13. The center of the disk of the visible Sun appears brighter than the edges because we see
14. Which of the following objects is NOT an endpoint of a star's evolutionary life?
15. In the process of helium shell fusion in low-mass stars near the end of their lives, the star moves upward and to the right as a red giant in the Hertzsprung-Russell diagram. In this process, the star is
A) contracting, becoming hotter, and becoming much less luminous. B) expanding, cooling, and becoming more luminous. C) expanding, heating up, and becoming more luminous. D) contracting, cooling, and hence becoming less luminous.
16. The neutrino is
17. In which of the following parameters does a photon of blue light NOT differ from a photon of yellow light, in a vacuum?
18. Pulsars, emitting very regular radio and sometimes visible light pulses, are what type of object?