| Observation data Epoch J2000.0 Equinox J2000.0 |
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|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 17m 37.6s |
| Declination | -36° 45' 42" |
| Apparent magnitude (V) | +3.10 |
| Absolute magnitude (V) | -0.20 |
| Distance | 149 ± 6 ly (46 ± 2 pc) |
| Spectral type | M2III |
| Other designations | |
Eta Sagittarii (η Sgr, η Sagittarii) is a star system in the constellation Sagittarius, 149 light years from Earth.
It was formerly known as "Beta Telescopii" (β Tel). The SkyMap site has the name "Sephdar" attributed to η Sgr, but the etymology of this name is not clear.
The primary component, η Sagittarii A, is a spectral type M3.5 red giant. It is a variable star with small magnitude fluctuations between +3.08 and 3.12, and is classified as an irregular variable.
The brightest companion, η Sagittarii B, is spectral class F dwarf star, with an apparent magnitude of +7.77. It is at a distance of 165 astronomical units from the primary and takes approximately 1 300 years to make one orbit. The two stars are separated by 3.6 arcseconds on the sky.
Farther out are two dimmer members of the system, the 13th magnitude η Sagittarii C, separated from A by 33 arcseconds, and the 10th magnitude η Sagittarii D, 93 arcseconds from A.
This star will be in constellation Corona Australis around 6300 AD.[1]
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