Ch.13
An arc minute is ______.
- 1/60 of a degree - a unit of angular size
Select all the stars that would have the same luminosity. (Use the Stefan-Boltzmann law.) Presented are the radii and temperatures of five stars compared to the Sun.
- 8 R☉, T☉ - 1/2 R☉, 4 T☉ - 2 R☉, 2 T☉
Select all the correct descriptions of binary stars.
- Binary stars are typically a few astronomical units apart. - Binary stars orbit each other around their common center of mass. - Astronomers use binary stars to calculate the masses of stars. - Hotter types of stars are most commonly in multiple
Which astronomers were instrumental in developing the type of plot of stars shown here?
- Henry Norris Russell - Ejnar Hertzsprung
Select the reasons why it is difficult to obtain direct images of stars (other than the Sun).
- Interferometry, which can resolve individual stars, is easier for larger and brighter stars. - The angular size of stars is smaller than the diffraction limit of even large single telescopes. - The atmosphere limits the capabilities of the largest telescopes, which are on Earth.
Select all that correctly describe the inverse-square law
- Light is less concentrated as it spreads out traveling away from its source. - It relates an object's luminosity to the square of its distance and its apparent brightness.
Select all the spectral properties that vary with temperature.
- The depth, or darkness, of spectral lines - Which lines are visible
Select the methods used to make direct measurements of the radii of stars.
- Using interferometry through simultaneous observations with two or more smaller telescopes - Observing with a space telescope above Earth's atmosphere - Using speckle interferometry with a high-speed camera
To use the method of standard candles, it is first necessary that astronomers ______.
- determine the actual luminosity of a single standard candle of the same type -independently determine the distance to a known standard candle of the same type - determine that the object is a standard candle and what kind, using spectroscopy or other means.
A spectrum of a glowing object such as a star ________.
- is a measurement of the amount of light, emitted as a function of wavelength - shows effects dependent on the surface temperature of the object - can be used to determine the elements present in the object
Spectroscopic binary
- light of two stars seen as single blob - detected by Doppler shift of emission/ absorption lines
From observations of a visual binary with a known distance, you obtain the semimajor axis, in AU, and the period, in years. If you plug those values into M = a3/P2, the mass you will find will be______.
- the sum of both stars' masses - in solar masses (M☉).
Visual binary
- two separate stars are seen - stars' orbits can be seen
red giants:
- very large - orange or red in color - relatively cool for stars
Possible masses of stars are given, in solar masses. Match these to indicate if the masses are typical, unexpected, or impossible.
0.01 : impossible. 100 : very uncommon. 2 : normal. 0.5 : normal and more common than the Sun. 25 : uncommon but normal.
Astrophysicists have determined that most stars form with masses between a lower limit of ______ M☉ to an upper limit of about ______ M☉.
0.1; 30
Rank the following stars by luminosity from the most luminous (top) to the least luminous (bottom).
1. Betelgeuse, a type M red giant 2. Sirius A, a type of A main-sequence star 3. the sun, a type of G main-sequence star 4. Procyon B, a white dwarf
Rank the following stars by radius from the largest (top) to the smallest (bottom).
1. Betelgeuse, a type M red giant 2. Sirius A, a type of A main-sequence star 3. the sun, a type of G main-sequence star 4. Procyon B, a white dwarf
Given their spectral classification, rank the following stars in order from hottest (top) to coolest (bottom).
1. Sirius, an A star 2. a G star 3. Aldebaran, a K star 4. Betelgeuse, an M star
Put the steps below in the correct order from beginning to end to describe how astronomers determine the chemical composition of stars.
1. Use a telescope to observe the spectrum of a star. 2. Measure the wavelengths of the absorption lines. 3. Compare observed absorption line wavelengths with know atomic spectra. 4. Determine composition by matches between observed absorption wavelengths and known wavelengths.
Absolute magnitudes of stars are defined as the apparent magnitude a star would have if you observed it from a distance of ______.
10 pc
A star with a parallax of 0.01 arc seconds would have a distance of ______. dpc=1/Parcsec.
100 parsecs (pc)
You observe a red star and measure its temperature to be 2900 K. Using Wien's law, find the wavelength of light at which it is the brightest.
1000 nm
Star A and B appear the same brightness. However, star B is about 100 times farther away than star A. This means that star B is also ____ times as luminous as star A.
100^2 = 10,000
The star Rigel has a luminosity of about 4 × 1031 watts. This is equivalent to how many solar luminosities?
