Which phenomenon occurs when light from an object is shifted towards longer wavelengths?

The phenomenon that occurs when light from an object is shifted towards longer wavelengths is known as redshift. This effect happens when an object emitting light is moving away from the observer, causing the wavelengths of the emitted light to stretch. As a result, the light shifts towards the red end of the spectrum, where wavelengths are longer compared to blue light, which has shorter wavelengths.

Redshift is a crucial concept in astronomy as it provides evidence of the expansion of the universe. When observing distant galaxies, astronomers note that the light we receive is redshifted, indicating that those galaxies are moving away from us. This relationship is described by Hubble's Law, which correlates the redshift of light from galaxies with their distance from Earth.

Other options mentioned do not relate to the phenomenon of shifting light towards longer wavelengths. For example, blue shift refers to the opposite effect, where light is shifted towards shorter wavelengths as objects move closer to the observer. A light year is a measure of distance, specifically the distance light travels in one year. Stellar parallax is the apparent shift in position of a nearby star against a distant background star, which helps in measuring distances to stars but does not involve any shifting of wavelengths.