Ascella — Double Star in Sagittarius
HIP 93506; Zeta Sagittarii; 38 Sagittarii
About Ascella
Description
Ascella is a white binary star of spectral type A2III+A4IV at magnitude 2.60 in Sagittarius. Located about 89 light-years from Earth, it consists of two A-type stars orbiting each other every 21 years. Ascella forms the base or 'armpit' of the Archer figure and part of the Teapot handle.
Observing Tips
Ascella sits at the bottom of the Teapot handle in Sagittarius. The two components can be resolved in a moderate telescope when near maximum separation. It is a warm white star in the rich Milky Way fields. Best observed July through September.
History
The name Ascella comes from the Latin 'ascella,' meaning 'the armpit,' referring to its position under the Archer's arm. As a relatively nearby bright binary, it has been well-studied since the discovery of its double nature.
Fun Facts
Ascella's two A-type components make it a true physical binary — both stars formed together and orbit their common center of mass. The 21-year orbital period is short enough that the system's orbital motion has been well characterized over decades of observation.
Observe
1Physical Properties
2Position & Identifiers
3How easy to split?
| 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+ |
Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs
4Visibility
Set a location in User Settings to see visibility data.
5Multiple Star System Triple
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: 2.6 · B: 3.5 · Sep: 0.4″ · PA: 133° · N up, E right
Unresolved · Rayleigh: 2.3″ · Dawes: 1.9″ · Eff: 2.3″
Explore
7
Size Comparison
8
Compare Stars
9
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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