10^5 Lo
The mass-luminosity relation predicts that a main-sequence star of 27 solar luminosities would have a mass of ______.
3
Two stars have the same luminosity. However, star A is about 9 times fainter than star B. This means that star A is______ than star B.
3 times farther away
There are _______ arc seconds in 1°.
3600
If a star is moving toward you at one one-hundredth the speed of light, by how many nanometers is a line at 500 nm shifted, and in what direction?
5 nm shorter (observed at 495 nm).
You observe two yellow G-type stars in a nearby star cluster at a known distance. One is 64 times brighter than the other. From this information, you can conclude that the brighter star has a radius ____ times larger than the dimmer one.
8
Using the mass-luminosity relation, we can predict that a star with a mass of 2 M☉ would have a luminosity of ______.
8 L
In a very old star cluster, one white dwarf is roughly three times hotter than a neighboring white dwarf. Since they are the same size, the hotter one emits _____ times more electromagnetic radiation than the cooler one.
81
The vast majority of the stars plotted on an H-R diagram, ______ % of them, create a line called the "main _______."
90; sequence
inverse-square law
A mathematical relationship in which a quantity varies in inverse proportion to the square of the distance from the source of the quantity.
space telescopes
Avoids blurring by the atmosphere
interferometry
Combines observations from multiple small telescopes
The very hottest stars
Extremely weak hydrogen lines
Which kind of binary system would be the fastest for making the measurements needed to use Kepler's third law to determine the mass of the stars?
Face-on visual binary with a short period
Astronomers Ejnar ___ and Henry Norris ___ independently developed the H-R diagram, a valuable tool for understanding stars.
Hertzsprung ; Russell.
describe the Hipparcos satellite:
It can measure distances to stars as far away as 250 parsecs. It measures parallaxes without the blurring effects of the atmosphere.
Two stars, Bobicus and Jakellax, appear close together in the sky. Jakellax exhibits a redshift in its spectrum, while Bobicus exhibits no Doppler shift at all. What can be said of their motion relative to the Sun?
Jakellax is moving away from the Sun, while Bobicus has no radial velocity.
Which astronomer discovered absorption lines in stellar spectra?
Joseph Fraunhofer
K and M stars
Molecular lines
The coolest stars
Molecular lines
Medium to low temperature stars
Multiple lines of metals such as calcium and iron
Which of the following statements about radial velocity is false?
Radial velocity occurs when an object moves in a circular orbit around the observer.
Select all that are axes in the H-R diagram.
Spectral type Luminosity Temperature
describe luminosity:
The Sun has a luminosity of about 4 × 1026 watts. Luminosity is measured in units of watts. A star's luminosity is one factor in how long it lives.
luminosity
The energy emitted per second as light, measured in watts
You observe two stars with the same temperature, but one of them has a higher luminosity than the other. How is this possible?
The more luminous star is larger. Both emit the same number of photons per area, but the larger star has a bigger surface area.
Use the Stefan-Boltzmann law to explain the dark spots seen on the Sun's surface (sunspots).
They are at a lower temperature than their surroundings and so emit less light and appear dark in contrast.
speckle interferometry
Uses a large telescope with a high-speed camera
Pretty hot stars
Very strong hydrogen lines
O star
Weak hydrogen lines and strong helium lines
Select the statements that are correct.
You can see stars with visual magnitudes from 0 to 6 in a dark sky, plus a few even brighter ones. The magnitude system was created by an ancient Greek astronomer to rank how stars appeared to the naked eye.
Paired stars in gravitational orbit around each other are called _____ stars.
binary
The ___ lines is the name for the set of hydrogen absorption lines that occur in the visible spectrum. These lines represent electron transitions from the n = 2 orbital.
blamer
The larger the value you measure for the parallax of a star, the _____ the star is.
closer
Triangulation as used in astronomy is a technique to measure:
distance
Astronomers measure the _______ shift of a star by recording its spectrum directly beside the spectrum of a standard, nonmoving source of light attached to the telescope.
doppler
The amount of ______ an object (such as a star) emits each second is called its ____ .
energy; luminosity
T/F: In the stellar luminosity classification system, the brightest supergiants are class Ib, and the majority of main-sequence stars are class IV.
false
T/F: Red giants are luminous because they are hot.
false
T/F: The absorption spectrum from a star will always show the spectral absorption lines of all the elements present in the surface layers.
false
T/F: The luminosity of a star changes depending on how far you are from it.
false
apparent brightness
how bright an object looks
Hydrogen makes up about 71% of the Sun, a G-type star, by mass. The fraction of hydrogen in other Sunlike stars ________.
is about the same
If you measured the parallax of a star from Mars instead of from Earth, you would expect the angle to be ______.
larger
Based on the relationship between radius and brightness, we know that if two stars have the same temperature but one is more luminous than the other, the more-luminous star must have a
larger radius than the dimmer star.
