Ast 2002 Exam 3 (Ch11-13)

Front 1

Before we can use parallax to measure the distance to a nearby star, we first need to know __________.

Back 1

the Earth-Sun distance

Front 2

Which of the following is a valid way of demonstrating parallax for yourself?

Back 2

Hold up your hand in front of your face, and alternately close your left and right eyes.

Front 3

What is the cause of stellar parallax?

Back 3

Earth's orbit around the Sun.

Front 4

The more distant a star, the __________.

Back 4

smaller its parallax angle

Front 5

Approximately what is the parallax angle of a star that is 20 light-years away?

Back 5

0.16 arcsecond

d(in light years)=3.26 X 1/p(in arcseconds)

Front 6

Suppose that a star had a parallax angle of exactly 1 arcsecond. Approximately how far away would it be, in light-years?

Back 6

3.3 light-years

Front 7

The total amount of power (in watts, for example) that a star radiates into space is called its _________.

Back 7

luminosity

Front 8

According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples?

Back 8

Its apparent brightness will decrease by a factor of 9.

Front 9

Assuming that we can measure the apparent brightness of a star, what does the inverse square law for light allow us to do?

Back 9

Calculate the star's luminosity if we know its distance, or calculate its distance if we know its luminosity.

Front 10

If star A is closer to us than star B, then Star A's parallax angle is _________.

Back 10

larger than that of Star B

Front 11

What do we need to measure in order to determine a star's luminosity?

Back 11

apparent brightness and distance

Front 12

If the star Alpha Centauri were moved to a distance 10 times farther than it is now, its parallax angle would

Back 12

get smaller.

Front 13

We divide the electromagnetic spectrum into six major categories of light, listed below. Rank these forms of light from left to right in order of increasing wavelength. To rank items as equivalent, overlap them.

Back 13

Far left: gamma rays, x rays, ultraviolet, visible light, infrared, radio waves :Far Right

Visible light spans only a very narrow range of wavelengths, from about400 nanometers at the blue (violet) end to about 700 nanometers at the red end.

Front 14

Rank the forms of light from left to right in order of increasing frequency. To rank items as equivalent, overlap them.

Back 14

Far Left: Radio Waves, infrared, visible light, ultraviolet, x rays, gamma rays :Far Right

Because the speed of light is a constant, longer wavelengths must mean lower frequencies, and vice versa

Front 15

Rank the forms of light from left to right in order of increasing energy. To rank items as equivalent, overlap them.

Back 15

Far Left: radio waves, infrared, visible light, ultraviolet, x rays, gamma rays :Far Right

the energy of a photon of light is proportional to its frequency

Front 16

Rank the forms of light from left to right in order of increasing speed. To rank items as equivalent, overlap them.

Back 16

all forms of light travel at the same speed, regardless of wavelength, frequency, or energy.

Front 17

A spectral line that appears at a wavelength of 321 nm in the laboratory appears at a wavelength of 328 nm in the spectrum of a distant object. We say that the object's spectrum is:

Back 17

redshifted.

Front 18

The diagrams below each show the motion of a distant star relative to Earth (not to scale). The red arrows indicate the speed and direction of the star’s motion: Longer arrows mean faster speed. Rank the stars based on the Doppler shift that we would detect on Earth, from largest blueshift, through no shift, to largest redshift.

Back 18

blueshift: longest arrow pointing towards Earth, shorter arrow pointing towards Earth, arrow pointing down and away from Earth, shorter arrow pointing up and away from Earth, longer arrow pointing up and away from Earth :redshift

the star moving fastest toward Earth will have the greatest blueshift, the star moving across our line of sight will have no shift at all, and the star moving fastest away from us will have the greatest redshift.

Front 19

Each diagram below shows a pair of spectra with a set of spectral lines. The top spectrum always shows the lines as they appear in a spectrum created in a laboratory on Earth (“Lab”) and the bottom spectrum shows the same set of lines from a distant star. The left (blue/violet) end of each spectrum corresponds to shorter wavelengths and the right (red) end to longer wavelengths. Rank the five stars based on the Doppler shifts of their spectra, from largest blueshift, through no shift, to largest redshift.

