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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Which of the following is a technique that can be used to speed up a spacecraft without the need for extra fuel?
A) a gravitational slingshot, in which the spacecraft gains momentum by flying near a planet B) releasing unnecessary weight after takeoff to make the spacecraft lighter C) flattening after takeoff to make the spacecraft more aerodynamic D) landing on a fast-moving asteroid and relaunching at high speed E) collect material in space that can power the spacecraft
Stars are continually forming in the halo of our Galaxy today
Indicate whether the statement is true or false
A flashlight beam is seen because of
a. specular reflection. b. diffuse reflection. c. dispersion. d. refraction.
What is the temperature of a system in thermal equilibrium with another system made up of ice and water at one atmosphere of pressure?
a. 0°F c. 0 K b. 273 K d. 100°C