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Rare star 43 EP

Kap Cru

RA 193.4538° · Dec -60.3762° · star

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Score breakdown

· 5 badges
43 pts · Rare
Rare 50 pts → Epic
  • Supergiant +18
  • Naked-eye visible +8
  • Under the Southern Cross +8
  • Hot blue B-type star +6
  • Star +3
Total score 43

7 more points to reach Epic.

Badges

  • Star · +3
  • Naked-eye visible · +8
  • Under the Southern Cross · +8
  • Hot blue B-type star · +6
  • Supergiant · +18

Trivia

What it actually is

  • Spectral class. Its spectrum reads B5Ia — 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 5.9 you can see it with your own eyes from a dark site, over in Crux.
  • Southern sky only. So far south it never rises for most of the northern hemisphere. To see it you'd have to travel to Chile, South Africa or Australia.
  • Best time of year. It stands highest in the middle of the night around April — that's when to go looking.

Its true colour

  • Its true colour. Measured through blue and visual filters it comes out brilliant white (B−V 0.2) — hotter and whiter than the Sun, the colour of Sirius or Vega.
  • 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 8160 K, against the Sun's 5778 K.

Properties

absmag
-14.11
bv
0.2
constellation
Cru
luminosity
38370724.5492
mag
5.89
name
Kap Cru
spect
B5Ia

About Kap Cru

Kap Cru is a rare star. It sits in the constellation Cru, shines at apparent magnitude 5.89 and has spectral type B5Ia.

Its spectrum reads B5Ia — 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 Kap Cru in the constellation Cru. At apparent magnitude 5.89, it can be glimpsed with the unaided eye under dark skies.

Like any astronomical target, Kap Cru 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 Kap Cru is a rare star

Kap Cru scores 43 points on Spacedle's rarity scale, which places it in the rare tier. Another 7 points would lift it into a rarer tier.

That score comes from 5 science badges — Star, Naked-eye visible, Under the Southern Cross, 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.