Rare star 42 EP

HD 109978

RA 189.9069° · Dec -62.4336° · star

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Score breakdown

· 4 badges

42 pts · Rare

Rare 50 pts → Epic

Blazing O-type star +26
Under the Southern Cross +8
Subgiant (leaving the main sequence) +5
Star +3

Total score 42

8 more points to reach Epic.

Badges

Star · +3
Under the Southern Cross · +8
Blazing O-type star · +26
Subgiant (leaving the main sequence) · +5

Trivia

Hard to believe

True brightness. It pours out about 2.6 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 O9IV — an O-type star — the hottest, rarest main class there is. Fewer than one star in a million is an O, and none of them lasts long.
Where it is in life. It is a subgiant, caught in the act of leaving the main sequence as the hydrogen in its core runs out.

Find it in the sky

How to spot it. At magnitude 8.8 it is just past naked-eye reach — ordinary binoculars will pull it in, over in Crux.
Southern sky only. So far south it never rises for most of the northern hemisphere. To see it you'd have to travel to Chile, South Africa or Australia.
Best time of year. It stands highest in the middle of the night around March — 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 0.4) — 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.

Properties

absmag: -11.19
bv: 0.401
constellation: Cru
luminosity: 2606153.55
mag: 8.81
name: HD 109978
spect: O9IV

Nearby objects

About HD 109978

HD 109978 is a rare star. It sits in the constellation Cru, shines at apparent magnitude 8.81 and has spectral type O9IV.

Its spectrum reads O9IV — an O-type star — the hottest, rarest main class there is. Fewer than one star in a million is an O, and none of them lasts long.

How to see it

Look for HD 109978 in the constellation Cru. At apparent magnitude 8.81, it is an easy target for binoculars.

Like any astronomical target, HD 109978 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 109978 is a rare star

HD 109978 scores 42 points on Spacedle's rarity scale, which places it in the rare tier. Another 8 points would lift it into a rarer tier.

That score comes from 4 science badges — Star, Under the Southern Cross, Blazing O-type star and Subgiant (leaving the main sequence) — 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.