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Uncommon variable star 27 EP

HD 7681

RA 19.5299° · Dec 61.7179° · star

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Score breakdown

· 6 badges
27 pts · Uncommon
Uncommon 34 pts → Rare
  • Deep red star +8
  • Variable star +5
  • Never sets (northern circumpolar) +4
  • Gently variable +4
  • Orange K-type star +3
  • A named variable star +3
Total score 27

7 more points to reach Rare.

Badges

  • Variable star · +5
  • Never sets (northern circumpolar) · +4
  • Orange K-type star · +3
  • Deep red star · +8
  • Gently variable · +4
  • A named variable star · +3

Trivia

What it actually is

  • Spectral class. Its spectrum reads K5 — a K-type star. Orange K dwarfs are the marathon runners of the galaxy, burning steadily for tens of billions of years.
  • 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 7.7 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 deep orange-red (B−V 1.8) — one of the coolest surfaces a star can have while still fusing.

By the numbers

  • Surface temperature. Its colour puts the surface at roughly 3450 K, against the Sun's 5778 K.

What's in a name

  • Its catalogue. The HD number is from the Henry Draper Catalogue, in which Annie Jump Cannon personally classified the spectra of nearly 400,000 stars — still the largest such feat by one person.

Properties

absmag
-12.33
bv
1.756
constellation
Cas
luminosity
7447319.7391
mag
7.67
name
HD 7681
spect
K5
var amplitude
0.06
var designation
V538
var max
7.639
var min
7.699

About HD 7681

HD 7681 is an uncommon variable star. It sits in the constellation Cas, shines at apparent magnitude 7.67 and has spectral type K5.

Its spectrum reads K5 — a K-type star. Orange K dwarfs are the marathon runners of the galaxy, burning steadily for tens of billions of years.

How to see it

Look for HD 7681 in the constellation Cas. At apparent magnitude 7.67, it is an easy target for binoculars.

Like any astronomical target, HD 7681 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 7681 is an uncommon variable star

HD 7681 scores 27 points on Spacedle's rarity scale, which places it in the uncommon tier. Another 7 points would lift it into a rarer tier.

That score comes from 6 science badges — Variable star, Never sets (northern circumpolar), Orange K-type star, Deep red 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.