I have a simple question about a relativistic Doppler effect problem. To keep the math simple, I have intentionally left out the labels, you can view the speed of light as 300 miles per seconds, or 300 meters per second, it isn’t important. Speed of light = 300 per second Wavelength of light = 4 Frequency of light = 75 cycles per second Formula: Wavelength (4) * Frequency (75) = Speed (300) If an observer travels towards the source at a constant speed of 2 per second, he would expect the relative speed to be 302 per second. The observer’s speed has caused the frequency to increase. He now measures the frequency to be 75.5 cycles per second. If he divides the speed (302) by the new frequency (75.5) he calculates the wavelength to be 4. Knowing the speed of light has to remain constant, he divides the speed of light by the measured frequency and now calculates the wavelength to be 3.973509934 Is this right? When I use the following formula… (C-Vs)T / Sq.Root of (1-(Vs Squared /C Squared)) C = 300 Vs = 2 T = 1/75 …I calculate the wavelength to be 3.973421633 Why do I calculate 2 different answers, what have I done wrong? It seems to me that 3.973509934 has to be correct in order to multiply it by the frequency and get the speed of light.