Betelgeuse

Overview

A changing supergiant

Betelgeuse, Alpha Orionis and HD 39801, is a red supergiant in Orion. Structure and variability in its photosphere complicate the assignment of a single edge, distance or size. Molecular layers and dust also affect what observers see. A size-comparison value represents one determination, rather than a rigid sphere with permanently fixed dimensions.

The adopted radius and its uncertainty

We adopt Joyce and colleagues’ 2020 result: 764 solar radii, with limits of −62 and +116. Table 2 identifies this as a 3σ interval derived from seismic models, not the standard error of a direct image. The study combines stellar evolution, oscillation analysis and hydrodynamics. Its reference temperature of 3,600 ± 25 K comes from a spectroscopic determination near the brightness minimum; modeling extends the temperature allowance to ±200 K. Those two uncertainties serve different purposes and must not be interchanged.

Different distance determinations

The same table obtains 168.1 parsecs, with limits of −14.9 and +27.5 at 3σ, by combining the seismic radius with an adopted angular diameter. The historical HYG astrometry retained here uses another solution. The paper also compares different optical and radio estimates. We do not average these results or attribute the model distance to HYG: their assumptions and error budgets differ.

The Great Dimming

Betelgeuse faded in visible light in late 2019 and early 2020. Observations with SPHERE and GRAVITY described by ESO in 2021 support dust formation near a cooled surface region. NASA’s 2022 account describes recovery after a surface mass ejection. That event did not confirm an imminent supernova. These are dated interpretations of a historical episode, not measurements of today’s brightness or a prediction of the time of the star’s demise.

Interpreting the catalogue

The atlas retains the historical HYG distance of 152.6718 parsecs and its reference coordinates. That record, the catalogue spectral classification and the adopted research parameters come from different solutions. Positions have not been recalculated and one distance has not been substituted for another. The compared sizes are radii, not diameters; a scale illustration does not show present-day position or brightness.

Sources and references