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Uncommon star 31 EP

HD 236740

RA 21.8597° · Dec 60.2845° · star

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Score breakdown

· 4 badges
31 pts · Uncommon
Uncommon 34 pts → Rare
  • Supergiant +18
  • Hot blue B-type star +6
  • Never sets (northern circumpolar) +4
  • Star +3
Total score 31

3 more points to reach Rare.

Badges

  • Star · +3
  • Never sets (northern circumpolar) · +4
  • Hot blue B-type star · +6
  • Supergiant · +18

Trivia

What it actually is

  • Spectral class. Its spectrum reads B3Ia — 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.
  • Where it is in life. It is a luminous supergiant — among the largest and rarest stars in the galaxy.

Find it in the sky

  • How to spot it. At magnitude 7.9 it is just past naked-eye reach — ordinary binoculars will pull it in, over in Cassiopeia.
  • Never sets. So far north that from Britain, Canada or northern Europe it never dips below the horizon — it is up every clear night of the year.
  • Best time of year. It stands highest in the middle of the night around October — that's when to go looking.

Its true colour

  • Its true colour. Measured through blue and visual filters it comes out yellow-white (B−V 0.5) — a shade brighter and crisper than our own Sun.
  • Why no green stars. No star ever looks green: a surface hot enough to peak in green also floods out plenty of red and blue, and your eye blends the mixture back to white.

By the numbers

  • Surface temperature. Its colour puts the surface at roughly 6590 K, against the Sun's 5778 K.

Properties

absmag
-12.11
bv
0.457
constellation
Cas
luminosity
6081350.0128
mag
7.89
name
HD 236740
spect
B3Ia

About HD 236740

HD 236740 is an uncommon star. It sits in the constellation Cas, shines at apparent magnitude 7.89 and has spectral type B3Ia.

Its spectrum reads B3Ia — 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.

How to see it

Look for HD 236740 in the constellation Cas. At apparent magnitude 7.89, it is an easy target for binoculars.

Like any astronomical target, HD 236740 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.

Why HD 236740 is an uncommon star

HD 236740 scores 31 points on Spacedle's rarity scale, which places it in the uncommon tier. Another 3 points would lift it into a rarer tier.

That score comes from 4 science badges — Star, Never sets (northern circumpolar), Hot blue B-type star and Supergiant — 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.