RA 52.6124° · Dec 47.0633° · star
9 more points to reach Rare.
HD 21540 is an uncommon star. It lies about 2,434 light-years from Earth, sits in the constellation Per, shines at apparent magnitude 7.03 and has spectral type B8.
Its spectrum reads B8 — 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 HD 21540 in the constellation Per. At apparent magnitude 7.03, it is an easy target for binoculars.
Like any astronomical target, HD 21540 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.
HD 21540 scores 25 points on Spacedle's rarity scale, which places it in the uncommon tier. Another 9 points would lift it into a rarer tier.
That score comes from 4 science badges — Star, Distant (over 1,000 light-years), Hot blue B-type star and Intrinsically luminous (Mv < −2) — 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.