---
name: Alfirk (β Cep)
constellation: Cep
created_by: editor.cs
created_date: 2022-01-21 17:00:00
updated_by: skybber
updated_date: 2022-01-23 13:37:51.531863
---
a binary star resolvable in a small telescope with a 6 cm diameter objective lens, consisting of two components of 3.2mag (bright white) and 7.9mag (blue - emerald green in a large telescope) at a mutual distance of 13.3". The main star is also a spectroscopic binary, with an orbital period of only 4 and 3/4 hours. At the same period it shows a slight change in brightness between 3.3mag and 3.4mag. It is even the prototype of a group of variable stars called beta Cepheids, whose brightness variations are so small that they are barely perceptible to the eye. It lies at a distance of 690 light years.