Suppose an astrophotographer hands you a picture with star trails taken looking toward the north celestial pole. If the star trails are 1/6 of a complete circle, about how many hours was the picture exposed? Hint: How many hours would it take the stars to make a full circle? Report your answer to the nearest whole number

Ultraviolet radiation is dangerous because it has a high enough energy to damage skin cells. what is the best explanation of the relationship between wavelength and wave energy? a) wave energy is related only to frequency, not wavelength. b) longer wavelengths have lower frequencies but higher energy. c) the shorter the wavelength, the lower the frequency and the higher the energy. d) the shorter the wavelength, the higher the frequency and the higher the energy.