This lesson uses a simple discrepant event to demonstrate the underlying cause for early miscalculation of the size of the Milky Way galaxy. By standardizing the Cepheid period-luminosity relationship without recognizing there were two types of... (View More) Cepheid variable stars with intrinsic differences in absolute magnitude, a distance calculation error occurred. Requires two lamps and two soft-white light bulbs: 25 watt and 60 watt (estimated materials cost is for light bulbs). This lesson is part of the Cosmic Times teachers guide and is intended to be used in conjunction with the 1955 Cosmic Times Poster. (View Less)