Where does the 21-cm radiation arise?
What will be an ideal response?
When the electron orbiting the proton in hydrogen flips its spin, the energy radiated has a wavelength of 21 cm, and is detected with radio telescopes.
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What is the approximate latitude of the observer in the diagram below?
a.
20° N
b.
20° S
c.
70° N
d.
70° S
e.
0°
When equilibrium was established in Procedure 1, Part 1, what was the relationship between the two forces and the length of their lever arms?
The figure above shows the geological time scale of Earth. The time since dinosaurs went extinct (with the K-T event) represents approximately ________ of the Earth's history.
A) 0.15% B) 1.5% C) 15% D) 50%
The masses of most spiral galaxies, like ours, are a few billion solar masses
Indicate whether the statement is true or false