Back 19

lines that are shifted to the left (toward the blue/violet) compared to the laboratory spectrum represent blue shifts, and lines shifted to the right (toward the red) represent redshifts.

Front 20

An important line of hydrogen occurs at a rest wavelength (as measured in a laboratory) of 656 nm (a nanometer (nm) is a billionth of a meter). Each diagram below has this line labeled with its wavelength in the spectrum of a distant star. Rank the motion of the stars along our line of sight (radial motion) based on their speed and direction, from moving fastest toward Earth, through zero (not moving toward or away from Earth), to moving fastest away from Earth.

Back 20

toward Earth: 646 nm, 650 nm, 656 nm, 657 nm, 663 nm :Away from Earth

This ranks the stars in wavelength order. The first two stars are moving toward us, because their lines have wavelength shorter than the rest wavelength of 656 nm. The last two stars are moving away from us, because their lines have wavelength longer than the rest wavelength of 656 nm.

Front 21

All stars spend approximately the same amount of time on the main sequence.

Back 21

false

Front 22

Most stars on the main sequence fuse hydrogen into helium in their cores, but some do not.

Back 22

false

Front 23

Blue stars are always more luminous than red stars

Back 23

false

Front 24

Two stars both lie on the main sequence. Star X is spectral type A, while Star Y is spectral type G. Star X must be more massive than Star Y.

Back 24

true

Front 25

Two stars have the same spectral type. Star X is in luminosity class III, while Star Y is in luminosity class V. Star X must be larger in radius than Star Y.

Back 25

true

Front 26

The approximate main-sequence lifetime of a star of spectral type O is ________.

Back 26

3 million years

Front 27

The figure shows a standard Hertzsprung-Russell (H-R) diagram. Label the horizontal and vertical axes using the two blanks nearest the center of each axis, and label the extremes on the two axes using the blanks on the ends of the axes.

Back 27

top to bottom: brighter, luminosity, fainter

left to right: hotter, surface temperature, colder

Front 28

Use the labels to identify what kinds of stars inhabit each region of the the H-R diagram.

Back 28

top to bottom: supergiants, main sequence, red giants, main sequence, white dwarfs

Front 29

The diagonal lines on the H-R diagram represent lines along which all stars would have the same radius. Label the three white lines with the correct values for the radii of stars that fall on them.

Back 29

top to bottom: 1000 solar radii, 1 solar radius, 1 Earth radius

Stellar radii increase diagonally on the H-R diagram from the lower left to the upper right.

Front 30

The position of a star along the main sequence tells you both its mass and its hydrogen-burning lifetime. Label the indicated blanks on the main sequence with the approximate lifetimes of stars at those positions.

Back 30

top to bottom: 10 million year lifetime, 10 billion year lifetime, 100 billion year lifetime

Stars spend most of their lives on the main sequence, where they generate energy by fusing hydrogen into helium in their cores. High-luminosity stars have much shorter main-sequence lifetimes than lower luminosity stars, because they burn through their supply of hydrogen at a much faster rate

Front 31

Listed following are several fictitious stars with their luminosities given in terms of the Sun’s luminosity (LSun) and their distances from Earth given in light-years (ly). Rank the stars based on how bright each would appear in the sky as seen from Earth, from brightest to dimmest. If two (or more) stars have the same brightness in the sky, show this equality by dragging one star on top of the other(s).

Back 31

Brightest: Nismo, Shelby and Ferdinand overlap, Enzo, Lotus :Dimmest

Front 32

Listed following is the same set of fictitious stars given in Part A. Rank the stars based on how bright each would appear in the sky as seen from Jupiter, from brightest to dimmest.

