Blue stars are the hottest stars in the universe. While people often associate red with hot and blue with cold, as objects warm beyond the point of red hot, their color changes, eventually becoming blue. Other examples of blue things include blue crabs and the sky.
Blue crabs have blue pinchers, and humans value them highly for their succulent, sweet meat. They grow along the eastern coast of North and South America from Nova Scotia to Uruguay. Their shells are brown, and the female blue crab has red accents on its claws. Blue crabs eat practically anything that gets in the reach of their large pinchers, including fish, mussels, snails, carrion and smaller blue crabs. The shells of male blue crabs grow to 9 inches in width.
Humans perceive the sky as blue due to the scattering of sunlight. Light travels in waves, and the molecules of air in the atmosphere act as tiny prisms to disperse the light. Blue light has the shortest wavelength in the spectrum, and the air disperses it more than any other color, giving the sky a blue appearance when the sun is overhead. However, when the angle of the sun is near the horizon, the change in the viewing angle means light must pass through more of the atmosphere. The blue light disperses quickly, allowing more of the yellow and red colors to reach the observer's eyes, giving sunrises and sunsets a red appearance.