Uncommon star 31 EP

HD 172533

RA 280.4481° · Dec -27.4448° · star

Loading sky survey…

🌌 View in 3D star map

Tonight’s visibility

Computing the sky for your location…

Score breakdown

· 6 badges

31 pts · Uncommon

Uncommon 34 pts → Rare

Toward the galactic centre +8
Hot blue B-type star +6
Giant star +6
Blue-white star +5
Star +3
On the zodiac +3

Total score 31

3 more points to reach Rare.

Badges

Star · +3
Toward the galactic centre · +8
On the zodiac · +3
Hot blue B-type star · +6
Giant star · +6
Blue-white star · +5

Trivia

Hard to believe

True brightness. It pours out about 4.1 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 B2III/IV — 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 giant. It has already exhausted its core hydrogen and swollen up enormously in response.

Find it in the sky

How to spot it. At magnitude 8.3 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 blue-white (B−V -0) — 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.

Properties

absmag: -11.7
bv: -0.017
constellation: Sgr
luminosity: 4168693.8347
mag: 8.3
name: HD 172533
spect: B2III/IV

Nearby objects

About HD 172533

HD 172533 is an uncommon star. It sits in the constellation Sgr, shines at apparent magnitude 8.3 and has spectral type B2III/IV.

Its spectrum reads B2III/IV — 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 172533 in the constellation Sgr. At apparent magnitude 8.3, it is an easy target for binoculars.

Like any astronomical target, HD 172533 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 172533 is an uncommon star

HD 172533 scores 31 points on Spacedle's rarity scale, which places it in the uncommon tier. Another 3 points would lift it into a rarer tier.

That score comes from 6 science badges — Star, Toward the galactic centre, On the zodiac, Hot blue B-type star, Giant 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.