Theta Lyrae
Star in a trinary star system in the constellation Lyra
From Wikipedia, the free encyclopedia
Theta Lyrae (θ Lyr), also named Ninnisig,[6] is a red giant star in the constellation Lyra, approximately 760 light-years away from Earth.
 | |
| Observation data Epoch J2000.0 Equinox ICRS | |
|---|---|
| Constellation | Lyra |
| Right ascension | 19h 16m 22.0951s[1] |
| Declination | +38° 08′ 01.431″[1] |
| Apparent magnitude (V) | 4.38[2] |
| Characteristics | |
| Spectral type | K0II[3] |
| U−B color index | +1.23[2] |
| B−V color index | +1.26[2] |
| Astrometry | |
| Radial velocity (Rv) | −31.05±0.14[1] km/s |
| Proper motion (μ) | RA: −2.864 mas/yr[1] Dec.: 4.114 mas/yr[1] |
| Parallax (π) | 4.2005±0.1053 mas[1] |
| Distance | 755.9+21.9 −20.2 ly (237.9+6.7 −6.2 pc)[4] |
| Absolute magnitude (MV) | −2.76+0.27 −0.24[3] |
| Details | |
| Radius | 60.31+1.92 −2.99[5] R☉ |
| Luminosity | 1,374±43[5] L☉ |
| Surface gravity (log g) | 1.93[3] cgs |
| Temperature | 4,523±44[5] K |
| Metallicity [Fe/H] | −0.01[3] dex |
| Rotational velocity (v sin i) | 3.6±1.4[3] km/s |
| Other designations | |
| Ninnisig[6], θ Lyr, 21 Lyr, BD+37°3398, GC 26585, HD 180809, HIP 94713, HR 7314, SAO 68065, GSC 03121-02287, IDS 19129+3757 A[7] | |
| Database references | |
| SIMBAD | data |
Theta Lyrae is an orange bright giant star of the spectral type K0II, which means that it possesses a surface temperature of about 5,000 K, and is many times bigger and brighter, yet cooler, than the Sun.
Ninnisig and Erragal are two ancient Sumerian deities associated with a pair of stars, identified as Theta Lyrae and Eta Lyrae (Aladfar).[8] The IAU Working Group on Star Names adopted the name Ninnisig for this star on 18 June 2026.[6]
BD+37°3399 and BD+37°3399B are respectively 10th- and 11th-magnitude companions, although not at the same distance. BD+37°3399 is a giant star with a spectral type of K2III. It is therefore almost the same temperature as Theta Lyrae.[9] BD+37° 3399B is an 11th magnitude star of an unknown spectral type.[10]