Question 1

A particular star appears brighter seen through a blue filter than seen through a yellow filter.Which surface temperature is possible for this star? (See Figure 10-4,Comins,Discovering the Essential Universe,6th ed.)
A) 3000 K
B) 12,000 K
C) 4500 K
D) 6000 K

Accepted Answer

This is because hotter stars emit more blue light (shorter wavelengths) compared to cooler stars which emit more red light (longer wavelengths). Therefore a star appearing brighter through a blue filter than through a yellow filter indicates that it emits more blue light, which is characteristic of hotter stars.

Question 2

A red filter passes light at the long-wavelength end of the visible spectrum as shown,for example,in Figure 10-4 in Comins,Discovering the Essential Universe,6th ed.Star 1 and star 2 are viewed through identical red filters,and star 1 appears brighter than star 2 through the filter.What can be determined from this information?
A) Star 1 is hotter than star 2.
B) Star 2 is hotter than star 1.
C) Star 1 is more luminous than star 2.
D) Nothing can be concluded from this fact alone.

Accepted Answer

The answer of A red filter passes light at the...

Question 3

Why does the star Bellatrix in Orion looks bluish to the naked eye?
A) The spectrum of light emitted from Bellatrix peaks in the blue region of the spectrum, and in fact, almost all its light is concentrated in the blue region of the spectrum.
B) The spectrum of light emitted from Bellatrix peaks in the ultraviolet region of the spectrum. Within the visible part of the spectrum, there is more emission in the blue than in any other color.
C) Bellatrix is moving toward Earth rapidly enough that its light appears appreciably blueshifted.
D) Bellatrix is made of blue material.

Accepted Answer

Bellatrix emits more light in the ultraviolet region, and within the visible spectrum, it emits more blue light, making it appear bluish.

Question 4

The star Regulus,in the constellation Leo,appears brighter through a blue filter than it does through a yellow filter.Suppose that a second star is found that has the same brightness as Regulus through the blue filter but is brighter than Regulus through the yellow filter.From this information,we can say conclusively that the second star has:
A) a higher temperature.
B) the same temperature but a higher luminosity.
C) the same temperature but a lower luminosity.
D) a lower temperature.

Accepted Answer

The second star being brighter through the yellow filter suggests it emits more light at longer wavelengths, which is characteristic of a cooler star. Hence, it likely has a lower temperature than Regulus.

Question 5

Rigel,the bright star in the knee of Orion,has a surface temperature of about 12,000 K.Through which filter will it appear brightest? (See Figure 10-4,Comins,Discovering the Essential Universe,6th ed.)
A) ultraviolet
B) blue
C) yellow
D) red

Accepted Answer

Rigel's temperature is much hotter than the temperature of the sun (around 5,500 K), which means that its peak radiation will be at shorter wavelengths. The peak of its black-body spectrum is actually in the ultraviolet region, which means it will appear brightest through an ultraviolet filter.

Question 6

Which two fundamental parameters are MOST often used to place a particular star on a path of stellar evolution for comparison with theoretical models?
A) apparent magnitude and distance
B) apparent magnitude and temperature
C) luminosity, or total energy output, and distance
D) luminosity, or total energy output, and temperature

Accepted Answer

The two fundamental parameters that are most often used to place a particular star on a path of stellar evolution for comparison with theoretical models are luminosity, or total energy output, and temperature. These parameters provide crucial information about the internal structure and behavior of stars, and are essential for understanding how they evolve over time. Apparent magnitude and distance are important for determining a star's brightness and location, respectively, but do not provide as much insight into its evolutionary path.

Question 7

The Sun's spectrum peaks in the green region (i.e.,green is the most intense color in its spectrum).The spectrum of Rigel (the knee of Orion)peaks in the short-wavelength end of the visible spectrum.Compared with the Sun,Rigel is:
A) cooler and redder.
B) hotter and redder.
C) cooler and whiter.
D) hotter and whiter.

Accepted Answer

Since Rigel's spectrum peaks in the short-wavelength end of the visible spectrum, it has hotter temperatures than the Sun. Additionally, since it peaks in the blue/white end of the spectrum, it is whiter in color compared to the Sun's green peak.

