70 Ophiuchi — Double Star in Ophiuchus
About 70 Oph
Description
70 Ophiuchi is a nearby binary of two K-type main-sequence stars (K0 V + K5 V) about 16.6 light-years away. The pair orbits in a markedly eccentric 88-year orbit, swinging between roughly 1.7″ and 6.7″ apart. Combined visual magnitude is 4.03, with the components at 4.2 and 6.0 — bright enough to study without difficulty.
Observing Tips
Currently around 6.7″ separation (near widest), an easy split at 100×. As the orbit tightens through the 2030s the gap will close to about 1.7″ near 2068, becoming a real test of seeing. The yellow-orange colour contrast is subtle but visible against a dark Ophiuchus background.
History
First catalogued as double by William Herschel in 1779. In the late 19th century Thomas See and others claimed to detect orbital perturbations indicating an unseen massive planet — the announcement was sensational but the supposed planet was eventually shown to be an artefact of measurement error, an early cautionary tale in exoplanet hunting.
Fun Facts
70 Oph's K-dwarf components are about 90 % and 70 % the mass of the Sun, with main-sequence lifetimes far longer than the Sun's — both stars will likely still be shining on the main sequence long after the Sun has evolved into a white dwarf.
Observe
1Physical Properties
2Position & Identifiers
3How easy to split?
| Telescope | Bortle 3 | Bortle 4 | Bortle 5 |
|---|---|---|---|
| 80 mm refractor 80mm refr. | Easy | Easy | Easy |
| 150 mm Newton 150mm Newt. | Easy | Easy | Easy |
| Celestron C8 (203 mm SCT) C8 203mm | Easy | Easy | Easy |
Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs
4Visibility
Set a location in User Settings to see visibility data.
5Multiple Star System 11 components C,D,R,S,T,U,V,Y,Z: optical
Separation over time
Apparent separation over time, computed from ORB6 orbital elements. Steep curves indicate fast-changing pairs — catch them while they're splittable.
Eyepiece View
A: 4.0 · B: 6.2 · Sep: 6.7″ · PA: 118° · N up, E right
Resolved · Rayleigh: 2.3″ · Dawes: 1.9″ · Eff: 2.3″
Explore
7
Size Comparison
8
Compare Stars
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Spectral Classification
10
Hertzsprung-Russell Diagram
11
Stellar Lifecycle
12
Blackbody Spectrum
13
Stellar Absorption Spectrum
Simulated absorption spectrum based on spectral type. Hover over lines to identify elements.
14
Stellar Fusion
Discover
15Stellar Notes
16
Light Travel Time Machine
17
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.
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