UY Scuti (BD−12 5055)
Coordinates, revised Gaia DR3 distance (~1.55 kpc vs older 2.9 kpc), ~755–909 R☉ radius revision, 740-day pulsation, and guide for UY Scuti.
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, heavily reddened) | 9 mag | ± 0.7 mag | AAVSO V-band monitoring (oscillates between V = 8.29 and 10.56; K-band = +1.19 mag) | definitive | SIMBAD Astronomical Database (CDS) |
| Trigonometric distance (Gaia DR3) | 1550 pc | ± 190 pc | Gaia DR3 parallax (0.643 ± 0.081 mas / ~5,060 ly; earlier 2013 spectro-extinction estimate was 2,900 ± 317 pc) (J2016.0) | disputed | ESA Gaia Archive — Data Release 3 |
| Photospheric radius (at Gaia DR3 distance) | 909 R☉ | ± 115 R☉ | VLTI/AMBER Rosseland angular diameter (5.48 ± 0.10 mas) at 1.55 kpc (1,708 R☉ at older 2.9 kpc) | disputed | SIMBAD Astronomical Database (CDS) |
| Semiregular pulsation period | 740 d | ± 30 d | Optical & near-IR long-term photometry | high-confidence | SIMBAD Astronomical Database (CDS) |
| Effective temperature | 3365 K | ± 134 K | VLTI/AMBER K-band spectroscopy & MARCS atmospheric modeling | high-confidence | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots UY Scuti (Pulsating Red Supergiant in Scutum) at RA 18h 27m 36.58s, Dec -12° 27′ 58.9″ within Scutum, 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
UY Scuti (BD−12 5055), a dusty M2–M4 Ia red supergiant pulsating with a ~740-day period in the northern part of the constellation Scutum, became famous worldwide in 2013 when VLTI/AMBER near-infrared interferometry measured its Rosseland-mean angular diameter at 5.48 ± 0.10 milliarcseconds. Adopting a 1970s spectroscopic distance estimate of 2.9 ± 0.3 kiloparsecs (~9,500 light-years), astronomers derived a linear radius of 1,708 ± 192 solar radii (~7.9 AU, beyond the orbit of Jupiter), briefly crowning UY Scuti as the largest measured star in the Milky Way.
However, space astrometry from the Gaia mission (Gaia DR2 and DR3) subsequently measured UY Scuti's trigonometric parallax directly at 0.643 ± 0.081 milliarcseconds, placing the star much closer to Earth at ~1.55 ± 0.19 kiloparsecs (~5,060 light-years, or ~1.8 kpc with zero-point corrections). Because linear radius equals angular diameter multiplied by distance, halving UY Scuti's distance revises its physical radius down to ~909 ± 115 solar radii (~4.2 AU)—still a titanic red supergiant capable of engulfing Mars and the asteroid belt, but smaller than hypergiants like VY Canis Majoris (~1,420 R☉) and Stephenson 2 DFK 1.
Even at its revised Gaia distance, UY Scuti radiates roughly 97,000 to 125,000 solar luminosities at a cool effective temperature of 3,365 K and sheds more than 5 × 10^-5 solar masses per year into a dense silicate dust shell that dims its visual light by over 3 magnitudes.
Practical Visual Observing Guide
- Located in northwestern Scutum ~2° north-northwest of the Eagle Nebula (Messier 16), right on the edge of the Scutum Star Cloud.
- Because interstellar and circumstellar dust extinguish its visible light while letting infrared pass freely, UY Scuti shines at magnitude 8.3 to 10.6 Visually (easily seen as a deep crimson-orange star in any 80–100 mm telescope at 60×–100×) while blazing at magnitude +1.19 in the 2.2-micron K band!
Catalog Cross-Identifications & Aliases
Common Aliases: BD-12 5055 · IRC -10422 · RAFGL 2162
| Catalog Authority | Identifier |
|---|---|
| GAIADR3 | 4152920616791426432 |
| SIMBAD | V* UY Sct |
| WIKIDATA | Q1390159 |
Related Objects, Comparisons & Guides
VY Canis Majoris (Extreme Red Hypergiant)
Coordinates, VLBA maser parallax distance (1.17 kpc), 1,420 R☉ hypergiant radius, asymmetric mass-loss arcs, and guide for VY Canis Majoris.
Garnet Star (Mu Cephei Red Supergiant)
Coordinates, Cepheus OB2 distance (~940 pc / 3,060 ly), magnitude 4.08, ~970 R☉ radius, and visual color guide for Herschel's Garnet Star.
Betelgeuse (Alpha Orionis Red Supergiant)
Coordinates, competing optical vs radio distances (168 vs 222 pc), radius, Great Dimming physics, and observing guide for Betelgeuse.
Measurement Uncertainty & Optics in Astronomy
How random vs systematic errors, asymmetric error bars, model dependencies, and optical aperture/exit-pupil limits shape astronomical measurements.
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
- 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