science

Did you know that plants can also tell the time via a special protein (photoreceptor) that responds to a wavelength of light only occurring at dusk — far red light is light that has a longer wavelength than regular red light, but shorter than infrared.

Far red light occurs at dusk because as the Earth rotates, it effectively stretches out the light waves (from the perspective of a place where the sun is setting). It's basically the same phenomenon as how galaxies that are moving away from us appear to be red (red shift), but on a smaller more subtle scale.

Being able to detect far red light means that a plant can also use mechanisms involving this photoreceptor to perceive the changing of the seasons. For example, if on one day, the sun sets at 6:00pm, and the next day, it sets at 6:05pm, then 6:10pm etc., then the amount of time between each dusk is getting shorter, which means that it's spring. This is so cool and it blows my mind.