About HD 173409
HD 173409 is a rare star. It sits in the constellation Sgr, shines at apparent magnitude 9.54 and has spectral type C.
Its spectrum reads C — a carbon star, wrapped in so much soot that its light is filtered to a deep ruby red.
Rare star 38 EP
HD 173409
RA 281.6109° · Dec -31.3422° · star
Score breakdown
· 4 badgesRare 50 pts → Epic
- Carbon star (sooty red) +24
- Toward the galactic centre +8
- Star +3
- On the zodiac +3
Total score 38
12 more points to reach Epic.
Badges
- Star · +3
- Toward the galactic centre · +8
- On the zodiac · +3
- Carbon star (sooty red) · +24
Trivia
Hard to believe
- True brightness. It pours out about 1.3 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 C — a carbon star, wrapped in so much soot that its light is filtered to a deep ruby red.
Find it in the sky
- How to spot it. At magnitude 9.5 you'll want a small backyard telescope, 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 orange (B−V 0.9) — cooler than the Sun, and the kind of star that burns steadily for tens of billions of years.
- 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 5020 K, against the Sun's 5778 K.
Properties
- absmag
- -10.46
- bv
- 0.89
- constellation
- Sgr
- luminosity
- 1330454.418
- mag
- 9.54
- name
- HD 173409
- spect
- C
How to see it
Look for HD 173409 in the constellation Sgr. At apparent magnitude 9.54, a small backyard telescope will bring it into view.
Like any astronomical target, HD 173409 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 173409 is a rare star
HD 173409 scores 38 points on Spacedle's rarity scale, which places it in the rare tier. Another 12 points would lift it into a rarer tier.
That score comes from 4 science badges — Star, Toward the galactic centre, On the zodiac and Carbon star (sooty red) — 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.