What Use Are 21 Cm Radio Waves to Galactic Astronomers

question 85

Multiple Choice

What use are 21 cm radio waves to galactic astronomers?

• A)They cut through the dusty cocoons to let us watch star birth.
• B)We can reflect them off the core of the Galaxy.
• C)Their Doppler shifts let us map the motions and locations of gas in the spiral arms.
• D)They bounce off stars like our Sun to let us precisely measure their distances.
• E)They pick up the cool, dark matter much better than can optical telescopes.

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