Each dot on this graph represents an individual Cepheid variable star. Which of the following is true for a Cepheid that is 10,000 times as luminous as the Sun?
A) It varies gradually in brightness, with a peak in brightness about every 30 days.
B) It orbits the center of the galaxy about every 30 days.
C) It orbits its binary companion about every 30 days.
D) It undergoes a massive flare about every 30 days.
A) It varies gradually in brightness, with a peak in brightness about every 30 days.
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Atomic Nucleus: The symbol for a certain isotope of strontium is 
Sr. What is the mass number of this isotope?
A. 38 B. 52 C. 88 D. 90 E. 128
When the outer envelope of a red giant is ejected, the remaining exposed core of a low mass star is called a
A. black hole. B. white dwarf. C. neutron star. D. red super giant.
Typical stellar spectra appear as:
A) a series of bright, colored lines. B) an unbroken rainbow of colors. C) a rainbow, but with some dark lines mixed in. D) a rainbow with some bright lines on top of the continuum. E) a very redshifted rainbow due to the expansion of the universe.
An alloy of 73.9 atomic % tin (Sn) and 26.1 atomic % lead (Pb) is mixed and heated to 250°C. See the lead tin phase diagram in Figure 5.11a.
(a) At 250°C what phases are present, what are their chemical compositions, and what is the atom fraction of each phase?
(b) This Pb-Sn mixture is then cooled to room temperature (25°C). What phases are present, what are their chemical compositions, and what is the atom fraction of each phase present?
