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Rare star 37 EP

HD 172431

RA 280.3268° · Dec -28.8257° · star

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Score breakdown

· 6 badges
37 pts · Rare
Rare 50 pts → Epic
  • Bright giant +12
  • Toward the galactic centre +8
  • Hot blue B-type star +6
  • Blue-white star +5
  • Star +3
  • On the zodiac +3
Total score 37

13 more points to reach Epic.

Badges

  • Star · +3
  • Toward the galactic centre · +8
  • On the zodiac · +3
  • Hot blue B-type star · +6
  • Bright giant · +12
  • Blue-white star · +5

Trivia

Hard to believe

  • True brightness. It pours out about 4 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 B5II/III — 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 bright giant, well on its way to the largest stars there are.

Find it in the sky

  • How to spot it. At magnitude 8.3 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 July — that's when to go looking.

Its true colour

  • Its true colour. Measured through blue and visual filters it comes out blue-white (B−V -0) — the hallmark of a surface far hotter than the Sun's.
  • 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
-11.68
bv
-0.027
constellation
Sgr
luminosity
4092606.5973
mag
8.32
name
HD 172431
spect
B5II/III

About HD 172431

HD 172431 is a rare star. It sits in the constellation Sgr, shines at apparent magnitude 8.32 and has spectral type B5II/III.

Its spectrum reads B5II/III — 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 172431 in the constellation Sgr. At apparent magnitude 8.32, it is an easy target for binoculars.

Like any astronomical target, HD 172431 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 172431 is a rare star

HD 172431 scores 37 points on Spacedle's rarity scale, which places it in the rare tier. Another 13 points would lift it into a rarer tier.

That score comes from 6 science badges — Star, Toward the galactic centre, On the zodiac, Hot blue B-type star, Bright giant and Blue-white 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.