Deck 10: Characterizing Stars

Question 1

Which property(ies)of a nearby star is/are determined by a measurement of stellar parallax?

A) spectral type and surface temperature
B) rotation period
C) apparent magnitude
D) distance from Earth

Answer 1

distance from Earth

Question 2

How far away is the nearest star beyond the Sun,in parsecs?

A) between 1 and 2 pc
B) about 12 pc
C) about 4 pc
D) between 1/2 and 1 pc

Answer 2

between 1 and 2 pc

Question 3

The first accurate measurement of stellar parallax was made in:

A) the fourth century b.c.e.
B) 1721.
C) 1838.
D) 1927.

Answer 3

1838.

Question 4

The MOST straightforward way to determine the distance to a nearby star involves the measurement of the:

A) star's spectrum.
B) ratio of the star's apparent and absolute magnitudes.
C) Zeeman effect of spectral lines in the star's spectrum.
D) star's parallax.

Question 5

Stellar parallax appears because:

A) Earth rotates about its own axis.
B) stars move in space.
C) stars have finite size (i.e., they are not really just points of light).
D) Earth moves in space.

Question 6

Parallax of a nearby star is used to estimate its:

A) surface temperature.
B) distance from Earth.
C) apparent magnitude.
D) physical size or diameter.

Question 7

How can we tell that some stars are relatively close to Earth in the sky?

A) The stars appear to move periodically back and forth against the background stars because of Earth's movement around the Sun.
B) The stars appear to be extremely bright and must therefore be very close to us.
C) The stars are occasionally occulted or eclipsed by the Moon; hence, they must be close.
D) The light from these stars shows only a very small redshift caused by the universal expansion of the universe, so they must be close.

Question 8

As you drive along a road,trees in the middle distance seem to shift in position relative to faraway hills.What name is given to this phenomenon?

A) parallax
B) perspective
C) Doppler effect
D) inverse-square law

Question 9

The motion that is used to change the position of the observer in the most common parallax measurements of distances to relatively nearby stars is the:

A) motion of the Sun around the galactic center.
B) change in latitude of the observation point on Earth.
C) motion of Earth in its orbit around the Sun.
D) rotation of Earth on its axis.

Question 10

Who was the first person to measure the parallax of a star successfully?

A) Sir George Airy in England
B) Henry Norris Russell in the United States
C) Tycho Brahe in Denmark
D) Friedrich Wilhelm Bessel in Germany

Question 11

In what fundamental way do we (and many other animals)utilize parallax for the measurement of distance?

A) Our eyes focus back and forth continuously, and the brain interprets the focusing in terms of distance to the object viewed.
B) The eye can measure the time taken for light to travel from an object, and the brain interprets this information in terms of distance to the object viewed.
C) We are always moving our heads slightly from side to side, and the brain compares look angles from each of these positions to obtain the distance to the object viewed.
D) Our eyes are mounted horizontally about 10 cm apart in our heads, and the brain interprets the relative look angles of these eyes in terms of distance to the object viewed.

Question 12

How many stars (other than the Sun)have an angle of parallax greater than 1 second of arc?

A) about a hundred
B) millions
C) none
D) only one

Question 13

What is parallax?

A) the distance to an object, measured in parsecs
B) the angle taken up by the size (e.g., diameter) of an object, as seen by an observer
C) the shift in angular position of an object as it moves in space
D) the apparent shift in position of an object as the observer moves

Question 14

How is stellar parallax defined?

A) Stellar parallax is the angle taken up by the diameter of a star as seen from Earth.
B) Stellar parallax is the angle subtended by the radius of Earth's orbit as seen from the star.
C) Stellar parallax is the angle subtended by the diameter of Earth's orbit as seen from the star.
D) Stellar parallax is the angle through which a star moves in our sky over the course of 1 year due to the motion of both the star and Earth.

Question 15

The MOST accurate stellar parallax measurements for distances to the majority of stars in our neighborhood of the universe have been made by:

A) the Hubble Space Telescope.
B) Friedrich Wilhelm Bessel, in 1838; no measurements since then have matched the precision of his measurements.
C) the Hipparcos satellite.
D) the Very Long Baseline Array of radio telescopes.

Question 16

We are about 8000 parsecs from the center of the Milky Way Galaxy,and the smallest parallax angle we can measure from orbiting observatories is about 0.001 arcseconds.How far toward the galactic center can we see with this technique (ignoring galactic dust and other obstacles)?

