The hydrogen lines in spectral type A stars
a. are most narrow for supergiants.
b. are most narrow for main-sequence stars.
c. can not be used to estimate the luminosity of the star.
d. are very weak and difficult to see.
e. are useful in determining the apparent magnitude of the star.
a
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Indicate whether the statement is true or false
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a. specular reflection. b. diffuse reflection. c. dispersion. d. refraction.
Which of the following is a technique that can be used to speed up a spacecraft without the need for extra fuel?
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