Sunspots are dark because
a. regions of the photosphere are obscured by material in the chromosphere.
b. shock waves move through the photosphere.
c. the sun rotates differentially.
d. the strong magnetic field inhibits the currents of hot gas rising from below.
e. they radiate their energy into space faster than the rest of the photosphere.
D
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For a high-temperature gas turbine application, you have chosen to use alumina ceramic material for a non-rotating part that is subject to modest forces. You find that you can save a significant amount of money by buying alumina that is of 1% lower density than more-expensive alumina, and in aircraft design saving weight is always desired. What aspect of the defect structure of the cheaper alumina should you investigate to determine its possible effects on mechanical properties, and why may this be important?
What will be an ideal response?
Which of the following are found on Triton?
a. craters b. flooded basins c. atmospheric clouds d. a thick nitrogen atmosphere e. craters, flooded basins, atmospheric clouds, and a thick nitrogen atmosphere
This figure shows the Cepheid period-luminosity relation. What is the approximate luminosity of a Cepheid star that varies in brightness with a period of 10 days?
A) about 1000 times the luminosity of the Sun B) about 3000 times the luminosity of the Sun C) about 10,000 times the luminosity of the Sun D) about 30,000 times the luminosity of the Sun
What different resistances can be obtained by using two 2. ? resistors and one 4. ? resistor?
What will be an ideal response?