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Uncommon star 27 EP

HD 42400

RA 92.8466° · Dec 20.9054° · star

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Score breakdown

· 4 badges
27 pts · Uncommon
Uncommon 34 pts → Rare
  • Bright giant +12
  • In Orion's hunting ground +6
  • Hot blue B-type star +6
  • Star +3
Total score 27

7 more points to reach Rare.

Badges

  • Star · +3
  • In Orion's hunting ground · +6
  • Hot blue B-type star · +6
  • Bright giant · +12

Trivia

What it actually is

  • Spectral class. Its spectrum reads B5II — 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 6.8 it is just past naked-eye reach — ordinary binoculars will pull it in, over in Orion.
  • Northern sky. It rides the northern half of the sky — an easier target the further north you are.
  • Best time of year. It stands highest in the middle of the night around December — 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 0.2) — 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 8530 K, against the Sun's 5778 K.

Properties

absmag
-13.16
bv
0.155
constellation
Ori
luminosity
15995580.2861
mag
6.84
name
HD 42400
spect
B5II

About HD 42400

HD 42400 is an uncommon star. It sits in the constellation Ori, shines at apparent magnitude 6.84 and has spectral type B5II.

Its spectrum reads B5II — 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 42400 in the constellation Ori. At apparent magnitude 6.84, it is an easy target for binoculars.

Like any astronomical target, HD 42400 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 42400 is an uncommon star

HD 42400 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 4 science badges — Star, In Orion's hunting ground, Hot blue B-type star and Bright giant — 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.