What is Delta Cep primarily known as?

Delta Cep is primarily known as a Cepheid variable star. Cepheid variables are a specific type of star that pulsates in brightness at regular intervals, which allows astronomers to measure their periods of pulsation and relate this to their intrinsic brightness. This relationship is fundamental in establishing the distance scale of the universe, as it enables astronomers to calculate the distance to faraway galaxies by observing the brightness variations of Cepheid stars like Delta Cep.

Delta Cep itself has a well-defined period of about 5.366 days, during which it expands and contracts, causing its brightness to vary significantly. This characteristic has made it a vital tool in the field of distance measurement in astronomy, often referred to as the "standard candle" for determining distances across cosmic scales.