A bright star will have a ______ number as its absolute magnitude than a dimmer star.
lower
Astronomers try hard to find the distances to stars using methods such as parallax or the properties of variable stars because an independently determined distance and the easily measured brightness can be used to find the star's .
luminosity
Astronomers try hard to find the distances to stars using methods such as parallax or the properties of variable stars because an independently determined distance and the easily measured brightness can be used to find the star's _____.
luminosity
The inverse-square law relates an object's ________ to its and its ______ apparent brightness.
luminosity; distance
In the H-R diagram, the vertical axis is ______ and the horizontal axis is _____.
luminosity; surface temperature
The primary mission of the Hipparcos and Gaia satellites is to ______.
measure parallaxes of stars
F,G, and K stars
multiple lines of metals such as calcium and iron
Polaris and the star at the other end of the little Dipper, Kochab, are both apparent magnitude 2. In a photo of the night sky, they would appear similar to how they appear here in a planetarium simulation: larger than other stars. This is because ______. Multiple choice question.
of diffraction and resolution effects in the camera
A change in an object's apparent position caused by a change in the observer's position is known as ________.
parallax
Our brains estimate the distance to objects by using the method of ______. The baseline is the distance ______.
parallax; between our eyes
Stars moving across our line of sight show a steady, straight-line change in position over time. This is known as ________ motion.
proper
The ______ velocity is the source's speed along the line of sight of the observer.
radial
According to the Stefan-Boltzmann law, the green diagonal lines plotted on the H-R diagram show combinations of luminosity and temperature that result in stars that have the same ______.
radius
The Stefan-Boltzmann law describes how ______and ______ are related to luminosity.
radius ; temperature.
Stars located on a branch above and to the right of the Sun on the H-R diagram are large and cool. These are ______ giants.
red
Which types of binaries need to be seen edge-on, or at least somewhat tilted, for us to detect them as the type listed?
spectroscopic binaryeclipsing binary
A kind of star (or other celestial object) whose luminosity can be accurately predicted by studying its spectra or other properties is called a __________.
standard; candle.
If star A has a parallax twice as much as star B, you can conclude that ______.
star A is half as far as star B
You determine through spectroscopy that two stars are both a specific kind of standard candle. If the brightness of star Gamma is four times the brightness of star Delta, then Blank______.
star Gamma is half as far away
The variations in stellar spectra shown in this image are primarily a result of differences in the ___ of the star.
temperatures
The star Altair has a power output of about 4 × 1027 watts. This means that it produces as many joules of energy per second as _______ Suns and has a luminosity of _______ solar luminosities.
ten; ten
To determine the diameter of stars using the light curve of an eclipsing binary, astronomers measure ______.
the duration of the eclipse the Doppler shift of the stars how long it takes for the light to dim to full eclipse
Match the type of star to the luminosity classification. la : Ib: III: V:
the most luminous supergiants supergiants ordinary giants main sequence stars
Absorption lines in main-sequence stars (luminosity class V) are wider than the lines in supergiants (class I). Wider lines occur when the atoms producing them collide more frequently. The difference can be explained because ______.
the surfaces of main-sequence stars are denser
A spectrum shows the intensity of light as a function of wavelength. A light curve shows the intensity of light (at one or many wavelengths) as a function of ____.
time
The fundamental technique of _________ is a method that early astronomers used to find the distance to the Moon.
triangulation
T/F: If two stars have the same temperature but one is more luminous than the other, the more-luminous star must have a larger surface area, and therefore a larger radius than the dimmer star.
true
A star
very strong hydrogen lines
Stars located on a branch below and parallel to the main sequence on the H-R diagram are very hot, very small, and consequently somewhat dim. These are _____ dwarfs.
white
A binary star's orbital period is usually measured in units of
years
You observe the spectrum of a star in which a spectral line that is normally found at 434.1 nanometers is located at 433.9 nanometers instead. Calculate the star's radial velocity using the Doppler shift equation.
−0.2/434.1 × c = -138.1 kmsec
