation

Back 8

used to measure stellar temp.

hotter objects emit more light pua at all frequencies

hotter objects emit more photons with higher average energy

only surface tempeture can be directly measured.

Front 9

How do we determine surface tempetures?

Back 9

distance is not a factor

we determine this from the stars color or its spectrum the cooler the color the hotter the tempeture. blue-hot, red-cool

hottest stars are 50000k coolest 3000 k and our sun is 6000

Front 10

Why are spectral lines more accurate than spectral colors in determining tempetures?

Back 10

because colors can be affecte by interstellar dust. Lines of ionized elements must be fairly hot because it takes a high temp to ionize atoms (strangth...)

Spectral lines of molecules must be cool because there is not as much fusion and fusion takes high, high heat

Front 11

Spectral Type

Back 11

ranges from hottest to coolest tempetures of stars. Obafgkm

oh, be a find girl, kiss me. more lines in cooler styles.

Front 12

How do we measure stellar masses?

Back 12

we use newton's adjustment of keplers third law.

can only be applied when one object orbits the other.

must measure both orbit period and average orbital distance

Front 13

Bianary star systems

Back 13

half of all stars orbit a companion star of some kind and therefore members of bionary star systems.

Three classses

visual bianry-stars can see with a telescope.

spectral bianary-we can see doplar shifts in spectrums that determine the orbit.

Elipsing binary- we can measure periodic eclipses in our line of sight.

Front 14

When using the spectroscopic bianary what is the difference in results?

Back 14

the spectrocopic bianary will show two types of lines.

the double lined bionary shows a set spectrum from each star.

the single line bianary shows only one star because hte other is two dim but there are shifting lines in this bianary due to the second star.

Front 15

How do we measure mass using keplers third law?

Back 15

Keplers third law is period of time squared is equal to 4pi squared divided by gravity times the mass of planet one plus the mass of planet two the result of this is then multiplied by the average seperation (a) times itself three times. a3.

this can only be solved if the mass of both planets and p and a are known.

Front 16

What is the range of sizes of stars?

Back 16

100msun-~200msun

and the least massive are 0.08m sun.

Front 17

What is an H-R diagram?

Back 17

plots the lumiosity and tempeture of stars in a graph form. developed by hertzsprung russel.

it is based on the spectral sequence obafgkm.

tempetrue decresases from left to right on the verticle axis

the horizontal axis shows luminosity in units of the sun's luminosity.

because of this method, stars decrease rightward, or increase leftward.

Front 18

What is the main sequence of the HR diagram?

Back 18

it is the axis line that travelsin a straightish line at an angle from high to low in relation to low to high tempeture. High luminosity stars have low tempetures on the surace. stellar masses decrease downward along the main sequence.

Front 19

What doest it mean if a star has a lower tempeture and a higher luminosity of the main sequence? what does it mean if these factors are inversed?

Back 19

these stars must have a larger radii. these stars are called giants and supergiants.

the inverse of these relations are called qhite dwarfs

Front 20

what are main sequence stars in the process of doing?

Back 20

they are fusing hydrogen into helium in their cores. like our sun.

Front 21

How do hgier mass stars balance gravity?

Back 21

their core presssure and tempeture need to be larger.

Front 22

Review of stellar properties. What are the three stellar properties? what are their ranges?

Back 22

luminosity. ranges from approx 10-4LSun-106LSun

Temperature: color and spectral type ranges from approx 3000k-50000k.

Mass: determined form perid p and average seperation of bionary star orbit. ranges from 0.08msun to150msun.

Front 23

When will the sun run out of life? how are the lifespans of other suns determined mathematically?

Back 23

when the core hydrogen is used up so that there is less than 10% left.

if the star is ten times as large the star will use ten to the power of four times as fast

if it is 1/10th the size it will use fule 0.01 times as fast.

Front 24

How does the mass of a star determine its lifespan, luminosity, radius and color?

Back 24

high luminosity

short life

large radius

blue in color

low mass star is

low luminosity

long lived

small radius

red

Front 25

What are giants, supergiants and white dwarfs?

Back 25

They exist off the main sequence of the H-R diagram.

Giants and supergiants are stars nearing the end of their lives which have exhausted the supply of hydrogen fuel in tehir central cores and are facing an energy crisis trying to fend off the crush of gravity.

white dwarfs are the dead cores at the end of the fusion process. remaining embers. matter compressed to an extreamly high density.

Front 26

Variable stars are

Back 26

any star that varies significantly in brightness with time.

this happens sometimes when stars can't achieve proper balance between power wellign up from the cor and power radiated from the surface.

appearance of expanding and contracting that varies in brightness as it tries to find balance

Front 27

What is the Instability strip on the HR diagram?

Back 27

it is a strip that most pulsating variable stars inhabit.

Front 28

Cepheid variables are?

Back 28

the most luminus pulsing variable stars which lie in the upper portion of this strip. pulsing periods are closely realted to their luminosities. play an important role establishing distances to galaxies beyond milky way and revealing overall scale of the cosmos.