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V389 Cygni — Double Star in Cygnus

Observable Double Star Good (58/100)

Sep: 3.3", Companion: mag 8.1

Magnitude 5.5–5.7m DoubleStar Cygnus (Cyg) Visible
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1Physical Properties

Magnitude 5.59
Range 5.55 - 5.71
Period 34.3 hours
Variable Type Slowly Pulsating B Star
Spectral Type B9VpSi
Star Color Blue-white (B-V -0.10)

2Position & Identifiers

RA 21h 08m 38.9s
Dec +30° 12' 21.0"
Constellation Cygnus (Cyg)
HR 8094
HIP 104371
HD 201433
SAO 70968
Variable ID V389 Cyg
Double Cat 14682
SIMBAD

3How easy to split?

Primary 5.6 mag Companion 8.1 mag Separation 3.3″
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Telescope Bortle 3 Bortle 4 Bortle 5
80mm refr. Medium Medium Medium
150mm Newt. Easy Easy Easy
C8 203mm Easy Easy Easy
Easy Medium Hard Very hard Impossible

Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs

4Visibility

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Best season Jul – Sep (peak: Aug)

5Light Curve

6Multiple Star System Quadruple C,D: optical

Components 4 (quadruple)
Component IDs AB
Separation 3.3″
Companion Mag 8.1
Position Angle 303°
Star Colors A: Blue-white B: Yellow-white
Discoverer STF2762
AB binary. B, 7.8v A0V or Am(A2.5/A7V/A9), vsini 80k/s. C, 9.2v K1III at 58" optical, vsini =<54k/s.

Separation over time

Measured 1783 → 2023 (240 y)
Separation drift 4.0" → 3.3" (-0.70")
Rate -0.0029" / y
PA drift 315° → 303° (-12°, -0.050°/y)

Essentially fixed on human timescales — the same view your grandchildren will see.

Measured from the WDS observational archive. No orbital solution has been derived — most likely the period is too long to fit an orbit to the available measurement arc.

Eyepiece View

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80x Dawes: 1.9″ TFOV: 0.6°
Realistic = true angular size
N E 303°

A: 5.6 · B: 8.1 · Sep: 3.3″ · PA: 303° · N up, E right

Resolved · Rayleigh: 2.3″ · Dawes: 1.9″ · Eff: 2.3″

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7

Size Comparison

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9

Spectral Classification

10

Hertzsprung-Russell Diagram

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11

Stellar Lifecycle

12

Blackbody Spectrum

13

Stellar Absorption Spectrum

Simulated absorption spectrum based on spectral type. Hover over lines to identify elements.

14

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15Stellar Notes

ADS 14682A, 5.55 - 5.71V. Alternating periods of 1.12912 and 1.19328d. V 389 Cyg may be triple star, with long period | about 150d, perhaps 110 or 270d.
ADS 14682A, 3.3132d, K 20.2k/s, V0 -22.1k/s, asini 0.920. Also about 150d, possibly 110 or 270d.
0.008".

Nearby in the Sky

Other targets within a few degrees — pan your scope a little and keep exploring.

Visibility scores assume a 150 mm Newton at Bortle 4.

DT Cyg
Hard+
Pulsating variable, period 2.5d
Variable Star mag 5.82 1.1° Cygnus
NGC 7013
Hard+
Bright spiral galaxy
Galaxy mag 12.0 1.1° Cygnus
Network nebula
NGC 6995
Medium+
Supernova remnant
Supernova Remnant mag 7.00 2.7° Cygnus
49 Cyg
Medium+
Tight double — a rewarding split at 2.8″
Double Star mag 5.51 6.3° Cygnus
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