What kind of light can be detected from an airplane but not from the ground?
A) most infrared light
B) only the shortest-wavelength infrared light
C) radio waves
D) x-rays
A) most infrared light
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The dark age started as the first stars began to form
Indicate whether the statement is true or false
Mercury is visible to us:
A. only in the summer. B. only in the winter. C. only very briefly near sunrise or sunset. D. only during its new phase. E. only during the several hours around midnight
Which of the following best describes the development of astronomical telescopes over the past 60 years?
A) Over the 60-year period, telescopes have gradually gotten bigger and more powerful. B) Although there have been advances in cameras and computing power, telescopes themselves have not changed much in the last 60 years. C) The world's most powerful telescope remained the same for most of this period, but in the past 20 years many new and more powerful telescopes have been built. D) The only major change in telescope power has occurred because of our ability to launch telescopes into space rather than operating them only from the ground.
The figure shows two point sources of light, A and B, that emit light waves in phase with each other. A is a distance of 3? from point P. B is distant 5? from P. (? is the wavelength.) The phase difference between the waves arriving at P from A and B is
?
?
a.
0 rad.
b.
? rad.
c.
2? rad.
d.
3? rad.
e.
4? rad.