# Determining the Speed of Recession of the Galaxy Hydra

The light emitted by a galaxy contains a continuous distribution of wavelengths because the galaxy is composed of millions of stars and other thermal emitters. However, some narrow gaps occur in the continuous spectrum where the radiation has been strongly absorbed by cooler gases in the galaxy. In particular, a cloud of ionized calcium atoms produces very strong absorption at $$394 \text{ nm}$$ for a galaxy at rest with respect to the Earth. For the galaxy Hydra, which is 200 million ly away, this absorption is shifted to $$475 \text{ nm}$$. How fast is Hydra moving away from the Earth?

• Speed of light is $$299792458 \text{ m/s}$$.
• Give your answer in $$m/s$$ unit.