An astronomer wants to observe a cloud of cold neutral (not ionized) hydrogen, far away from any stars. What would be an instrument that could help in this task?

Question

Quizplus · Accepted Answer

A radio telescope tuned to a wavelength of about 21 centimeters would be most useful for observing a cloud of cold neutral hydrogen, as this is the wavelength at which the hydrogen emits radiation. This type of observation is commonly used in astronomy and is known as 21-centimeter line spectroscopy. Option A is not appropriate, as x-rays are not emitted by cold neutral hydrogen. Option C would not be as effective as a radio telescope for this specific task, as visible light does not provide direct information about the existence of cold neutral hydrogen clouds. Option D is not appropriate because neutrinos are not emitted by cold neutral hydrogen. Option E is incorrect, as it is possible to observe clouds of hydrogen that are not near a star.

An Astronomer Wants to Observe a Cloud of Cold Neutral