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Rare variable star 47 EP

HR 4739

RA 186.8703° · Dec -58.9918° · star

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Score breakdown

· 8 badges
47 pts · Rare
Rare 50 pts → Epic
  • Naked-eye visible +8
  • Under the Southern Cross +8
  • Deep red star +8
  • Giant star +6
  • Variable star +5
  • Cool red M-type star +5
  • Gently variable +4
  • A named variable star +3
Total score 47

3 more points to reach Epic.

Badges

  • Variable star · +5
  • Naked-eye visible · +8
  • Under the Southern Cross · +8
  • Cool red M-type star · +5
  • Giant star · +6
  • Deep red star · +8
  • Gently variable · +4
  • A named variable star · +3

Trivia

What it actually is

  • Spectral class. Its spectrum reads M4/M5III — an M-type red star — and M stars are the silent majority: roughly three of every four stars in the galaxy are one.
  • 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.

Sense of scale

  • In perspective. Far away by human standards, yet still a local address inside the Milky Way's spiral arms.

Find it in the sky

  • How to spot it. At magnitude 5.4 you can see it with your own eyes from a dark site, over in Crux.
  • 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 March — that's when to go looking.

Could we get there?

  • Verdict. Hopelessly far for any craft humanity can build today.

Getting there

  • Aboard Voyager 1. ≈ 7.8 million years at Voyager 1's speed (17 km/s).

Properties

absmag
-0.286
bv
1.543
constellation
Cru
dist ly
443.1469
luminosity
113.3444
mag
5.38
name
HR 4739
spect
M4/M5III
var amplitude
0.33
var designation
BL
var max
5.24
var min
5.57

About HR 4739

HR 4739 is a rare variable star. It lies about 443.1 light-years from Earth, sits in the constellation Cru, shines at apparent magnitude 5.38 and has spectral type M4/M5III.

Its spectrum reads M4/M5III — 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 HR 4739 in the constellation Cru. At apparent magnitude 5.38, it can be glimpsed with the unaided eye under dark skies.

Like any astronomical target, HR 4739 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 HR 4739 is a rare variable star

HR 4739 scores 47 points on Spacedle's rarity scale, which places it in the rare tier. Another 3 points would lift it into a rarer tier.

That score comes from 8 science badges — Variable star, Naked-eye visible, Under the Southern Cross, Cool red M-type star, Giant star, Deep red 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.