ASTR 1010 / Astronomy 1010 Final HW Complete
Questions & Answers.
One of the most important earlier steps in understanding stars was to group them
into classes called spectral types that could offer clues as to why they are
different from one another. Shown here are spectra of some main-sequence stars.
Before stars were very well understood, they were classified into an order that
was based on the relative strength of hydrogen absorption lines, marked by
arrows the image shown.
Look at the spectra for stars of different spectral type. Choose the list of spectral
types that are in order of decreasing strength of their hydrogen lines, as indicated
by the arrows (strongest absorption first, weakest last).
A0, B0, F0, G0, K0
Measurements of various properties of stars allowed astronomers to determine a
more physically meaningful way of ordering the different spectral types than just
by the strength of their hydrogen absorption lines.
Study this table of properties, and use it to determine how the stars should be
ordered. Click on the spectrum for each spectral type in order of decreasing
strength of whatever property or properties you choose to use from the table.
top to bottom
c, b, d, e, f, g, a
Hertzsprung and Russell were the first to plot stellar luminosities as a function of
their spectral type. When placed in the OBAFGKM order, an interesting pattern
emerged.
The following figure shows one of these plots, named a Hertzsprung-Russell, or
H-R, diagram after its founders. Each dot represents a single star, with green,
yellow, and red dots simply indicating regions where there are a larger number of
stars in that part of the plot. The color of the stars is roughly given by the vertical
colored bands in the plot background.
-Redder main-sequence stars are fainter on average than bluer main-sequence stars.
-The spectral type of a star uniquely determines its color.
The spectral type of a star is directly related to its color. Recall that a star emits
light as a blackbody, which has a particular shape to its spectrum, as shown in
this figure.
Based on this, what basic property of a star determines its color (and thus its
spectral type)?
temperature
The majority of stars, including the Sun, are on the main sequence. The masses
and sizes of main-sequence stars in the H-R diagram are indicated in this figure.
Study how the various properties of a main-sequence star are related to one
another in the figure. Then select the properties in the list that would increase if
the mass of a main-sequence star is increased.
, -temperature
-luminosity
-radius
Spectral type correlates directly with the temperature of the star. This is not
enough to completely classify stars, however, because the luminosity of a star,
and thus its exact position on the H-R diagram, depends on something else in
addition to temperature. This is apparent from the H-R diagram because of the
different populations of stars that exist in addition to the main sequence—they
may have the same temperature as a main-sequence star, but a completely
different luminosity
Based on the figure, what other property can we use to further classify stars?
radius
A star can be fully classified with two descriptors: its spectral type (determined
by temperature) and its luminosity class (determined by size). These two together
give the location of the star on the H-R diagram, and all other basic properties
(except composition) follow from that. Luminosity classes are given by roman
numerals I through V, plus WD. The locations of these classes are shown in the
figure here, along with the terms describing what type of stars they are (i.e., main
sequence, supergiant, etc.).
Based on this figure, rank the following luminosity classes in order of increasing
size.
smallest largest
WD
V
IV
III
II
I
Based on its position in this H-R diagram, which of the following best describes
the complete classification of the Sun?
Note: The numbers after the letter for each spectral type run from 0 through 9 for
each type (e.g., the following would read from left to right on the diagram: O0
through O9, then B0 through B9, etc.).
G2 V
Both spectral type and luminosity class are needed to determine roughly where
any particular star will lie on the H-R diagram. In this diagram, label where a K5 I
star and a K5 V star might be located.
k5 I star- k5 104
k5 V star- k5 10-1
Which of the following statements is true, based on the position of the stars in
this H-R diagram?
A K5 I star has a larger radius than a K5 V.
When observed from two widely separated locations, an object appears to move
_____ against the background than when observed from two locations near one
another.
Questions & Answers.
One of the most important earlier steps in understanding stars was to group them
into classes called spectral types that could offer clues as to why they are
different from one another. Shown here are spectra of some main-sequence stars.
Before stars were very well understood, they were classified into an order that
was based on the relative strength of hydrogen absorption lines, marked by
arrows the image shown.
Look at the spectra for stars of different spectral type. Choose the list of spectral
types that are in order of decreasing strength of their hydrogen lines, as indicated
by the arrows (strongest absorption first, weakest last).
A0, B0, F0, G0, K0
Measurements of various properties of stars allowed astronomers to determine a
more physically meaningful way of ordering the different spectral types than just
by the strength of their hydrogen absorption lines.
Study this table of properties, and use it to determine how the stars should be
ordered. Click on the spectrum for each spectral type in order of decreasing
strength of whatever property or properties you choose to use from the table.
top to bottom
c, b, d, e, f, g, a
Hertzsprung and Russell were the first to plot stellar luminosities as a function of
their spectral type. When placed in the OBAFGKM order, an interesting pattern
emerged.
The following figure shows one of these plots, named a Hertzsprung-Russell, or
H-R, diagram after its founders. Each dot represents a single star, with green,
yellow, and red dots simply indicating regions where there are a larger number of
stars in that part of the plot. The color of the stars is roughly given by the vertical
colored bands in the plot background.
-Redder main-sequence stars are fainter on average than bluer main-sequence stars.
-The spectral type of a star uniquely determines its color.
The spectral type of a star is directly related to its color. Recall that a star emits
light as a blackbody, which has a particular shape to its spectrum, as shown in
this figure.
Based on this, what basic property of a star determines its color (and thus its
spectral type)?
temperature
The majority of stars, including the Sun, are on the main sequence. The masses
and sizes of main-sequence stars in the H-R diagram are indicated in this figure.
Study how the various properties of a main-sequence star are related to one
another in the figure. Then select the properties in the list that would increase if
the mass of a main-sequence star is increased.
, -temperature
-luminosity
-radius
Spectral type correlates directly with the temperature of the star. This is not
enough to completely classify stars, however, because the luminosity of a star,
and thus its exact position on the H-R diagram, depends on something else in
addition to temperature. This is apparent from the H-R diagram because of the
different populations of stars that exist in addition to the main sequence—they
may have the same temperature as a main-sequence star, but a completely
different luminosity
Based on the figure, what other property can we use to further classify stars?
radius
A star can be fully classified with two descriptors: its spectral type (determined
by temperature) and its luminosity class (determined by size). These two together
give the location of the star on the H-R diagram, and all other basic properties
(except composition) follow from that. Luminosity classes are given by roman
numerals I through V, plus WD. The locations of these classes are shown in the
figure here, along with the terms describing what type of stars they are (i.e., main
sequence, supergiant, etc.).
Based on this figure, rank the following luminosity classes in order of increasing
size.
smallest largest
WD
V
IV
III
II
I
Based on its position in this H-R diagram, which of the following best describes
the complete classification of the Sun?
Note: The numbers after the letter for each spectral type run from 0 through 9 for
each type (e.g., the following would read from left to right on the diagram: O0
through O9, then B0 through B9, etc.).
G2 V
Both spectral type and luminosity class are needed to determine roughly where
any particular star will lie on the H-R diagram. In this diagram, label where a K5 I
star and a K5 V star might be located.
k5 I star- k5 104
k5 V star- k5 10-1
Which of the following statements is true, based on the position of the stars in
this H-R diagram?
A K5 I star has a larger radius than a K5 V.
When observed from two widely separated locations, an object appears to move
_____ against the background than when observed from two locations near one
another.
