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Common star 17 EP

HD 100340

RA 173.2081° · Dec 5.2767° · star

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Score breakdown

· 4 badges
17 pts · Common
Common 22 pts → Uncommon
  • Hot blue B-type star +6
  • Blue-white star +5
  • Star +3
  • On the zodiac +3
Total score 17

5 more points to reach Uncommon.

Badges

  • Star · +3
  • On the zodiac · +3
  • Hot blue B-type star · +6
  • Blue-white star · +5

Trivia

Hard to believe

  • True brightness. It pours out about 765.6 thousand 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 B9 — 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.

Find it in the sky

  • How to spot it. At magnitude 10.1 you'll want a small backyard telescope, over in Leo.
  • Seen from everywhere. It sits almost on the celestial equator, so it can be seen from essentially anywhere on Earth.
  • Best time of year. It stands highest in the middle of the night around March — 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 -0.2) — 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.

By the numbers

  • Surface temperature. Its colour puts the surface at roughly 14600 K, against the Sun's 5778 K.

Properties

absmag
-9.88
bv
-0.239
constellation
Leo
luminosity
779830.1105
mag
10.12
name
HD 100340
spect
B9

Nearby objects

About HD 100340

HD 100340 is a common star. It sits in the constellation Leo, shines at apparent magnitude 10.12 and has spectral type B9.

Its spectrum reads B9 — 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 100340 in the constellation Leo. At apparent magnitude 10.12, a small backyard telescope will bring it into view.

Like any astronomical target, HD 100340 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 100340 is a common star

HD 100340 scores 17 points on Spacedle's rarity scale, which places it in the common tier. Another 5 points would lift it into a rarer tier.

That score comes from 4 science badges — Star, On the zodiac, Hot blue B-type star 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.