Chapter 13 Measuring a stars distance
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
Rank the stars according to their size (radius) with the largest at the top.
1. A star found in the upper right of the HR diagram 2. A blue main-sequence star 3. The sun 4. A sar in the lower right of the HR diagram. 5. A white dwarf with a surface temperature of 20,000 K
Rank these nearby stars in order of increasing luminosity (top to bottom). Absolute magnitudes are given by M and apparent magnitudes by m.
1. Barnards star 2. Procyon 3. A centauri 4. sun 5. Sirius
Put the steps below in the correct order from beginning to end to describe how astronomers determine the chemical composition of stars.
1. Use the telescope to observe the spectrum of a star. 2. Measure the wavelengths of the absorption lines. 3. Compare observed absorption line wavelength with know atomic spectra. 4. Determine composition by matches between observed absorption wavelengths and known wavelengths
Arrange the steps to explain how an astronomer could determine the luminosity of a star.
1. take one image and measure the brightness of the star 2. Using a second image, measure the change in position of the star over half a year 3. Determine the distance to the star form parallax 4. Use the inverse-squarelaw
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.
1/2 R☉, 4 T☉ 2 R☉, 2 T☉ 8 R☉, T☉
Absolute magnitudes of stars are defined as the apparent magnitude a star would have if you observed it from a distance of ____.
10 pc
Two stars, a red giant and a blue supergiant, are the same size. If the temperature of the blue supergiant is 10 times the temperature of the red giant, how many times more luminous is the blue star?
10,000
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?
105 L☉
Rigel has a temperature roughly twice that of the Sun, and a radius about 80 times larger. Accordingly, we expect Rigel's luminosity to be about ____ solar luminosities. (You can look Rigel up on an H-R diagram and check your result.)
10^5
Through various measurements, you find that the semimajor axis in a binary consisting of a red giant and a yellow G-type star is 4 AU. The period is determined to be 2 years. Therefore, the combined mass of the system is ____M☉.
16
You observe a blue star and measure its temperature to be 10,000 K. At what wavelength of light is it the brightest?
290 nanometers
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
Astrophysicists have determined that most stars form with masses between a lower limit of ____ M☉ to an upper limit of about ____ M☉. (Select two answers.)
30 0.1
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)
Match the elements found in stars to what percentage of the star they comprise (percentages are given by mass).
71%- Hydrogen 27%- Helium 2%- Oxygen, carbon, and other elements
Which spectrum represents an object emitting the highest number of red photons?
A
You observe a planet orbiting around a star. At which of the labeled positions do you see a radial velocity?
A C
Three observers at different positions (A, B, C) observe a star moving in the direction of the arrow. Match their positions with the color of Doppler shift they will observe.
A- redshift b-no shift c- blue shift
Select all that correctly describe the spectrum in the picture.
Absorption lines allow astronomers to tell the composition of a star. Stellar absorption lines are created when light passes through the upper layers of a star. Each type of atom produces a unique set of absorption lines.
Which astronomer discovered that stellar spectra made more sense if arranged in order of their blackbody color temperature?
Annie Jump Cannon
Match the astronomer or scientist to his or her contribution to stellar spectroscopy.
Annie Jump Cannon- Revised the calssification system to be based on temp Henry Draper- Classified stella spectra with a letter system Joseph Fraunhofer- Discovered absorption lines in the Sun's spectrum Cecilia Payne-Gaposchkin- Recognized that the strength of lines strongly depends on temperature M. Saha- Discovered how to calculate the most likely energy level for electrons in an atom.
Match the terms to their definitions.
Apparent double star- two stars that appear close together from Earth but are not actually orbiiting each other binary star- two stars orbiting eachother Eclipsing binary- Binary system seen edgeon from earth spectroscopic binary- binary in which the stars cannot be seen separately but spectral measurements show two Doppler shifts visual binary- binary system in which the star are seen
Select all that are correct about visual and spectroscopic binaries.
