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Rare variable star 42 EP

HD 215835

RA 341.7255° · Dec 58.0843° · star

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Score breakdown

· 5 badges
42 pts · Rare
Rare 50 pts → Epic
  • Blazing O-type star +26
  • Variable star +5
  • Never sets (northern circumpolar) +4
  • Gently variable +4
  • A named variable star +3
Total score 42

8 more points to reach Epic.

Badges

  • Variable star · +5
  • Never sets (northern circumpolar) · +4
  • Blazing O-type star · +26
  • Gently variable · +4
  • A named variable star · +3

Trivia

Hard to believe

  • True brightness. It pours out about 3.1 million times as much light as the Sun. It only looks ordinary because it is so far away.

What it actually is

  • Spectral class. Its spectrum reads O5.5 — an O-type star — the hottest, rarest main class there is. Fewer than one star in a million is an O, and none of them lasts long.
  • 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 8.6 it is just past naked-eye reach — ordinary binoculars will pull it in, over in Cepheus.
  • Northern sky. It rides the northern half of the sky — an easier target the further north you are.
  • 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 yellow-white (B−V 0.3) — 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.

Properties

absmag
-11.41
bv
0.334
constellation
Cep
luminosity
3191537.8551
mag
8.59
name
HD 215835
spect
O5.5
var amplitude
0.08
var designation
DH
var max
8.552
var min
8.632

About HD 215835

HD 215835 is a rare variable star. It sits in the constellation Cep, shines at apparent magnitude 8.59 and has spectral type O5.5.

Its spectrum reads O5.5 — an O-type star — the hottest, rarest main class there is. Fewer than one star in a million is an O, and none of them lasts long.

How to see it

Look for HD 215835 in the constellation Cep. At apparent magnitude 8.59, it is an easy target for binoculars.

Like any astronomical target, HD 215835 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 215835 is a rare variable star

HD 215835 scores 42 points on Spacedle's rarity scale, which places it in the rare tier. Another 8 points would lift it into a rarer tier.

That score comes from 5 science badges — Variable star, Never sets (northern circumpolar), Blazing O-type star, 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.