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Common variable star 21 EP

HD 209869

RA 331.1160° · Dec 62.4076° · star

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Score breakdown

· 5 badges
21 pts · Common
Common 22 pts → Uncommon
  • Variable star +5
  • White A-type star +5
  • Never sets (northern circumpolar) +4
  • Gently variable +4
  • A named variable star +3
Total score 21

1 more point to reach Uncommon.

Badges

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

Trivia

Hard to believe

  • True brightness. It pours out about 3.6 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 A0 — an A-type star: white-hot, typically about twice the Sun's mass, and the class most of the sky's famous bright stars belong to.
  • 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 8.4 it is just past naked-eye reach — ordinary binoculars will pull it in, over in Cepheus.
  • 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 August — 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
-11.56
bv
0.15
constellation
Cep
luminosity
3664375.7465
mag
8.44
name
HD 209869
spect
A0
var amplitude
0.19
var designation
V443
var max
8.41
var min
8.6

Nearby objects

About HD 209869

HD 209869 is a common variable star. It sits in the constellation Cep, shines at apparent magnitude 8.44 and has spectral type A0.

Its spectrum reads A0 — an A-type star: white-hot, typically about twice the Sun's mass, and the class most of the sky's famous bright stars belong to.

How to see it

Look for HD 209869 in the constellation Cep. At apparent magnitude 8.44, it is an easy target for binoculars.

Like any astronomical target, HD 209869 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 209869 is a common variable star

HD 209869 scores 21 points on Spacedle's rarity scale, which places it in the common tier. Another 1 point would lift it into a rarer tier.

That score comes from 5 science badges — Variable star, Never sets (northern circumpolar), White A-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.