RA 44.3220° · Dec 31.9342° · star
5 more points to reach Rare.
21 Per is an uncommon variable star. It lies about 319.8 light-years from Earth, sits in the constellation Per, shines at apparent magnitude 5.1 and has spectral type B9p....
Its spectrum reads B9p... — a blue-white B-type star, with a surface tens of thousands of degrees hot and a life measured in tens of millions of years.
Look for 21 Per in the constellation Per. At apparent magnitude 5.1, it can be glimpsed with the unaided eye under dark skies.
Like any astronomical target, 21 Per is best seen from a dark site away from city lights, and when it is above the horizon depends on your latitude and the time of year. The visibility panel above works out tonight's viewing window for your saved location.
21 Per scores 29 points on Spacedle's rarity scale, which places it in the uncommon tier. Another 5 points would lift it into a rarer tier.
That score comes from 6 science badges — Variable star, Naked-eye visible, Hot blue B-type star, Blue-white star, Barely variable (under 0.05 mag) and A named variable star — each earned for a real, measurable property of the object. Rarity on Spacedle is never random: the more remarkable an object's astrophysics, the more badges it collects, the higher it scores, and the rarer it ranks.