Vega vs Arcturus Bright Star Comparison
Compare northern zero-magnitude beacons Vega (Alpha Lyrae, A0 V) and Arcturus (Alpha Bootis, K1.5 III) in temperature, disk radius, and kinematics.
Compared Celestial Objects
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.
Constellation: Lyra · Coords: 18h 36m 56.34s, +38° 47′ 01.3″
Arcturus (Alpha Bootis Red Giant)
Coordinates, Hipparcos distance (36.7 ly), magnitude −0.05, halo-stream kinematics, and observing guide for Arcturus in Boötes.
Constellation: Boötes · Coords: 14h 15m 39.67s, +19° 10′ 56.7″
Normalized Shared Parameter Table
| Parameter | Unit / Scale | Vega (Alpha Lyrae Zero-Point Star) | Arcturus (Alpha Bootis Red Giant) |
|---|---|---|---|
| Apparent Visual Magnitude (V) | mag | +0.026 ± 0.008 | −0.050 ± 0.010 |
| Heliocentric Distance | pc | 7.678 ± 0.008 pc (25.04 ly) | 11.26 ± 0.02 pc (36.72 ly) |
| Effective Temperature (Teff) | K | 9,602 ± 180 K (A0 Va) | 4,286 ± 30 K (K1.5 IIIpe) |
| Photospheric Radius | R☉ | 2.362 × 2.818 R☉ (oblate) | 25.4 ± 0.2 R☉ |
| Bolometric Luminosity | L☉ | 40.12 ± 0.45 L☉ | 170 ± 7 L☉ |
Astrophysical & Observational Synthesis
Sharing the northern spring and summer sky at almost identical zero-magnitude visual brightness, Vega and Arcturus illustrate two opposite eras of Galactic history. Vega is a 455-million-year-old, 2.1-solar-mass main-sequence star rotating near 88% of its breakup speed (flattening its poles to 9,988 K and bulging its equator to 7,600 K), surrounded by a cold dusty debris disk and defining the classical B−V = 0.00 photometric zero point.
Arcturus (Alpha Boötis), although slightly less massive than the Sun (~1.08 M☉), is a 7.1-billion-year-old red giant that has exhausted its core hydrogen and swollen to 25.4 solar radii. Despite its cooler 4,286 K orange photosphere (B−V = +1.23), Arcturus's 100-fold larger surface area radiates 170 solar luminosities—more than four times Vega's total energy output.
Kinematically, Vega moves calmly within the young Galactic thin disk, whereas metal-poor Arcturus ([Fe/H] = −0.52 dex) plunges nearly perpendicularly through the solar neighborhood at 122 km/s (proper motion 2.28 arcseconds/year) as the leading member of the ancient Arcturus Halo Stream.
Related Reference Guides
Stellar Spectral Classification (OBAFGKM)
Reference guide to Morgan-Keenan (MK) stellar classification (O B A F G K M), luminosity classes (I–V, WD), color index (B-V), and the H-R diagram.
Proper Motion, Radial Velocity & Redshift
How astronomers combine tangential proper motion (mas/yr), Doppler radial velocity (km/s), and cosmological redshift (z) to reconstruct 3D space motion.
Primary Catalogs & Scientific Sources
- 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
- 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
- Revised New General Catalogue and Index Catalogue (RNGC/IC) (2024/2026 edition): Steinicke, W. 2010, Observing and Cataloguing Nebulae and Star Clusters (Cambridge Univ. Press); Verga, M. OpenNGC (CC-BY-SA 4.0 / data tables) — Wolfgang Steinicke / OpenNGC