Astronomers can determine the orbit speed for both types. Astronomers can determine the orbit size for both types.
Based on the location of the peak of the emission, the spectral type for a star with the spectrum shown in the image is most likely ____.
B
The hydrogen lines in the visible spectrum are known as ____ lines, after the scientist who discovered their pattern of wavelengths.
Balmer
cSelect all the correct descriptions of binary stars.
Binary stars orbit each other around their common center of mass. Astronomers use binary stars to calculate the masses of stars. Binary stars are typically a few astronomical units apart. Hotter types of stars are most commonly in multiple-star systems.
There are____arc seconds in 1°. (Please enter a whole number instead of words.)
Blank 1: 3,600 or 3600
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.
Blank 1: 81, eighty-one, eightyone, or eighty one
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.
Blank 1: Balmer
Astronomers Ejnar_____ and Henry Norris____ independently developed the H-R diagram, a valuable tool for understanding stars.
Blank 1: Hertzsprung Blank 2: Russell
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
Blank 1: eight or 8
The amount of____an object (such as a star) emits each second is called its_______
Blank 1: energy or light Blank 2: 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_________
Blank 1: luminosity
The inverse-square law relates an object's____to its____and its apparent brightness.
Blank 1: luminosity Blank 2: distance
The figure demonstrates the concept behind the measurement of distance using the method of
Blank 1: parallax
The figure demonstrates the concept behind the measurement of distance using the method of____
Blank 1: parallax
Stars moving across our line of sight show a steady, straight-line change in position over time. This is known as
Blank 1: proper
A kind of star (or other celestial object) whose luminosity can be accurately predicted by studying its spectra or other properties is called a__________ ____________
Blank 1: standard Blank 2: candle
Rigel has a temperature roughly twice that of the Sun, and a radius about 80 times larger. Accordingly, we expect Rigel's luminosity to be about ____ solar luminosities. (You can look Rigel up on an H-R diagram and check your result.)
Blank 1: temperature Blank 2: radius, size, or area
The variations in stellar spectra shown in this image are primarily a result of differences in the______ of the star
Blank 1: 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.
Blank 1: ten or 10 Blank 2: ten or 10
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 ________.
Blank 1: time
A binary star's orbital period is usually measured in units of
Blank 1: years
Which of these spectra is from the object that would look the reddest?
C
Which of these stars appears the brightest from Earth?
Canopus, magnitude -0.74
Which astronomer explained why the temperature of a star affected the depth of the absorption lines in the spectrum?
Cecilia Payne-Gaposchkin
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
True or false: The absorption spectrum from a star will always show the spectral absorption lines of all the elements present in the surface layers.
False
True or false: The luminosity of a star changes depending on how far you are from it.
False
Select all that correctly describe the Hipparcos satellite.
It measures parallaxes without the blurring effects of the atmosphere. It can measure distances to stars as far away as 250 parsecs.
Select all that correctly describe the inverse-square law.
It relates an object's luminosity to the square of its distance and its apparent brightness. Light is less concentrated as it spreads out traveling away from its source.
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
Rank the following stars from hottest (top) to coolest (bottom).
Lota Orionis SPica Mizar caph arcturus betelgeuse
Match the terms to their descriptions.
Luminosity- The energy emotted per second as light, measured in watts Apparent brightness- How bright an object looks Inverse-square law- A mathematical relationship between how bright an object looks, how much energy it emits, and its distance squared
Based on the location of the peak of the emission, the spectral type for a star with the spectrum shown in the image is most likely ____.
M
Match the spectral features to the correct spectral types.
O star- Weak hydrogen lines and strong helium lines A star- very strong hydrogen lines K and M stars-Molecular lines F, G and K 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.
Given their spectral classification, rank the following stars in order from hottest (top) to coolest (bottom).
Siruis, a g star aldebaran betelgeuse
Select all that correctly 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.
Select the reasons why it is difficult to obtain direct images of stars (other than the Sun).
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. Interferometry, which can resolve individual stars, is easier for larger and brighter stars.
