How have Hubble images revised our view of the structure of planetary nebulae, and even the potential for the Sun to become one?
What will be an ideal response?
Instead of just spherical shells, we know that many if not most planetary nebulae are bipolar ejections; often the appearance of a "ring" comes from the dual lobes coming directly at us and away from us. The intricate structure suggests that magnetic fields are molding the nebulae, and that perhaps the rotation and perturbation of a companion star may be often involved. It may be that only binary stars can produce these spectacular stellar shrouds.
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Physically, why is a gas molecule’s speed v more likely to be near vp than near zero?
A. There are fewer quantum states with smaller speeds than larger speeds.
B. The Boltzmann factor has a larger value near v = vp than near v = 0.
C. We know that 
A particle moving along the x axis has a position given by x = 54t? 2.0t3 m. At the time t = 3.0 s, the speed of the particle is zero. Which statement is correct?
A. The particle remains at rest after t = 3.0 s. B. The particle no longer accelerates after t = 3.0 s. C. The particle can be found at positions x< 0 m only when t< 0 s. D. All of the above are correct. E. None of the above is correct.
The presence of vesicular basalts among the lunar rock samples shows that
a. the lunar surface was fragmented by meteorite impacts. b. volcanism did not occur on the moon. c. the crust must have been made of anorthosite. d. molten lava once flowed over the lunar surface. e. the moon was once hit by a very large meteorite.
Quasar spectra often show many absorption lines that all appear to be due to the same electron transition (such as level 1 to level 2 in hydrogen) but that fall at different wavelengths in the spectrum. Why do we think this is the case?
A) We are seeing absorption lines from clouds of gas that lie between us and the quasar, and therefore each cloud has a different redshift. B) Quasars are rotating rapidly, and this rotation produces spectral lines with a wide variety of Doppler shifts. C) The lines fall at different wavelengths because they are produced by different chemical elements. D) No one knows—it remains perhaps the greatest mystery about quasars.