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Rare variable star 48 EP

15Kap Cas

RA 8.2500° · Dec 62.9318° · star

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Score breakdown

· 7 badges
48 pts · Rare
Rare 50 pts → Epic
  • Supergiant +18
  • Naked-eye visible +8
  • Hot blue B-type star +6
  • Variable star +5
  • Never sets (northern circumpolar) +4
  • Gently variable +4
  • A named variable star +3
Total score 48

2 more points to reach Epic.

Badges

  • Variable star · +5
  • Naked-eye visible · +8
  • Never sets (northern circumpolar) · +4
  • Hot blue B-type star · +6
  • Supergiant · +18
  • Gently variable · +4
  • A named variable star · +3

Trivia

What it actually is

  • Spectral class. Its spectrum reads B1Ia — 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.
  • It changes. This star does not hold still: its brightness rises and falls on a rhythm of hours, days or years, either pulsing in size or being eclipsed by a companion.

Find it in the sky

  • How to spot it. At magnitude 4.2 you can see it with your own eyes from a dark site, 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 September — 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 0.1) — 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.

Properties

absmag
-15.83
bv
0.13
constellation
Cas
luminosity
187068214.0366
mag
4.17
name
15Kap Cas
spect
B1Ia
var amplitude
0.07
var designation
Kap
var max
4.14
var min
4.21

About 15Kap Cas

15Kap Cas is a rare variable star. It sits in the constellation Cas, shines at apparent magnitude 4.17 and has spectral type B1Ia.

Its spectrum reads B1Ia — 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 15Kap Cas in the constellation Cas. At apparent magnitude 4.17, it can be glimpsed with the unaided eye under dark skies.

Like any astronomical target, 15Kap Cas 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 15Kap Cas is a rare variable star

15Kap Cas scores 48 points on Spacedle's rarity scale, which places it in the rare tier. Another 2 points would lift it into a rarer tier.

That score comes from 7 science badges — Variable star, Naked-eye visible, Never sets (northern circumpolar), Hot blue B-type star, Supergiant, Gently variable 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.