About HD 21705
HD 21705 is a common star. It sits in the constellation Eri, shines at apparent magnitude 8.99 and has spectral type G8III/IV.
Its spectrum reads G8III/IV — a G-type star: the very same spectral class as our own Sun.
Common star 17 EP
HD 21705
RA 52.1390° · Dec -41.6085° · star
Score breakdown
· 3 badgesCommon 22 pts → Uncommon
- Sun-like G-type star +8
- Giant star +6
- Star +3
Total score 17
5 more points to reach Uncommon.
Badges
- Star · +3
- Sun-like G-type star · +8
- Giant star · +6
Trivia
Hard to believe
- True brightness. It pours out about 2.2 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 G8III/IV — a G-type star: the very same spectral class as our own Sun.
- 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 9 it is just past naked-eye reach — ordinary binoculars will pull it in, over in Eridanus.
- 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 November — 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.
Properties
- absmag
- -11.01
- bv
- 0.945
- constellation
- Eri
- luminosity
- 2208004.733
- mag
- 8.99
- name
- HD 21705
- spect
- G8III/IV
How to see it
Look for HD 21705 in the constellation Eri. At apparent magnitude 8.99, it is an easy target for binoculars.
Like any astronomical target, HD 21705 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 21705 is a common star
HD 21705 scores 17 points on Spacedle's rarity scale, which places it in the common tier. Another 5 points would lift it into a rarer tier.
That score comes from 3 science badges — Star, Sun-like G-type star and Giant 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.