Back 32

Brightest: Nismo, Shelby and Ferdinand overlap, Enzo, Lotus :Dimmest

Stars are so far away that any difference in distance to the stars from Earth and Jupiter is negligible. As a result, the answer to this part is the same as the answer to Part A.

Front 33

The following figure shows how four identical stars appear in the night sky seen from Earth. The shading is used to indicate how bright (white) or dim (dark gray) the star would appear in the sky from Earth. Rank the stars based on their distance from Earth, from farthest to closest.

Back 33

left to right: The darkest to the left and brightest to the right

apparent brightness decreases with distance

Front 34

Compared to a main-sequence star with a short lifetime, a main-sequence star with a long lifetime is __________.

Back 34

less luminous, cooler, smaller, and less massive

Front 35

Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________.

Back 35

cooler and larger in radius

Front 36

Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________.

Back 36

hotter and smaller in radius

Front 37

Listed following is a set of statements describing individual stars or characteristics of stars. Match these to the appropriate object category.

Back 37

red giant or supergiant: very cool but very luminous, found in the upper right of the H-R diagram

Main sequence: the sun for example, the majority of stars in our galaxy, the hottest and most luminous

white dwarfs: not much larger in radius than earth, very hot but very dim

Front 38

Binary Stars

Back 38

consists of 2 stars orbiting their common center mass

Front 39

Majority of Stars in our Galaxy are...

Back 39

Binary Stars

Big Dipper (Mizar)

Front 40

Hipparcos Telescope

Back 40

precise distant measurement by parallax

could map the height of astronaut on moon

Front 41

Kepler Telescope

Back 41

small slice of Milky way

variations in light of nearby stars

looking for exoplanets

designed to notice light curves in stars

Front 42

Gaia Telescope

Back 42

devoted to angular position

Similar to Hipparcos

Map width of a button of man on moon

Front 43

ASTRO

Back 43

devoted to star angular position measurements

Front 44

The Kepler Spacecraft searched for exoplanets in this way?

Back 44

Finding dips in parent star's light curve

Front 45

The Kepler team found that multiple exoplanet systems are?

Back 45

Relatively common, hundreds found

Front 46

Gaia can get a measurement of a star's true angular position by?

Back 46

Getting a new position measurement every year

Front 47

How many parsecs is the distance to 61 Cygni?

Back 47

3.18 parsecs

D=1/0.314=3.18pc

Front 48

61 Cygni is 3.18 pc away from Earth. How many LY is that?

Back 48

10.4 LY

3.14 x 3.26=10.4

Front 49

If a stars apparent magnitude m is less than its absolute magnitude M then?

Back 49

the star is closer than 10pc

Front 50

Low magnitude

Back 50

Brighter

Front 51

Higher magnitude

Back 51

Dimmer

Front 52

This star is brighter than the others if viewed from Earth?

Back 52

Vega

Front 53

This star is intrinsically brighter than the others?

Back 53

Antares

Front 54

Spectral Type order

Back 54

OBAFGKM

Front 55

What is it's surface Temperature if max=834nm.

maxT=0.0028977mK

Back 55

T=3474

Front 56

Betelguese

Back 56

cooler the sun

red supergiant

mass= 7.7

Front 57

Color reveals

Back 57

surface temperature

Front 58

Luminosity reveals

Back 58

total energy output

Front 59

Every sq meter of red star surface has the same luminosity owing to the Stefan-Boltzman law

Back 59

joules/sec

__________

m^2=6T^4

Front 60

You have one sq meter of the surface of a red M-class star and a sq meter of the surface of a blue O-type star. Which sq meter produces more energy per sec?

Back 60

O-class

Front 61

Why does it's sq meter produce more joules of energy per second?

Back 61

temperature

Front 62

How do you interpret a star in the upper right of the H-R diagram: red, spectral type M, very luminous

Back 62

Its diameter is larger than the main seq M-type stars

Bigger=Brighter

Front 63

UBV band

Back 63

Star brighter in B band than V band

U=384nm

B=442nm

V=540nm