Question

A spaceship in our solar system emits a red light that is visible from Earth. As the spaceship moves away from Earth, light is no longer visible from the spaceship. Which of the following could explain this? The light can't reach Earth because the spaceship is moving away from Earth so quickly.
B. The light can't reach Earth because the spaceship has passed behind a nearby star.
C. The light has been shifted into the longer-wavelength, infrared section of the light spectrum, which is not visible.
D. The light has been shifted into the shorter-wavelength, ultraviolet section of the light spectrum, which is not visible.

Answer 1

Here are the possibilities I can think of:

-- The spaceship's headlights are pointed the other way, away from Earth.

-- The spaceship is behind a planet, a moon, an asteroid, or even behind
the sun, which is blocking it from our view.

-- The spaceship is moving AWAY from Earth so fast that its light is
red-shifted, to a longer wavelength which, for some odd reason, we
can't detect.  (Choice-C)
(This would require a barn-blasting speed, one that we have no way
to generate yet.)