Question 8

An astronomer is measuring the brightness of a particular star through a telescope,using different filters in the visual (yellow-green),violet,and ultraviolet regions.What is the name of the technique being used by this astronomer?
A) spectroscopy
B) geometry
C) interferometry
D) photometry

Accepted Answer

The technique being used by the astronomer is photometry, which involves measuring the brightness of an object in different colors or wavelengths of light. Spectroscopy involves analyzing the spectrum of light from an object to determine its composition and other properties, while interferometry involves combining light from multiple telescopes to improve resolution. Geometry is a mathematical tool used to calculate the positions and distances of objects in space.

Question 9

A particular star appears fainter seen through a blue filter than seen through a yellow filter.Which surface temperature is possible for this star? (See Figure 10-4,Comins,Discovering the Essential Universe,6th ed.)
A) 12,500 K
B) 38,000 K
C) 8800 K
D) 3800 K

Accepted Answer

A star appearing fainter through a blue filter than a yellow filter suggests it emits less blue light, indicating a cooler surface temperature. 3800 K is consistent with a cooler star, which emits more light in the red/yellow spectrum than in the blue.

Question 10

The technique called photometry in stellar astronomy is the measurement of the:
A) arrival times of photons from variable and pulsating stars to determine accurately the pulsation or rotation periods of these stars.
B) intensity of light from stars through several limited-bandpass filters from which surface temperature, variability, luminosity, and so on of stars can be determined.
C) relative absorption of light by different atoms and molecules in high-resolution spectra of starlight, from which stellar temperatures can be estimated.
D) precise positions and relative motions of stars in the Galaxy, from which galactic structure and overall rotation can be determined.

Accepted Answer

Photometry is the measurement of the intensity of light from stars. Through the use of limited-bandpass filters, several properties of stars, such as surface temperature, luminosity, and variability, can be determined. Option A describes a technique called timing, option C describes spectroscopy, and option D describes astrometry.

Question 11

A particular star appears approximately equally bright when viewed through a blue filter and through a yellow filter.What is the approximate surface temperature of this star? (See Figure 10-4,Comins,Discovering the Essential Universe,6th ed.)
A) 6000 K
B) 12,000 K
C) 3000 K
D) It is not possible for a star to be equally bright at two different wavelengths.

Accepted Answer

The star's surface temperature is approximately 6000 K, as this temperature corresponds to a peak in the star's spectrum that would make it appear equally bright through both blue and yellow filters.

Question 12

The star Rigel,in the constellation Orion,appears brighter through a blue filter than it does through a yellow filter.Suppose that a second star is found that has the same brightness as Rigel through the yellow filter but is brighter than Rigel through the blue filter.From this information,we can say conclusively that the second star has:
A) the same temperature but a lower luminosity.
B) a higher temperature.
C) a lower temperature.
D) the same temperature but a higher luminosity.

Accepted Answer

The fact that the second star appears brighter through the blue filter than Rigel, but has the same brightness as Rigel through the yellow filter, suggests that the second star emits a larger proportion of its light at shorter wavelengths (blue light) compared to Rigel. This implies that the second star has a higher temperature than Rigel. Additionally, we cannot determine the luminosity of the second star based on the given information.

Question 13

For Balmer series lines to show up strongly in absorption in stellar spectra,significant numbers of hydrogen atoms have to have electrons in the n = 2 energy level.What then does the appearance of these lines in a stellar spectrum tell us about the temperature of the star's surface?
A) The appearance of the lines tells us very little about the temperature because hydrogen gas will show significant Balmer absorption, whatever the surface temperature.
B) The temperature must be high enough to ionize the hydrogen atoms by collision in order that they can absorb from this level.
C) The temperature must be reasonably low so that no atoms will have electrons excited beyond this energy level (e.g., to n = 3).
D) The temperature must be reasonably high to excite the electrons to this level by collisions, but not high enough to ionize the atoms.