Select the statements that are correct.
The magnitude system was created by an ancient Greek astronomer to rank how stars appeared to the naked eye. You can see stars with visual magnitudes from 0 to 6 in a dark sky, plus a few even brighter ones.
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.
Match the spectral features to the correct temperature ranges.
The very hottest stars- extremely weak hydrogen lines Pretty hot stars- Very strong hydrogen lines The coolest stars- molecular lines Medium to low temperature stars- Multiple lines of metal such as calcium and iron
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.
Select the methods used to make direct measurements of the radii of stars.
Using speckle interferometry with a high-speed camera Observing with a space telescope above Earth's atmosphere Using interferometry through simultaneous observations with two or more smaller telescopes
Match the descriptions with the correct type of binary star.
Visual binary- two seperate stars are seen Stars orbits can be seen Spectroscopic binary- Light of two stars seen as single blob detected by Doppler shift of emission/absorption lines
Select all the spectral properties that vary with temperature.
Which lines are visible The depth, or darkness, of spectral lines
An arc minute is ________. (Select all that apply.)
a unit of angular size 1/60 of a degree
An astronomer who records a visible light spectrum of a star will normally find it is a(n) ____.
absorption-line spectrum
Paired stars in gravitational orbit around each other are called
binary stars
A spectrum of a glowing object such as a star ________. (Select all that apply.)
can be used to determine the elements present in the object is a measurement of the amount of light, emitted as a function of wavelength shows effects dependent on the surface temperature of the object
The larger the value you measure for the parallax of a star, the ____ the star is.
closer
To use the method of standard candles, it is first necessary that astronomers ________. (Select all that apply.)
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
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
The plot shown in the image is an example of a(n) ____.
light curve
A bright star will have a ____ number for its apparent magnitude than a dimmer star.
lower
In the H-R diagram, the vertical axis is ____ and the horizontal axis is ____.
luminosity; surface temperature
The diagonal line of stars indicated by the arrows in the diagram is the ____.
main sequence
In a binary star system, the period of each star's orbit ____.
must be the same
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 ____.
of diffraction and resolution effects in the camera
Select (two) answers to complete the two sentences: Our brains estimate the distance to objects by using the method of ____. The baseline is the distance ____.
parallax between our eyes
Looking a pictures of the sky, you notice that over the course of two years, the position of a particular star compared to the background stars shifts several arcminutes. The motion is in a straight line. What is the name astronomers use for such motion?
proper motion
Match the methods of direct stellar radius measurements with their descriptions.
space telescopes- Avoids blurring by the atmosphere Speckle interferometry- Uses a large telescope with a high-speed camera Interferometry- Combines observations from multiple small telescope.
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 binary eclipsing binary
You determine through spectroscopy that two stars are both a specific kind of standard candle. If the brightness of star A is 100 times the brightness of star B, then ____.
star B is 10 times farther away
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 ____.
star Gamma is half as far away
Match the times indicated with the measurements that can be made and the description of the configuration of a pair of binary stars.
t1- diameter of the larger star, hot star in front of cool one t2- diameter of the smaller star t3- cool star in front of hot one
The Stefan-Boltzmann law tells us that for two stars of the same size, the more luminous one has a higher ____.
temperature
To use the modified form of Kepler's third law to determine the sum of the masses of a pair of stars, astronomers need to measure or know ____. (Select all that are needed.)
the semimajor axis of the orbit the orbital period
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 = a3P2a3P2, the mass you will find will be ____. (Select all that apply.)
the sum of both stars' masses in solar masses (M☉)
Select two answers to fill in the blanks: At the highest surface temperature of stars, you expect the Balmer absorption lines in stellar spectra to become ____ because most of the electrons are already ____.
weaker, above the n = 2 orbital
If star A is moving at a radial velocity of +600 km/sec and star B is moving at +100 km/sec, then how is the change in λ (written Δλ) for A different than for B?
Δλ for A is 6 times bigger than for B.
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 km/sec
