Why Is It That We Will Not See Fluctuations in Light

question 74

Multiple Choice

Why is it that we will not see fluctuations in light output in times shorter than about 1 day when we observe an extragalactic source whose diameter is about 1 light-day?

• A) Absorption of light by intergalactic matter will smooth out rapid fluctuations within the beam.
• B) The light from different parts of the source will be Doppler-shifted by different amounts, allowing us to see only an average shift.
• C) It is inconceivable that a source of this size could vary on such short time scales.
• D) Arrival times will be different from different parts of the source, which will smooth out short-term fluctuations.

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Definitions:

Voice Box

The part of the air passage to the lungs that holds the vocal cords; it is responsible for producing sound.

Larynx

The voice box located in the throat, involved in breathing, producing sound, and protecting the trachea against food aspiration.

Trachea

The windpipe, a tube that connects the larynx to the bronchi of the lungs.

Pharynx

A muscular tube that connects the mouth and nasal passages with the esophagus and larynx, serving both respiratory and digestive functions.