HIP 105390 — Double Star in Cygnus

Observable Double Star Good (56/100)

Sep: 2.5", Companion: mag 7.4

Magnitude 5.7^m DoubleStar Cygnus (Cyg) Visible

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Observe

1Physical Properties

Magnitude 5.68

Spectral Type G8IV subgiant

Star Color Orange (B-V 1.08)

Distance 181 ly

2Position & Identifiers

RA 21h 20m 50.1s

Dec +32° 27' 10.0"

Constellation Cygnus (Cyg)

HR 8166

HIP 105390

HD 203358

SAO 71230

Double Cat 14889

3How easy to split?

Primary 5.7 mag Companion 7.4 mag Separation 2.5″

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Telescope	Bortle 3	Bortle 4	Bortle 5
80 mm refractor 80mm refr.	Hard+	Hard+	Hard+
150 mm Newton 150mm Newt.	Easy	Easy	Easy
Celestron C8 (203 mm SCT) 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)

5Multiple Star System Triple C: optical

Components 3 (triple)

Component IDs AB

Separation 2.5″

Companion Mag 7.4

Position Angle 17°

Star Colors A: Orange

Discoverer STT 437

Notes

AB binary. Component B, G5IV.

Separation over time

Period: 1218.1 y Eccentricity: 0.501 Now: 2.5", PA 18° + 0.01" in 5 years

Apparent separation over time, computed from ORB6 orbital elements. Steep curves indicate fast-changing pairs — catch them while they're splittable.

Eyepiece View

Telescope Eyepiece

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80x Dawes: 1.9″ TFOV: 0.6°

Seeing

Scale Realistic = true angular size

A: 5.7 · B: 7.4 · Sep: 2.5″ · PA: 17° · N up, E right

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

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Size Comparison

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Spectral Classification

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Hertzsprung-Russell Diagram

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Stellar Lifecycle

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Blackbody Spectrum

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Stellar Absorption Spectrum

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

13

Stellar Fusion

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Light Travel Time Machine

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Relativistic Travel

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.

Pulsating variable, period 2.5d

Variable Star mag 5.82 3.3° Cygnus

Easy double, sep 3.3″

Double Star mag 5.59 3.4° Cygnus

Open Cluster mag 7.0 4.1° Cygnus

Elliptical galaxy

Galaxy mag 13.0 4.2° Cygnus

Mu Cyg (BS8309)

Tight double — a rewarding split at 1.4″

Double Star mag 4.73 6.2° Cygnus

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