According to the Doppler effect, what does it signify when stars appear redder than expected?

When stars appear redder than expected, it indicates that they are moving away from us, a phenomenon known as redshift. The Doppler effect explains how the wavelength of light from an object changes as that object moves relative to an observer. Specifically, when an object moves away, the waves stretch, which increases the wavelength of the light emitted. This shift towards the red end of the spectrum signifies that the star is receding from the observer.

In the context of the universe, redshift is an important observation, as it supports the idea of an expanding universe, where distant galaxies and stars are moving away from us. By measuring the amount of redshift, astronomers can determine the speed at which these celestial bodies are receding.

The other options do not reflect the correct interpretation of redshift. For instance, if a star were hotter than expected, it would actually emit light that appears bluer due to the associated shift in wavelengths. Similarly, a star moving towards us would exhibit blueshift, where its light waves compress, resulting in shorter wavelengths and a shift toward the blue end of the spectrum. Emitting less light does not relate to the Doppler effect but rather to other factors affecting a star's luminosity.