A) all the way to the center
B) about halfway to the center
C) about 1/8 of the way to the center
D) only 0.008 = 1/125 of the way to the center

Question 17

Stellar parallax is the:

A) inferred change in the distance to a star as its light is dimmed by passing through an interstellar cloud.
B) apparent shift seen in the position of a nearby star against more distant stars as Earth orbits the Sun.
C) difference between the apparent and absolute magnitudes of a star.
D) circular or elliptical motion of a star in a binary system as the two stars orbit each other.

Question 18

Which statement characterizes the human study of stellar evolution?

A) The changes in the observable cosmos over a human lifetime are profound.
B) A human lifetime is long enough to witness the evolution of a star through much of its evolutionary history.
C) We have never witnessed a significant change in any single star.
D) At any moment, we can see stars in every phase of evolution.

Question 19

How far away is the nearest star beyond the Sun?

A) about 1/4 ly away
B) about 1/10 ly away
C) about 4 ly away
D) between 1 and 2 ly away

Question 20

Aristotle (fourth century b.c.e.)rejected the idea that Earth moves because he knew stellar parallax motion would result,and he was unable to measure any.About how long after Aristotle was stellar parallax actually measured?

A) two centuries
B) 10 centuries
C) 22 centuries
D) 29 centuries

Question 21

The Hipparcos satellite was able to measure parallax for stars out to about 150 pc.This distance includes roughly 2.5 million stars.The new Gaia satellite should be able to measure the parallax of roughly a billion stars.Assuming the density of stars is approximately constant,what distance would this correspond to? (Hint: the volume of a sphere is proportional to the cube of the radius.)

A) 35 pc
B) 167 pc
C) 350 pc
D) 20 kpc

Question 22

A particular star is 20 pc away from Earth.What is the stellar parallax for this star?

A) 6 arcsec
B) 20 arcsec
C) 0.02 arcsec
D) 0.05 arcsec

Question 23

The triple-star system α Centauri has a parallax of 0.75 arcsec (the largest parallax known).How far is this star system from the Sun in light-years? (Careful with units!)

A) 4.35 ly
B) 0.41 ly
C) 1.33 ly
D) 0.75 ly

Question 24

Looking at the clock face on a distant steeple,the clock subtends an angle of 275 arcseconds.How far away is it?

A) 275 feet
B) 275 meters
C) 1/275 km
D) The distance cannot be computed from the given information.

Question 25

The Hipparcos satellite could measure stars up to approximately 150 pc away.What was the smallest parallax angle it could measure?

A) 150 arcsec
B) 1/150 arcsec
C) 1/150 degrees
D) 1/75 arcsec

Question 26

The Hipparcos satellite was able to measure parallax for stars out to about 150 pc.This distance includes roughly 2.5 million stars.What is the average number of stars in one cubic parsec?

A) 5.1 X 10-³
B) 0.18
C) 5.65
D) 8.84

Question 27

What is the relationship between stellar parallax (p)measured in seconds of arc and distance (d)measured in parsecs?

A) d = 1/p²
B) d = 1/p
C) d = p
D) d = p²

Question 28

A particular star has an angle of parallax of 0.2 arcsecond.What is the distance to this star?

A) 50 pc
B) 2 pc
C) 5 pc
D) 0.2 pc

Question 29

Sirius,in Canis Major (the large hunting dog of Orion),is the brightest star in the winter night sky.It has a parallax angle of 0.38 seconds of arc.The brightest star in Orion's other hunting dog,Canis Minor,is Procyon,with a parallax angle of 0.29 seconds of arc.Vega,in Lyra,the Lyre (Harp),is the brightest star in the summer night sky.It has a parallax angle of 0.13 seconds of arc.Which of these stars is farthest away?

A) Sirius
B) Procyon
C) Vega
D) The answer to the question cannot be determined from this information alone.

Question 30

If the Hipparcos satellite measures the parallax motion of a star against the background stars and concludes that the star has a parallax of 0.004 arcsec,how far is the star from Earth?

A) 25 pc, or 81.5 ly
B) 250 pc, or 815 ly
C) 400 pc, or 1300 ly
D) 0.004 pc, or 0.013 ly

Question 31

Stellar parallax as small as 0.01 arcsec can be measured using telescopes on Earth.To what distance does this measurement correspond in space?

A) 500 pc
B) 200 pc
C) 0.01 pc
D) 100 pc

Question 32

In 2013,the European Space Agency launched the Gaia mission,which will measure parallax angles down to 10-⁵ arcseconds.What distance does this correspond to?