Accepted Answer

The appearance of Balmer series lines in a stellar spectrum tells us that the temperature of the star's surface is reasonably high enough to excite the electrons of hydrogen atoms to the n = 2 level by collisions, but not high enough to ionize the atoms. If the temperature was too low, then the electrons wouldn't be excited beyond the n = 1 level, and if the temperature was too high, then the atoms would be completely ionized, and no absorption lines would be visible. Therefore, the appearance of Balmer series lines can give us an estimate of the temperature of the star's photosphere, which is the layer of the atmosphere that emits most of its visible light.

Question 14

The difference in the brightness of a star as seen through two different colored filters,for example,blue and yellow,is directly related to which stellar property?
A) distance from Earth
B) luminosity
C) surface temperature
D) radius

Accepted Answer

The brightness difference between two colored filters is related to the star's surface temperature. Blue filters are more sensitive to hotter temperatures, while yellow filters are more sensitive to cooler temperatures. Therefore, if the star appears brighter in the blue filter than in the yellow filter, it indicates that the star has a higher surface temperature.

Question 15

Why is there a limited range of stellar surface temperatures around 10,000 K at which neutral hydrogen gas absorbs visible light in the Balmer series?
A) There must be electrons at the n = 3 energy level for Balmer absorption to occur. If the gas is too cold, electrons are only in the n = 1 and 2 levels; if the gas is too hot, the gas is ionized and no electrons are left in the hydrogen atoms.
B) Electrons in hydrogen have to be at the n = 2 energy level to produce absorption in this series. If the gas is too cold, most atoms are in the n = 1 state; if it is too hot, most atoms are ionized.
C) Electrons must be in the ground state n = 1 to undergo Balmer absorption. If the gas is too cold, electrons cannot be excited from this level; if the gas is too hot, there are no electrons left in the n = 1 level.
D) There must be sufficient continuum radiation from the stellar surface in the visible region to be absorbed by the hydrogen gas.

Accepted Answer

The Balmer series of hydrogen absorption lines only occurs when electrons are at the n = 2 energy level. If the gas is too cold, most atoms are in the n = 1 state and cannot produce absorption; if it is too hot, most atoms are ionized and cannot produce absorption. Therefore, there is a limited range of temperatures around 10,000 K at which the Balmer series can be observed.

Question 16

A star has a surface temperature of 6000K (see Figure 10-4b,Comins,Discovering the Essential Universe,6th ed.).Its spectrum registers a certain intensity in the green middle of the visible spectrum.Which statement characterizes the rest of the spectrum?
A) The violet is brighter than the green, but the red is less intense.
B) The violet is less intense than the green, but the red is more intense.
C) The violet and the red are both less intense than the green.
D) The violet and the red are both more intense than the green.

Accepted Answer

A star with a surface temperature of 6000K emits most of its light in the visible spectrum, peaking around the green. According to Wien's Law, the intensity decreases on either side of the peak, making both violet and red less intense than green.

Question 17

Optical glass filters are used to select certain portions of a star's light for photometry.Which filter would MOST closely match the sensitivity of our eyes,which have a peak sensitivity at about 550 nm wavelength? (See Figure 3-1,Comins,Discovering the Essential Universe,6th ed.)
A) ultraviolet
B) red
C) yellow
D) blue

Accepted Answer

The peak sensitivity of our eyes is around 550 nm, which corresponds to the yellow-green part of the spectrum. Therefore, a filter that matches this wavelength range would be the best choice. The yellow filter is the one that comes closest to matching the sensitivity of our eyes.

Question 18

When observed through a set of photometric filters,a distant star is seen to be brightest through the ultraviolet filter,less bright through the blue filter,and faintest through the yellow filter.What conclusion can be drawn from this information,assuming no absorption of light between the star and Earth?
A) The question gives insufficient information to draw a conclusion about a star's surface temperature.
B) The star has an intermediate temperature close to that of the Sun.
C) The star has a very high surface temperature.
D) The star has a very low surface temperature.

Accepted Answer

The fact that the star is brightest through the ultraviolet filter and less bright through the blue and yellow filters indicates that the star is emitting a significant amount of energy at high frequencies, consistent with a very high surface temperature.

