Together with the stars ε (4.19mag) and ζ Cep (3.35mag), it forms a small triangle. While these two stars are constant, δ Cephei changes its brightness regularly due to pulsation. The entire group of variable stars - delta Cepheids - is named after this star. The variability of δ Cephei was discovered in 1784 by the twenty-year-old John Goodrick, a deaf-mute English amateur astronomer of Dutch origin (he discovered three variable stars, thoroughly studied the brightness changes of the star Algol, and correctly explained them at the age of 19, two years later he died at the age of 21). In its brightest form, the star reaches a magnitude of 3.48, while in its minimum it has a brightness of 4.37mag, so these changes can be easily observed with the naked eye. Its period is 5.37 days. Astronomers use Cepheids to estimate distances in the universe.