A) 10-⁵ pc
B) 10⁵ light-years
C) 100 kpc
D) 200 kpc

Question 33

How far out into space can distances be determined using telescopes on Earth if stellar parallax values no smaller than 0.01 arcsec can be measured?

A) 10 pc
B) 100 pc
C) 500 pc
D) 2000 pc

Question 34

How much can we learn about a star from a measurement of its apparent magnitude?

A) its intrinsic brightness (the total light actually emitted by the star)
B) the brightness the star would appear to have if it were exactly 10 pc from Earth
C) the brightness of the star as it appears in Earth's sky
D) the total output of electromagnetic energy emitted at all wavelengths from the star

Question 35

A star is 80 pc from the Sun.Its apparent motion against the background sky as a result of Earth's motion through 1 AU; that is,its stellar parallax,is:

A) 0.0125 arcsecond.
B) 0.0125 arcminute.
C) 0.0125 radian, or 0.72°.
D) 80 arcseconds.

Question 36

Apparent magnitude is a measure of a star's:

A) intrinsic brightness (actual light output).
B) size (diameter).
C) temperature.
D) brightness, as seen from Earth.

Question 37

The semimajor axis of Pluto's orbit is almost 40 AU.The smallest parallax angle we can measure from orbiting observatories is about 0.001 arcsec.Suppose we use this technique to measure parallax from Pluto's orbit (over the course of half a Pluto "year").What is the maximum distance we could measure?

A) 40 pc
B) 1000 pc
C) 40,000 pc
D) 80,000 pc

Question 38

If a nearby star shows a parallax of 0.5 arcsec (when Earth moves through 1 AU,by definition),what is its distance from Earth,in light-years?

A) 2 ly
B) 1.83 ly
C) 6.52 ly
D) 3.26 ly

Question 39

A particular star has an angle of parallax of 0.1 arcsec.What is the distance to this star?

A) about 10 ly
B) about 33 ly
C) about 0.1 ly
D) about 3.3 ly

Question 40

Two of the brightest stars in Orion are Betelgeuse (apparent magnitude = 0.45)and Rigel (apparent magnitude = 0.15).From this information,you can determine that Betelgeuse is:

A) brighter than Rigel.
B) bigger than Rigel.
C) farther away than Rigel.
D) None of the answers is correct..

Question 41

The star Alphard has an apparent magnitude of 2.0,and the star Megrez has an apparent magnitude of 3.3.The only thing that can be said with certainty about Alphard is that it is _____ than Megrez.

A) brighter, as seen in Earth's sky,
B) more luminous
C) fainter, as seen in Earth's sky,
D) closer to Earth

Question 42

A star of apparent magnitude +3.5 appears _____ than a star of apparent magnitude +3.3.

A) farther away
B) fainter
C) either brighter or fainter, depending on the distance to the stars,
D) brighter

Question 43

The modern system of apparent magnitudes uses the star Vega as its basis.In this scheme,Vega is defined to have an apparent magnitude of:

A) 10.
B) 1.0.
C) 0.0.
D) -1.0.

Question 44

A star of apparent magnitude +5 appears _____ than a star of apparent magnitude +3.

A) fainter
B) farther away
C) brighter
D) either brighter or fainter, depending on the distance to the stars,

Question 45

A list of four stars and their apparent magnitudes is given.Which star looks brightest when viewed from Earth?

A) Tau Ceti m = +3.49
B) Alpha Centauri B m = 1.34
C) Barnard's star m = +9.53
D) 61 Cygni A m = +5.21

Question 46

Which star,according to its apparent magnitude,would NOT be visible to the unaided eye on a clear night?

A) Tau Ceti m = +3.49
B) Alpha Centauri B m = 1.34
C) Barnard's star m = +9.53
D) 61 Cygni A m = +5.21

Question 47

The statement that the apparent magnitude of a variable star has increased indicates that its:

A) brightness has increased.
B) surface temperature has decreased.
C) brightness has decreased.
D) surface temperature has increased.

Question 48

A star of apparent magnitude -2 appears _____ than a star of apparent magnitude -3.

A) fainter
B) brighter
C) farther away
D) either brighter or fainter, depending on the distance to the stars,

Question 49

A star that has an apparent magnitude of 0 (see Figure 10-2,Comins,Discovering the Essential Universe,6th ed.)would:

A) be fainter than Spica (α Virginis), which has an apparent magnitude of +1.0.
B) be brighter than Deneb (α Cygni), which has an apparent magnitude of +1.2.
C) have infinite brightness since 1/0 = infinity.
D) not be emitting any light and therefore could not be seen from Earth.

