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Common variable star 18 EP

HD 173539

RA 281.8846° · Dec -38.1590° · star

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Score breakdown

· 3 badges
18 pts · Common
Common 22 pts → Uncommon
  • Strongly variable +10
  • Variable star +5
  • A named variable star +3
Total score 18

4 more points to reach Uncommon.

Badges

  • Variable star · +5
  • Strongly variable · +10
  • A named variable star · +3

Trivia

Hard to believe

  • True brightness. It pours out about 855.1 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 R0 — a carbon star, wrapped in so much soot that its light is filtered to a deep ruby red.
  • It changes. This star does not hold still: its brightness rises and falls on a rhythm of hours, days or years, either pulsing in size or being eclipsed by a companion.

Find it in the sky

  • How to spot it. At magnitude 10 you'll want a small backyard telescope, over in Corona Australis.
  • 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 yellow (B−V 0.6) — almost exactly the Sun's own shade — a stellar twin in colour, if not in size.
  • 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
-10
bv
0.628
constellation
CrA
luminosity
870963.59
mag
10
name
HD 173539
spect
R0
var amplitude
0.9
var designation
V
var max
9.871
var min
10.771

Nearby objects

About HD 173539

HD 173539 is a common variable star. It sits in the constellation CrA, shines at apparent magnitude 10 and has spectral type R0.

Its spectrum reads R0 — a carbon star, wrapped in so much soot that its light is filtered to a deep ruby red.

How to see it

Look for HD 173539 in the constellation CrA. At apparent magnitude 10, a small backyard telescope will bring it into view.

Like any astronomical target, HD 173539 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 173539 is a common variable star

HD 173539 scores 18 points on Spacedle's rarity scale, which places it in the common tier. Another 4 points would lift it into a rarer tier.

That score comes from 3 science badges — Variable star, Strongly variable and A named variable 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.