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Uncommon star 31 EP

HD 17857

RA 43.8373° · Dec 64.1574° · star

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Score breakdown

· 4 badges
31 pts · Uncommon
Uncommon 34 pts → Rare
  • Supergiant +18
  • Hot blue B-type star +6
  • Never sets (northern circumpolar) +4
  • Star +3
Total score 31

3 more points to reach Rare.

Badges

  • Star · +3
  • Never sets (northern circumpolar) · +4
  • Hot blue B-type star · +6
  • Supergiant · +18

Trivia

What it actually is

  • Spectral class. Its spectrum reads B8Ib — 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 supergiant, hundreds of times wider than the Sun.

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 November — that's when to go looking.

Its true colour

  • Its true colour. Measured through blue and visual filters it comes out yellow (B−V 0.7) — almost exactly the Sun's own shade — a stellar twin in colour, if not in size.
  • 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 5470 K, against the Sun's 5778 K.

Properties

absmag
-12.3
bv
0.741
constellation
Cas
luminosity
7244359.6007
mag
7.7
name
HD 17857
spect
B8Ib

About HD 17857

HD 17857 is an uncommon star. It sits in the constellation Cas, shines at apparent magnitude 7.7 and has spectral type B8Ib.

Its spectrum reads B8Ib — 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 HD 17857 in the constellation Cas. At apparent magnitude 7.7, it is an easy target for binoculars.

Like any astronomical target, HD 17857 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 17857 is an uncommon star

HD 17857 scores 31 points on Spacedle's rarity scale, which places it in the uncommon tier. Another 3 points would lift it into a rarer tier.

That score comes from 4 science badges — Star, Never sets (northern circumpolar), 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.