Question 50

As you move closer to a star,which two of its properties change?

A) luminosity and absolute magnitude
B) Luminosity and absolute magnitude
C) absolute magnitude and brightness
D) apparent magnitude and brightness

Question 51

A star's absolute magnitude and its apparent magnitude have the same numerical value.How far is this star from Earth?

A) It is not possible for a star to have the same absolute and apparent magnitudes.
B) The star would have to be an infinite distance away.
C) 10 ly
D) 10 pc

Question 52

The ancient Greek astronomer Hipparchus introduced the magnitude scale on which he called the brightest stars first magnitude.Today,the brightest star in the night sky is Sirius,with a magnitude of -1.4,considerably brighter than first magnitude.Why the discrepancy?

A) Sirius was formed since the era in which Hipparchus lived.
B) Sirius existed during Hipparchus's lifetime, but it has obviously brightened considerably since then.
C) Hipparchus had poor eyesight and made many classification errors.
D) After using modern scientific instruments to measure the actual energy output of stars, astronomers modified the magnitude scale of Hipparchus.

Question 53

A star of apparent magnitude +4.7 appears _____ than a star of apparent magnitude +4.8.

A) brighter
B) either brighter or fainter, depending on the distance to the stars,
C) farther away
D) fainter

Question 54

If you look out at the night sky,the number of stars with:

A) each magnitude (first, second, etc.) is about the same.
B) smaller magnitude numbers is much larger than the number of stars with larger magnitude numbers.
C) larger magnitude numbers is much larger than the number of stars with smaller magnitude numbers.
D) magnitudes around 3 is larger than either the number with magnitudes around 2 or the number with magnitudes around 4.

Question 55

The relative brightness of a star as we see it in Earth's sky is called:

A) absolute magnitude.
B) apparent magnitude.
C) surface temperature.
D) luminosity.

Question 56

A star of apparent magnitude -1.5 appears _____ than a star of apparent magnitude +2.0.

A) farther away
B) fainter
C) brighter
D) either brighter or fainter, depending on the distance to the stars,

Question 57

A star of apparent magnitude +1 appears _____ than a star of apparent magnitude +2.

A) either brighter or fainter, depending on the distance to the stars,
B) farther away
C) brighter
D) fainter

Question 58

If you look out at a clear night sky with the unaided eye,the faintest stars you can see have magnitudes around:

A) -6.
B) 0.
C) +6.
D) +12.

Question 59

By approximately how many magnitudes is the star Sirius fainter than the full Moon in our sky? (See Figure 10-2,Comins,Discovering the Essential Universe,6th ed.)

A) 15
B) 2
C) 11
D) 5

Question 60

A star of apparent magnitude +2.1 appears _____ than a star of apparent magnitude -1.2.

A) farther away
B) fainter
C) brighter
D) either brighter or fainter, depending on the distance to the stars,

Question 61

Light leaving a point source spreads out so that the apparent brightness I of light per unit area varies with distance d according to which law ( means "proportional to")?

A) I = constant
B) I 1/d²
C) I d²
D) I 1/d

Question 62

The absolute magnitude of a star is the brightness the star would appear to have if it were placed at what distance from Earth?

A) 32.6 ly
B) distance to the galactic center
C) 10 ly
D) 1 AU

Question 63

If we restrict our measurements to a specific band of color or wavelength using an optical filter,what observations of a star are necessary to determine the absolute magnitude of the star at this color?

A) distance and temperature
B) apparent magnitude and temperature
C) just apparent magnitude since absolute magnitude is simply apparent magnitude +5
D) apparent magnitude and distance

Question 64

What is the ratio of the light energy that falls on a unit area of Mercury's surface compared to that falling on a unit area of Earth's Moon if Mercury is at 0.4 AU and the Moon is at 1.0 AU from the Sun?

A) 1
B) 6.25
C) 2.5
D) 16

Question 65

The Sun's luminosity is 3.83 × 10²⁶ watts.By the time this energy reaches Earth,it has spread out so that it provides only 1370 watts to each square meter.The orbit of Mars has a mean radius of 1.53 AU.How many watts of the Sun's luminosity are provided to each square meter of the surface of Mars?

A) 34
B) 153
C) 585
D) 1578

Question 66

What is the fundamental difference between absolute and apparent magnitude of a star?

