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Rare variable star 46 EP

HR 3642

RA 136.4099° · Dec -70.5385° · star

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Score breakdown

· 8 badges
46 pts · Rare
Rare 50 pts → Epic
  • Intrinsically luminous (Mv < −2) +10
  • Naked-eye visible +8
  • Hot blue B-type star +6
  • Variable star +5
  • Subgiant (leaving the main sequence) +5
  • Blue-white star +5
  • Gently variable +4
  • A named variable star +3
Total score 46

4 more points to reach Epic.

Badges

  • Variable star · +5
  • Naked-eye visible · +8
  • Hot blue B-type star · +6
  • Subgiant (leaving the main sequence) · +5
  • Blue-white star · +5
  • Intrinsically luminous (Mv < −2) · +10
  • Gently variable · +4
  • A named variable star · +3

Trivia

What it actually is

  • Spectral class. Its spectrum reads B2IVe — a blue-white B-type star, with a surface tens of thousands of degrees hot and a life measured in tens of millions of years.
  • Where it is in life. It is a subgiant, caught in the act of leaving the main sequence as the hydrogen in its core runs out.
  • 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 4.7 you can see it with your own eyes from a dark site, over in Carina.
  • Southern sky only. So far south it never rises for most of the northern hemisphere. To see it you'd have to travel to Chile, South Africa or Australia.
  • Best time of year. It stands highest in the middle of the night around February — that's when to go looking.

Could we get there?

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

Properties

absmag
-2.702
bv
-0.149
constellation
Car
dist ly
967.8219
luminosity
1049.0592
mag
4.66
name
HR 3642
spect
B2IVe
var amplitude
0.1
var designation
V345
var max
4.607
var min
4.707

About HR 3642

HR 3642 is a rare variable star. It lies about 967.8 light-years from Earth, sits in the constellation Car, shines at apparent magnitude 4.66 and has spectral type B2IVe.

Its spectrum reads B2IVe — a blue-white B-type star, with a surface tens of thousands of degrees hot and a life measured in tens of millions of years.

How to see it

Look for HR 3642 in the constellation Car. At apparent magnitude 4.66, it can be glimpsed with the unaided eye under dark skies.

Like any astronomical target, HR 3642 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 3642 is a rare variable star

HR 3642 scores 46 points on Spacedle's rarity scale, which places it in the rare tier. Another 4 points would lift it into a rarer tier.

That score comes from 8 science badges — Variable star, Naked-eye visible, Hot blue B-type star, Subgiant (leaving the main sequence), Blue-white star, Intrinsically luminous (Mv < −2), 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.