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Rare variable star 40 EP

HD 209879

RA 331.6874° · Dec -15.6445° · star

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Score breakdown

· 7 badges
40 pts · Rare
Rare 50 pts → Epic
  • Strongly variable +10
  • Deep red star +8
  • Giant star +6
  • Variable star +5
  • Cool red M-type star +5
  • On the zodiac +3
  • A named variable star +3
Total score 40

10 more points to reach Epic.

Badges

  • Variable star · +5
  • On the zodiac · +3
  • Cool red M-type star · +5
  • Giant star · +6
  • Deep red star · +8
  • Strongly variable · +10
  • A named variable star · +3

Trivia

Hard to believe

  • True brightness. It pours out about 963.8 thousand 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 M3III: — an M-type red star — and M stars are the silent majority: roughly three of every four stars in the galaxy are one.
  • Where it is in life. It is a giant. It has already exhausted its core hydrogen and swollen up enormously in response.
  • 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 9.9 you'll want a small backyard telescope, over in Aquarius.
  • 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 August — that's when to go looking.

Its true colour

  • Its true colour. Measured through blue and visual filters it comes out deep orange-red (B−V 1.5) — one of the coolest surfaces a star can have while still fusing.

Properties

absmag
-10.13
bv
1.541
constellation
Aqr
luminosity
981747.943
mag
9.87
name
HD 209879
spect
M3III:
var amplitude
0.53
var designation
BM
var max
9.615
var min
10.145

About HD 209879

HD 209879 is a rare variable star. It sits in the constellation Aqr, shines at apparent magnitude 9.87 and has spectral type M3III:.

Its spectrum reads M3III: — an M-type red star — and M stars are the silent majority: roughly three of every four stars in the galaxy are one.

How to see it

Look for HD 209879 in the constellation Aqr. At apparent magnitude 9.87, a small backyard telescope will bring it into view.

Like any astronomical target, HD 209879 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 209879 is a rare variable star

HD 209879 scores 40 points on Spacedle's rarity scale, which places it in the rare tier. Another 10 points would lift it into a rarer tier.

That score comes from 7 science badges — Variable star, On the zodiac, Cool red M-type star, Giant star, Deep red star, Strongly 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.