Astronomy Module 12
Stars A and B have equal brightness, but star B is eight times as far from Earth as star A. How much more luminous is star A than star B?
1/64
Star A's spectrum is most intense at 500 nm, while star B's spectrum is most intense at 750 nm. If star A has a temperature of 5,800 K, what is the temperature of star B?
3,850 K
Sort the following statements by the type of binary system they describe.
Astrometric: two separate stars are seen in an image binary orbit may be viewed nearly face-on Spectroscopic: looks like one constant-brightness star relies on the Doppler effect Eclipsing: binary orbit must be seen nearly edge-on brightness changes repeatedly over time
About 90% of stars observed fall on the main sequence (or MS) on the HR diagram extending from the upper left to lower right of the diagram. The main-sequence portion of the HR diagram is unobscured in the figure. Match the properties to the stars.
Hot End: most-luminous stars most-massive stars shortest lifetime Cool End: longest lifetime least-massive stars
Sort the following properties of stars by whether they can be measured through imaging (taking pictures through a telescope and measuring them) or spectroscopy.
Imaging: luminosity (if distance is known) distance (using stellar parallax) proper motion distance (using Cepheid variables) Spectroscopy: radial velocity chemical composition Either: temperature determining if a star is in a binary system
Which of the following correctly orders the spectral types of stars from coolest to hottest?
MKGFABO
Sort the main-sequence stars in the table below into the correct spectral type given the information in the table. Star Mass (M⊙) Radius (R⊙) Temperature(K) Dasher 2.5 1.9 ? Dancer ? 4.5 17,000 Prancer 65 ? ? Vixen ? ? 6,500 Comet ? 0.6 ? Cupid 0.99 ? ? Donner ? 10 ? Blitzen ? ? 3,000
O: Prancer Donner B: Dancer A: Dasher F: Vixen G: Cupid K: Comet M: Blitzen
How would parallax measurements of stars made from Jupiter differ from those made from Earth?
Parallax for a given star would be greater.
Rank the following steps in the distance ladder from the smallest to largest distances being measured.
Shortest Distances measuring 1 AU (the size of Earth's orbit) using radar and Kepler's laws stellar parallax using Cepheid variables as standard candles using supernova explosion as standard candles in distant galaxies Longest Distances
Choose the statement about variable stars that is not true.
Their luminosity may be continually increasing.
Two neighboring stars are seen with significant differences in composition. What is not likely to be true of these stars?
They were born together.
Label the locations of the stars on the HR diagram.
Top Left: main-sequence star with surface temperature 30,000K Top Middle: blue giant: blue and much larger than the Sun Top Right: red giant: red and much larger than the Sun Upper Middle: main-sequence star almost a thousand times as bright as the Sun Lower Middle: the Sun Bottom Left: white dwarf: very hot and very small Bottom Right: K-type main-sequence star
While the HR diagram is a plot of the temperatures of stars versus their luminosities, other stellar properties vary with location along the HR diagram. Examine the diameters and lifetimes of stars in different locations, and then label the locations on the HR diagram for the stars indicated.
Top left: shortest-lifetime stars Top right: largest-diameter stars Bottom right: longest-lifetime stars
What is the definition of a standard candle?
an object whose luminosity is known without needing to know its distance
What quantities must be measured in order to calculate the luminosity of a star?
brightness and distance
Massive stars:
burn their fuel rapidly, so they have shorter lifetimes than low-mass stars.
How have astronomers learned about the life cycles of stars?
by measuring the properties of many stars at a single instant
What property of a star can best be used to determine its temperature?
color
Which of the following is a relational property of stars?
distance
Wien's law tells us that
in blackbodies, temperature and peak radiation wavelength (color) are related.
A star's position on the main sequence does not tell us
its chemical composition.
What determines the location of a star on the main sequence?
mass
Which of the following quantities is NOT necessary to observe in order to construct an HR diagram of a system of stars?
mass of each star
On the main sequence, a star's spectral type is ultimately determined by its:
mass.
What properties of Cepheid variable stars are most often measured to determine their distance?
period and brightness
On an HR diagram, the star Mira appears directly below the star Betelgeuse. Compared to Betelgeuse, Mira has a:
smaller radius.
What causes a star to leave the main sequence?
the consumption of the stellar core's hydrogen
What does the main sequence show?
the distribution of core hydrogen-fusing stars by mass
What was Henrietta Leavitt's most important contribution to astronomy?
the period-luminosity relation of Cepheid variables
What does the HR diagram of a cluster not tell astronomers?
the rotation of the cluster