A) The difference is +5 since absolute and apparent magnitude differ by this value by definition.
B) Apparent magnitude depends on the star's temperature, whereas absolute magnitude is independent of temperature.
C) Apparent magnitude depends on the size of the star, whereas absolute magnitude is independent of this parameter.
D) Absolute magnitude is an intrinsic property of the star, whereas apparent magnitude depends on its distance from Earth.

Question 67

What is the intensity of sunlight per square meter reaching Venus compared with this intensity at Earth's orbital distance? (For orbital radii,see Appendix,Table C-1,Comins,Discovering the Essential Universe,6th ed.)

A) about the same, since this intensity remains constant, following a law of nature
B) about 1.4
C) about 1.9
D) about 0.5

Question 68

The intensity of sunlight per square meter reaching Jupiter is approximately what fraction of that at Earth's orbital distance? (For orbital radii,see Appendix,Table C-1,Comins,Discovering the Essential Universe,6th ed.)

A) 25 times
B) about the same
C) 1/5
D) 1/25

Question 69

Viewed from Earth,the Sun's absolute magnitude is M = 4.8 and its apparent magnitude is m = -26.7.Viewed from Neptune,30 AU from the Sun,the Sun's apparent magnitude is:

A) 4.8.
B) 12.8.
C) -19.3.
D) -26.7.

Question 70

Two stars,P and Q,can be seen in the same region of Earth's sky with the same apparent magnitude,but star Q is twice as far away as star P.What is the ratio of the luminosities of these stars (star P/star Q)?

A) 4
B) 2
C) 1/4
D) 1/2

Question 71

Star A has luminosity LA = 100 L⊙ and it is 1000 pc away.Star B has the same luminosity as the Sun,L⊙,and it is 100 pc away.What can you say about the brightnesses of these two stars?

A) Star A is brighter than star B.
B) Star B is brighter than star A.
C) Star A and star B have the same brightness.
D) It is not possible to answer the question without knowing L⊙, the luminosity of the Sun.

Question 72

The star α Centauri C and the star Groombridge 34 B have the same apparent magnitude,but α Centauri C is 1.3 pc away from Earth and Groombridge 34 B is 3.5 pc away.What is the luminosity of Groombridge 34 B compared with α Centauri C? (See Figure 10-3,Comins,Discovering the Essential Universe,6th ed.)

A) 2.7 times brighter
B) 7.2 times fainter
C) 2.7 times fainter
D) 7.2 times brighter

Question 73

Suppose the distance between an observer and a lightbulb is doubled.How does its final brightness compare with its initial brightness?

A) The lightbulb appears 1/16 as bright.
B) The lightbulb appears 4 times brighter.
C) The lightbulb appears 1/2 as bright.
D) The lightbulb appears 1/4 as bright.

Question 74

Absolute magnitude is defined as the apparent magnitude that a star would have if:

A) all the energy from the star were concentrated in the visual region.
B) it were located at exactly 10 ly from Earth.
C) it were located at exactly 10 pc from Earth.
D) it were located at exactly 10 AU from Earth.

Question 75

The Sun has an absolute magnitude of +4.8.How far away would we have to be for the Sun to be just barely visible to the unaided eye (sixth magnitude)?

A) 1.2 pc
B) 6 pc
C) 17.4 pc
D) 22.4 pc

Question 76

A star has an absolute magnitude M = 1.69 and an apparent magnitude m = 1.04.How far away is this star? (Hint: this question does not require a detailed calculation.)

A) 24.2 ly
B) 43.2 ly
C) 59.7 ly
D) 160.2 ly

Question 77

Suppose that two identical stars (they have the same total light output)are located so that star A is at a distance of 5 pc and star B is at a distance of 25 pc from Earth.How will star B appear,compared with star A?

A) Star B will be 1/5 as bright as star A.
B) Star B will be 1/25 as bright as star A.
C) Star B will be 1/2.2 as bright as star A.
D) Star B will be 1/20 as bright as star A.

Question 78

For most stars,the:

A) absolute magnitude is a larger number than the apparent magnitude.
B) apparent magnitude is a larger number than the absolute magnitude.
C) absolute magnitude and the apparent magnitude are numerically equal.
D) chances are about even of the apparent magnitude being larger or the absolute magnitude being larger.

Question 79

Viewed from Earth,the Sun's absolute magnitude is M = 4.8 and its apparent magnitude is m = -26.7.Viewed from Neptune,30 AU from the Sun,the Sun's absolute magnitude is:

A) 4.8.
B) 12.8.
C) -19.3.
D) -26.7.

Question 80

Luminosity is measured in:

A) watts.
B) watts per second.
C) watts per square meter.
D) parsecs.