The Sun's photosphere is, by mass, about 75%
a. helium.
b. carbon.
c. hydrogen.
d. oxygen.
c
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In the Czochralski technique of single-crystal growth, the crystal growth is initiated by epitaxial attachment of atoms to a(n) ___________crystal.
Fill in the blank(s) with the appropriate word(s).
Time Dilation: A spaceship visits a star that is 4.5 light-years from Earth, and the spaceship travels at one-half the speed of light for the entire trip.(a) How long did the trip take according to an observer on Earth?(b) How long did the trip take according to an observer on the spaceship?
What will be an ideal response?
Suppose you use the Southern Cross to determine that the south celestial pole appears 40 degrees above your horizon. Then you must be located at
A) latitude 40 degrees north. B) latitude 50 degrees south. C) latitude 40 degrees south. D) longitude 40 degrees.
If the density of the Universe is less than the critical density, then
A. the Universal expansion will eventually stop sometime in the future. B. the Universe will eventually stop expanding, and then begin to collapse until it ends in a Big Crunch. C. the Universe will not change because its evolution does not depend on the critical density. D. the Universe will expand forever.