Rare variable star 41 EP

HD 172256

RA 280.0459° · Dec -22.6638° · star

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Score breakdown

· 7 badges

41 pts · Rare

Rare 50 pts → Epic

Bright giant +12
Toward the galactic centre +8
Hot blue B-type star +6
Variable star +5
Gently variable +4
On the zodiac +3
A named variable star +3

Total score 41

9 more points to reach Epic.

Badges

Variable star · +5
Toward the galactic centre · +8
On the zodiac · +3
Hot blue B-type star · +6
Bright giant · +12
Gently variable · +4
A named variable star · +3

Trivia

Hard to believe

True brightness. It pours out about 2.8 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(n) — 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.
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 8.7 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 brilliant white (B−V 0) — hotter and whiter than the Sun, the colour of Sirius or Vega.

Properties

absmag: -11.3
bv: 0.002
constellation: Sgr
luminosity: 2884031.5031
mag: 8.7
name: HD 172256
spect: B5II(n)
var amplitude: 0.1
var designation: V4131
var max: 8.641
var min: 8.741

Nearby objects

About HD 172256

HD 172256 is a rare variable star. It sits in the constellation Sgr, shines at apparent magnitude 8.7 and has spectral type B5II(n).

Its spectrum reads B5II(n) — 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 172256 in the constellation Sgr. At apparent magnitude 8.7, it is an easy target for binoculars.

Like any astronomical target, HD 172256 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 172256 is a rare variable star

HD 172256 scores 41 points on Spacedle's rarity scale, which places it in the rare tier. Another 9 points would lift it into a rarer tier.

That score comes from 7 science badges — Variable star, Toward the galactic centre, On the zodiac, Hot blue B-type star, Bright giant, Gently 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.