Suppose an Observer Were Far from a Planet That Had $\alpha$

question 21

Multiple Choice

Suppose an observer were far from a planet that had a very strong gravitational field, and a light wave reaches the observer from a source of hydrogen (H _$\alpha$ ) light on the surface of the planet. For an H _$\alpha$ light source in the observer's own spaceship, the wavelength is 656.3 nm. What wavelength does the observer see when looking at the light source on the planet?

• A) shorter than 656.3 nm
• B) longer than 656.3 nm
• C) infinite, since the source is in a gravitational field
• D) 656.3 nm, the same as from the spaceship's light source

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