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Rare star 38 EP

HD 166689

RA 273.1149° · Dec -16.3807° · star

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Score breakdown

· 5 badges
38 pts · Rare
Rare 50 pts → Epic
  • Supergiant +18
  • Toward the galactic centre +8
  • Hot blue B-type star +6
  • Star +3
  • On the zodiac +3
Total score 38

12 more points to reach Epic.

Badges

  • Star · +3
  • Toward the galactic centre · +8
  • On the zodiac · +3
  • Hot blue B-type star · +6
  • Supergiant · +18

Trivia

What it actually is

  • Spectral class. Its spectrum reads B1Ib — 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 7.5 it is just past naked-eye reach — ordinary binoculars will pull it in, over in Sagittarius.
  • Southern sky. It rides the southern half of the sky — an easier target the further south you are.
  • Best time of year. It stands highest in the middle of the night around June — 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.

By the numbers

  • Surface temperature. Its colour puts the surface at roughly 8660 K, against the Sun's 5778 K.

Properties

absmag
-12.49
bv
0.14
constellation
Sgr
luminosity
8629785.4777
mag
7.51
name
HD 166689
spect
B1Ib

About HD 166689

HD 166689 is a rare star. It sits in the constellation Sgr, shines at apparent magnitude 7.51 and has spectral type B1Ib.

Its spectrum reads B1Ib — 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 166689 in the constellation Sgr. At apparent magnitude 7.51, it is an easy target for binoculars.

Like any astronomical target, HD 166689 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 166689 is a rare star

HD 166689 scores 38 points on Spacedle's rarity scale, which places it in the rare tier. Another 12 points would lift it into a rarer tier.

That score comes from 5 science badges — Star, Toward the galactic centre, On the zodiac, 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.