Polis — Double Star in Sagittarius
HIP 89341; Mu Sagittarii; 13 Sagittarii
About Polis
Description
Polis, Mu Sagittarii, is an extremely luminous blue supergiant of spectral class B8 Iab(e) with an estimated distance of approximately 3,000 light-years — not the 36,000 light-years that one catalog parallax reduction has erroneously reported. It is one of the intrinsically brightest stars visible to the naked eye, with an estimated luminosity of around 60,000 Suns. At magnitude 3.86 it is a modest-looking but physically extraordinary member of Sagittarius.
Observing Tips
Polis marks the top of the "teapot" asterism in Sagittarius, north of the main teapot body. In binoculars it is a sharp blue-white point set against a crowded Milky Way background. Best observed June through September.
History
The name Polis comes from the Coptic Egyptian term for the rising star of the Nile flood, later adapted into Greek. The IAU adopted the name in 2017. In Sagittarius, Polis has long been associated with seasonal flood signals in ancient Mediterranean cultures.
Fun Facts
Polis is a classic example of a Be star — an emission-line B supergiant — which occasionally develops circumstellar gas disks detectable in its spectrum. Its enormous intrinsic luminosity means it could be seen from great distances across the galaxy; the star likely has only a few million years left before core collapse.
Observe
1Physical Properties
2Position & Identifiers
3How easy to split?
| Telescope | Bortle 3 | Bortle 4 | Bortle 5 |
|---|---|---|---|
| 80 mm refractor 80mm refr. | Hard+ | Hard+ | Hard |
| 150 mm Newton 150mm Newt. | Easy | Medium+ | Medium+ |
| Celestron C8 (203 mm SCT) C8 203mm | Easy | Easy | Medium+ |
Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs
4Visibility
Set a location in User Settings to see visibility data.
5Light Curve
6Multiple Star System Sextuple
Separation over time
Apparent motion is significant on a human timescale — worth revisiting in a decade.
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
A: 3.9 · B: 10.5 · Sep: 16.9″ · PA: 258° · N up, E right
Resolved · Rayleigh: 2.3″ · Dawes: 1.9″ · Eff: 2.3″
Explore
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Size Comparison
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Compare Stars
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Spectral Classification
11
Hertzsprung-Russell Diagram
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
Discover
16Stellar Notes
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.
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