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Tau Ophiuchi — Double Star in Ophiuchus

HIP 88404; Tau Ophiuchi; 69 Ophiuchi

Observable Double Star Fair (29/100)

Sep: 1.4", Companion: mag 5.9

Magnitude 5.2m DoubleStar Ophiuchus (Oph) Visible
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1Physical Properties

Magnitude 5.24
Spectral Type F2V
Star Color Yellow-white (B-V 0.38)
Distance 56 ly

2Position & Identifiers

RA 18h 03m 04.9s
Dec -08° 10' 50.0"
Constellation Ophiuchus (Oph)
HR 6734
HIP 88404
HD 164765
Bayer Tau
Flamsteed 69 Oph
Double Cat 11005
SIMBAD Wikipedia

3How easy to split?

Primary 5.2 mag Companion 5.9 mag Separation 1.4″
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Telescope Bortle 3 Bortle 4 Bortle 5
80mm refr. V. hard+ V. hard+ V. hard+
150mm Newt. Hard+ Hard+ Hard+
C8 203mm Medium Medium Medium
Easy Medium Hard Very hard Impossible

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

4Visibility

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Best season May – Jul (peak: Jun)

5Multiple Star System Triple C: optical

Components 3 (triple)
Component IDs AB
Separation 1.4″
Companion Mag 5.9
Companion Sp F5V
Position Angle 292°
Star Colors A: Yellow-white B: Yellow-white
Discoverer STF2262
AB 5.24 F2, 5.94 F3, 280.03y, a = 1.494". Component B is HR 6733. Color for combined light. Spectrum for combined | light, F4IV. C, 11.28V, +0.78(B-V), +0.33(U-B) at 100", optical?

Separation over time

Period: 279.5 y Eccentricity: 0.765 Now: 1.4", PA 293° -0.07" in 5 years
0.00" 0.41" 0.83" 1.2" 1.7" 2025 2030 2035 2040 2045 1.4"

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

Eyepiece View

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80x Dawes: 1.9″ TFOV: 0.6°
Realistic = true angular size
N E 292°

A: 5.2 · B: 5.9 · Sep: 1.4″ · PA: 292° · N up, E right

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

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6

Size Comparison

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8

Spectral Classification

9

Hertzsprung-Russell Diagram

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10

Stellar Lifecycle

11

Blackbody Spectrum

12

Stellar Absorption Spectrum

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

13

Stellar Fusion

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14Stellar Notes

ADS 11005A.
Blended spectra with HR 6733 range from F3 to F5, luminosity III to V.
0.021".
15

Light Travel Time Machine

16

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.

NGC 6539
Easy
Globular cluster — dense ball of ancient stars
Globular Cluster mag 9.6 0.7° Serpens
Y Oph
Medium
Pulsating variable, period 17.1d
Variable Star mag 6.21 3.3° Ophiuchus
NGC 6625
Easy
Open cluster
Open Cluster mag 9.0 6.1° Scutum
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