A double star distinguishable by a small telescope with a 6 cm diameter objective, consisting of two components with magnitudes 3.2 (bright white) and 7.9 (blue - appearing emerald green in a large telescope) at a mutual distance of 13.3". The primary star is also a spectroscopic binary, with an orbital period of only 4 and 3/4 hours. In the same period, it exhibits a slight change in brightness between magnitudes 3.3 and 3.4. It is even a prototype of a group of variable stars called beta Cepheids, whose brightness fluctuations are so small that they can hardly be observed with the naked eye. It is located at a distance of 690 light-years.