Question 19

If a certain star shows a strong absorption spectrum in hydrogen Balmer lines,the surface temperature of the star is hot enough that collisions between atoms there:
A) ionize virtually all of the hydrogen atoms.
B) promote electrons in many hydrogen atoms to the n = 2 energy level.
C) promote electrons in many hydrogen atoms to the n = 3 energy level.
D) convert many helium atoms to hydrogen atoms.

Accepted Answer

The hydrogen Balmer lines are produced when electrons in hydrogen atoms undergo transitions from higher energy levels to the n = 2 energy level. The fact that a strong absorption spectrum is seen in these lines indicates that there are many hydrogen atoms present in the outer layers of the star and that collisions are occurring that are exciting electrons to this level. However, the temperature is likely not hot enough to ionize all of the hydrogen atoms, and the n = 3 energy level is less likely to be populated than the n = 2 level. Helium is not converted into hydrogen during collisions, as they are two different elements.

Question 20

Development of the Henry Draper Catalog of stellar classifications was begun in the late nineteenth century.The catalog originally classified stars according to the strengths of their hydrogen lines.By the 1920s,however,the sequence had been reorganized so that the stars were classified by surface temperature.What important scientific development made possible this reinterpretation?
A) the discovery of nuclear physics and how stars generate their energy
B) the discovery of blackbody radiation and the blackbody curve
C) the development of atomic physics and how atoms emit light
D) the development of radio astronomy and the detection of molecules in space

Accepted Answer

The development of atomic physics and understanding of how atoms emit light allowed scientists to classify stars based on their surface temperature, as it explained the relationship between temperature and spectral lines.

Quiz 10: Characterizing Stars

A particular star appears brighter seen through a blue filter than seen through a yellow filter.Which surface temperature is possible for this star? (See Figure 10-4,Comins,Discovering the Essential Universe,6th ed.)

Why does the star Bellatrix in Orion looks bluish to the naked eye?

Rigel,the bright star in the knee of Orion,has a surface temperature of about 12,000 K.Through which filter will it appear brightest? (See Figure 10-4,Comins,Discovering the Essential Universe,6th ed.)

Which two fundamental parameters are MOST often used to place a particular star on a path of stellar evolution for comparison with theoretical models?

The Sun's spectrum peaks in the green region (i.e.,green is the most intense color in its spectrum) .The spectrum of Rigel (the knee of Orion) peaks in the short-wavelength end of the visible spectrum.Compared with the Sun,Rigel is:

An astronomer is measuring the brightness of a particular star through a telescope,using different filters in the visual (yellow-green) ,violet,and ultraviolet regions.What is the name of the technique being used by this astronomer?

A particular star appears fainter seen through a blue filter than seen through a yellow filter.Which surface temperature is possible for this star? (See Figure 10-4,Comins,Discovering the Essential Universe,6th ed.)

The technique called photometry in stellar astronomy is the measurement of the:

A particular star appears approximately equally bright when viewed through a blue filter and through a yellow filter.What is the approximate surface temperature of this star? (See Figure 10-4,Comins,Discovering the Essential Universe,6th ed.)

For Balmer series lines to show up strongly in absorption in stellar spectra,significant numbers of hydrogen atoms have to have electrons in the n = 2 energy level.What then does the appearance of these lines in a stellar spectrum tell us about the temperature of the star's surface?

The difference in the brightness of a star as seen through two different colored filters,for example,blue and yellow,is directly related to which stellar property?

Why is there a limited range of stellar surface temperatures around 10,000 K at which neutral hydrogen gas absorbs visible light in the Balmer series?

A star has a surface temperature of 6000K (see Figure 10-4b,Comins,Discovering the Essential Universe,6th ed.) .Its spectrum registers a certain intensity in the green middle of the visible spectrum.Which statement characterizes the rest of the spectrum?

Optical glass filters are used to select certain portions of a star's light for photometry.Which filter would MOST closely match the sensitivity of our eyes,which have a peak sensitivity at about 550 nm wavelength? (See Figure 3-1,Comins,Discovering the Essential Universe,6th ed.)

If a certain star shows a strong absorption spectrum in hydrogen Balmer lines,the surface temperature of the star is hot enough that collisions between atoms there: