electromagnetic waves  transfer of energy by a disturbance
		� Young�s experiment  wave nature �  = wavelength = length between crests/valleys �  = frequency = number of crests passing per unit time � ���������������������� = cycles per sec (Hz) = 1/P � P = period = time for wave to repeat itself � = c (speed of light - celeritas) = 3 x 1010 cm/sec ����� = 300, 000 km/s visible light:� 4000    8000 �ngstrom (1� = 10-8 cm) For a star, let B= brightness = power/area = power/4d2 If L = total output of star, L = Bx4d2� and B = L/4d2