chapter 2 Flashcards
What is a dwarf star?
main-sequence star
What is a white dwarf star?
star of about the same size (diameter) as Earth
compositions of white dwarfs
carbon and oxigen
nova
binary star
binary stars are made of
white dwarf and another dead star
How far away is the nearest star beyond the Sun?
about 4 ly away
What is parallax?
apparent shift in position of an object as the observer moves
The motion that is used to change the position of the observer in the most common parallax measurements of distances to relatively nearby stars is the
motion of Earth in its orbit around the Sun.
Stellar parallax appears because
Earth moves in space.
Apparent magnitude is a measure of a star’s
brightness, as seen from Earth.
A star of apparent magnitude +1 appears _____ than a star of apparent magnitude +2.
brighter
The statement that the apparent magnitude of a variable star has increased indicates that its
brightness has decreased
Luminosity is measured in
watts
The luminosity of a star is
its total energy output into all space
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?
photometry
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 temperature must be reasonably high to excite the electrons to this level by collisions but not high enough to ionize the atoms.
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?
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
The chemical makeup of the Sun’s surface can be determined by
solar spectroscopy.
Which of the following spectral classification letters signifies the hottest stellar surface temperature?
B
Which of the following four spectral classifications signifies the coolest stellar surface temperature?
K
The Hertzsprung-Russell diagram is a plot of
absolute magnitude (or intrinsic brightness) against temperature of a group of stars
If you compare two stars, the one with the _____ must have the greater luminosity.
smaller absolute magnitude
What are the two physical parameters of stars that are plotted in the Hertzsprung-Russell diagram?
luminosity and surface temperature
Compared with a star in the middle of the Hertzsprung-Russell diagram, a star in the lower left of the diagram is
smaller
Compared with a star in the middle of the Hertzsprung-Russell diagram, a star in the upper right of the diagram is
larger.
