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Uncommon star 30 EP

HD 842

RA 3.2515° · Dec 55.8590° · star

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Score breakdown

· 4 badges
30 pts · Uncommon
Uncommon 34 pts → Rare
  • Supergiant +18
  • White A-type star +5
  • Never sets (northern circumpolar) +4
  • Star +3
Total score 30

4 more points to reach Rare.

Badges

  • Star · +3
  • Never sets (northern circumpolar) · +4
  • White A-type star · +5
  • Supergiant · +18

Trivia

What it actually is

  • Spectral class. Its spectrum reads A9Iab: — an A-type star: white-hot, typically about twice the Sun's mass, and the class most of the sky's famous bright stars belong to.
  • Where it is in life. It is a supergiant. Drop it where the Sun is and its surface would engulf the inner planets.

Find it in the sky

  • How to spot it. At magnitude 7.9 it is just past naked-eye reach — ordinary binoculars will pull it in, over in Cassiopeia.
  • 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 September — that's when to go looking.

Its true colour

  • Its true colour. Measured through blue and visual filters it comes out yellow-white (B−V 0.5) — a shade brighter and crisper than our own Sun.
  • 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 6380 K, against the Sun's 5778 K.

Properties

absmag
-12.06
bv
0.501
constellation
Cas
luminosity
5807644.1752
mag
7.94
name
HD 842
spect
A9Iab:

About HD 842

HD 842 is an uncommon star. It sits in the constellation Cas, shines at apparent magnitude 7.94 and has spectral type A9Iab:.

Its spectrum reads A9Iab: — an A-type star: white-hot, typically about twice the Sun's mass, and the class most of the sky's famous bright stars belong to.

How to see it

Look for HD 842 in the constellation Cas. At apparent magnitude 7.94, it is an easy target for binoculars.

Like any astronomical target, HD 842 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 842 is an uncommon star

HD 842 scores 30 points on Spacedle's rarity scale, which places it in the uncommon tier. Another 4 points would lift it into a rarer tier.

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