Phi Draconis — Double Star in Draco

Magnitude 4.2^m DoubleStar Draco (Dra) Visible

Star Map + List + Plan

Observe

1Physical Properties

Magnitude 4.22

Range 4.21 - 4.24

Period 41.2 hours

Variable Type Alpha2 CVn (Magnetic Rotating)

Spectral Type A0pSi:

Star Color Blue-white (B-V -0.10)

Distance 272 ly

2Position & Identifiers

RA 18h 20m 45.5s

Dec +71° 20' 16.0"

Constellation Draco (Dra)

HR 6920

HIP 89908

HD 170000

SAO 9084

Bayer Phi

Flamsteed 43 Dra

Variable ID Phi Dra

Double Cat 11311

3How easy to split?

Primary 4.2 mag Companion 5.9 mag Separation 0.6″

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

Easy Medium Hard Very hard Impossible

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

To reach "Medium" at Bortle 3, you'd need at least a 380 mm reflector.

4Visibility

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Best season May – Jul (peak: Jun)

5Light Curve

6Multiple Star System Triple

Components 3 (triple)

Component IDs AB

Separation 0.6″

Companion Mag 5.9

Companion Sp B9V

Position Angle 262°

Star Colors A: Blue-white B: Blue-white

Discoverer STT 353

Notes

4.4, 6.1v, 271.7y, a = 0.392".

Separation over time

Period: 307.8 y Eccentricity: 0.752 Now: 0.58", PA 264° + 0.02" 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: 4.2 · B: 5.9 · Sep: 0.6″ · PA: 262° · N up, E right

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

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8

Size Comparison

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9

Compare Stars

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10

Spectral Classification

11

Hertzsprung-Russell Diagram

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Read: The Hertzsprung-Russell Diagram — Reading Stars Like a Map

12

Stellar Lifecycle

13

Blackbody Spectrum

14

Stellar Absorption Spectrum

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

15

Stellar Fusion

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16Stellar Notes

Variable Star

Alpha CV, amp. 0.04V, 1.71646d. Same rotation period.

Spectroscopic Binary

26.768d, K 26.6k/s, V0 -20.8k/s, asini 9.02.

Spectral

Also classified B8Vp.

Dynamical

0.003".

17

Light Travel Time Machine

18

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.

Bright spiral galaxy

Galaxy mag 11.6 1.9° Draco

HIP 86614; Psi1 Draconis; 31 Draconis

Easy double, sep 30.2″

Double Star mag 4.58 3.1° Draco

Small bright planetary nebula

Planetary Nebula mag 9.0 5.1° Draco

Easy double, sep 3.1″

Double Star mag 3.83 7.2° Draco

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