Remi Pearce, of Ilam School, asks :-
Why is black sand hotter than white sand?
Marlyn Jakub, a physicist at the University of Otago, responded.
For objects like sand, the colour is determined by the visible light reflected from the object's surfaces into your eyes.
Sunlight contains all colours. If the colour of the reflected light differs from white this tells us that some of the light energy was absorbed by the object. For dull, black objects like black sand, almost all incoming light energy from the source is absorbed, causing a rise in the temperature of the object. So in sunlight, the black sand temperature rises faster than that of the normal sand because the latter has pale-brown, semi-clear crystals which reflect much of the incoming light energy. Similarly, the surface of a black-painted car will also be hotter to the touch than the surface of a white-painted car, when both cars are in sunlight.
The dull black sand is not only a good absorber of the radiant energy of the Sun, it is also a good emitter of radiant energy, though these emitted waves are infrared waves and are unable to be seen by your eyes. If you were in a darkened room with a hot object, your skin would know when you got near to the hot object--no need to touch it!
Perhaps you can now consider a similar problem. On a cold winter night with clear skies and no wind, which car surface will cool down first and will have dew or frost forming on the roof first...the black-painted car or the white-painted car?