About HD 190540
HD 190540 is an uncommon variable star. It sits in the constellation Sgr, shines at apparent magnitude 8.46 and has spectral type G8/K0Vp.
Its spectrum reads G8/K0Vp — a G-type star: the very same spectral class as our own Sun.
Uncommon variable star 33 EP
HD 190540
RA 301.5111° · Dec -18.7044° · star
Score breakdown
· 7 badgesUncommon 34 pts → Rare
- Toward the galactic centre +8
- Sun-like G-type star +8
- Variable star +5
- Gently variable +4
- On the zodiac +3
- A named variable star +3
- Main-sequence star +2
Total score 33
1 more point to reach Rare.
Badges
- Variable star · +5
- Toward the galactic centre · +8
- On the zodiac · +3
- Sun-like G-type star · +8
- Main-sequence star · +2
- Gently variable · +4
- A named variable star · +3
Trivia
Hard to believe
- True brightness. It pours out about 3.5 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 G8/K0Vp — a G-type star: the very same spectral class as our own Sun.
- 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 8.5 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 orange (B−V 1.2) — cooler than the Sun, and the kind of star that burns steadily for tens of billions of years.
By the numbers
- Surface temperature. Its colour puts the surface at roughly 4310 K, against the Sun's 5778 K.
Properties
- absmag
- -11.54
- bv
- 1.201
- constellation
- Sgr
- luminosity
- 3597493.3516
- mag
- 8.46
- name
- HD 190540
- spect
- G8/K0Vp
- var amplitude
- 0.07
- var designation
- V4091
- var max
- 8.429
- var min
- 8.499
Nearby objects
How to see it
Look for HD 190540 in the constellation Sgr. At apparent magnitude 8.46, it is an easy target for binoculars.
Like any astronomical target, HD 190540 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 190540 is an uncommon variable star
HD 190540 scores 33 points on Spacedle's rarity scale, which places it in the uncommon tier. Another 1 point would lift it into a rarer tier.
That score comes from 7 science badges — Variable star, Toward the galactic centre, On the zodiac, Sun-like G-type star, Main-sequence star, 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.