Sheliak (Beta Lyrae)
Coordinates, CHARA/Gaia distance (960 ly), 12.94-day eclipsing light curve, rapid orbital period lengthening (+19 s/yr), and guide for Sheliak.
Provenance-Backed Scientific Measurements
Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.
| Parameter | Value | Uncertainty | Method & Epoch | Quality Status | Source Archive |
|---|---|---|---|---|---|
| Visual magnitude range (V) | 3.52 mag | ± 0.45 mag | Photoelectric V-band photometry (3.25 at max, 4.36 at primary eclipse, 3.82 at secondary eclipse) | definitive | Hipparcos New Reduction Catalog |
| Eclipsing orbital period (lengthening by 19 s/yr) | 12.9414 d | ± 0.0005 d | O−C eclipse timing (increased from 12.89 d in 1784 to 12.94 d today due to 2 × 10^-5 M☉/yr mass transfer) | definitive | SIMBAD Astronomical Database (CDS) |
| System distance (CHARA orbital parallax + Gaia DR3) | 295 pc | ± 15 pc | CHARA interferometric orbit (Zhao et al. 2008 / Mourard et al. 2018) + Gaia DR3 (~960 ± 50 ly) (J2016.0) | definitive | ESA Gaia Archive — Data Release 3 |
| Gainer star mass (shrouded B0.5 V primary) | 13.16 M☉ | ± 0.3 M☉ | CHARA resolved orbit + radial velocity (Roche-filling B6–8 II donor = 2.97 ± 0.2 M☉) | definitive | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Sheliak (Beta Lyrae Mass-Transfer Binary) at RA 18h 50m 04.80s, Dec +33° 21′ 45.6″ within Lyra, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.
Astrophysical Context & Structure
Sheliak (Beta Lyrae, from the Arabic al-Shilyāq meaning 'the Tortoise-shell Lyre'), marking the southwestern corner of the Lyra parallelogram just south of the Ring Nebula (M57), is the prototype of the Beta Lyrae (EB) class of eclipsing binary stars. Discovered to vary by John Goodricke in September 1784—the very same month he discovered Delta Cephei—Sheliak never stays at constant brightness: over its 12.9414-day orbital cycle, its brightness rises and falls continuously between magnitude 3.25 at quadrature, 4.36 at primary minimum, and 3.82 at secondary minimum because the stars are tidally stretched into teardrops.
Located 295 ± 15 parsecs (960 light-years) away and directly resolved into images by the CHARA optical interferometer, Beta Lyrae is caught in the middle of rapid, ongoing Roche-lobe mass transfer. The visibly brighter star (a B6–8 II bright giant now stripped down to 2.97 solar masses) overflows its Roche lobe and dumps roughly 2 × 10^-5 solar masses per year (nearly 7 Earth masses every year!) onto its companion, which has now grown to 13.16 solar masses.
Because that mass transfer flows from the less massive star to the more massive star, conservation of angular momentum forces the two stars apart and causes Beta Lyrae's orbital period to lengthen by a staggering 19 seconds every single year—accumulating over an hour of delay since Goodricke's 1784 discovery! The 13.2-solar-mass gainer is completely hidden inside a thick, 60-solar-radius glowing accretion disk and bipolar jet.
Practical Visual Observing Guide
- Ideal naked-eye variable star for beginners: right next to Sheliak (1.8° east at the southeastern corner of Lyra) sits Sulafat (Gamma Lyrae), a steady magnitude 3.25 star that matches Sheliak's maximum brightness!
- Compare Sheliak to Sulafat (mag 3.25) and Zeta Lyrae (mag 4.36) on successive clear nights to watch the 12.94-day continuous eclipsing wave with the unaided eye.
- In any small 50–80 mm telescope at 30×–60×, Sheliak is also a picturesque multiple star: 45.7 arcseconds south sits magnitude 7.2 Beta Lyrae B (a B7 V star), along with 9.9-mag Component E (67″) and 10.6-mag Component F (86″).
Catalog Cross-Identifications & Aliases
Common Aliases: β Lyrae · Sheliak · HD 174638 · HIP 92420 · 10 Lyrae
| Catalog Authority | Identifier |
|---|---|
| GAIADR3 | 2090521258478158080 |
| HIP | HIP 92420 |
| HD | HD 174638 |
| SIMBAD | * bet Lyr |
| WIKIDATA | Q13054 |
Related Objects, Comparisons & Guides
Vega (Alpha Lyrae Zero-Point Star)
Coordinates, distance (25.04 ly), magnitude 0.03 photometric zero point, rapid oblate rotation, and observing guide for Vega in Lyra.
Algol (Beta Persei Eclipsing Binary)
Coordinates, Hipparcos distance (90 ly), 2.8673-day eclipse cycle, Algol Paradox mass transfer, and visual timing guide for Algol.
Epsilon Lyrae (The Double Double Star)
Coordinates, Gaia DR3 distance (160 ly), 208″ wide pair and 2.3″/2.4″ tight sub-pairs, and telescope resolution test guide for Epsilon Lyrae.
Apparent vs Absolute Magnitude Explained
Understand the logarithmic Pogson astronomical magnitude scale, apparent visual magnitude (m), absolute magnitude (M at 10 parsecs), and bolometric corrections.
Angular Size, Separation & Field of View
How angular diameter (degrees, arcminutes, arcseconds), spherical angular separation, and small-angle physical diameter relate to telescope field of view.
Scientific Sources & Dataset Provenance
- ESA Gaia Archive — Data Release 3 (DR3 (2022-06-13)): Gaia Collaboration, Vallenari, A., et al. 2023, A&A, 674, A1 (Gaia Data Release 3) — European Space Agency / Gaia DPAC
- Hipparcos New Reduction Catalog (2007 New Reduction): van Leeuwen, F. 2007, A&A, 474, 653 (Validation of the new Hipparcos reduction) — ESA / van Leeuwen (2007)
- SIMBAD Astronomical Database (CDS) (2026-10 release): Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database) — Centre de Données astronomiques de Strasbourg