Why do predator repeatedly avoid prey that is red in color?

If a clock aboard a space ship traveling at 0.900 c of the speed of light relative to earth chimes once at the beginning of the hour and again when it reads one hour later, how much time would an observer on earth say elapsed between the two chimes?

Ascientist is tracking an object orbiting the sun that is found between mars and jupiter. in order to classify the object as an asteroid, it must be at least

What is special about a dc circuit ?