Betelgeuse

STARM1-M2Ia-Iab red supergiant

ALMA (ESO/NAOJ/NRAO)/E. O’Gorman/P. Kervella CC BY 4.0

[

OVERVIEW

] STAR

Betelgeuse is an in the constellation Orion, 497.9 from Earth, shining at apparent magnitude 0.45 (). Other catalogues list it as 58 α Ori, HD 39801 and HIP 27989, among 6 designations in total. It has been known since antiquity.

A dying red supergiant so large it would engulf Jupiter if placed at the Sun. It will explode as a supernova — sometime in the next hundred thousand years.

WHAT IT IS: Red supergiant
HOW FAR: 497.9
HOW BRIGHT (V)
WHERE TO LOOK: Orion

[

THE MODEL

] RADIUS FROM THE LUMINOSITY AND THE TEMPERATURE

DRAG TO ORBIT

CALCULATED · NOT AN OBSERVATION · RADIUS FROM THE LUMINOSITY AND THE TEMPERATURE · MEASURED TEMPERATURE · 3540 K · 13 400 L☉ · VARIABLE, MAG 0.28–0.57 · PERIOD 2335 DAYS · SPOTS OVER 0.14% OF IT · CHROMOSPHERE, NO CORONA AND NO FLARES

Drawn from the radius from the luminosity and the temperature and from the same properties the picture at the top of this page uses, at the distance a flight to it would stop. It is cool enough to convect at the surface, so it has a magnetic field wound by that convection, and the field is what everything else here comes from: the dark patches are places where it is strong enough to stop the heat arriving, so they are cooler rather than merely darker, and they are drawn at the fraction of the surface a star this active is measured to cover. The bright web between them is the same field swept to the edges of the larger convection cells, and the brighter patches beside the spots are that web bundled up — both of them brighter towards the limb, because what makes them bright is seeing down the wall of a magnetic tube rather than into its mouth. The fringe standing off the edge is the chromosphere, a forest of jets a few hundred kilometres wide, and the flames leaning out of it are prominences: chromospheric gas held up by the field, drawn at the height one reaches and the width one has. What it does not have is a corona: past about the middle of class K a giant has a chromosphere and a slow, cool, massive wind where a dwarf has a million-kelvin corona, and the ultraviolet spectra show the line sharply. Nor does it flare, for the same reason — there is no coronal gas for the field to heat. Drag it, or use the arrow keys, to look from another direction. The stars behind are the 498,631 this catalogue holds real distances for, at their real positions and drawn from where the camera actually is — so the constellations are wrong, and that is the point. This is the sky from there, not the sky from here.

[

IMAGES

] 4 FRAMES

ALMA (ESO/NAOJ/NRAO)/E. O’Gorman/P. Kervella
CC BY 4.0
Adam Block/Steward Observatory/University of Arizona
CC BY-SA 3.0
ESO/P. Kervella
CC BY 4.0
ESO/P. Kervella
CC BY 4.0

[

OBSERVING

] FROM WHERE YOU ARE

What it takes to see Betelgeuse for yourself. Everything in this part of the page is worked out for a real horizon, a real night and the equipment you say you have.

TONIGHT

Say where you are, and this line says when Betelgeuse is worth going out for.

VIEW IN SKY MAP FLY TO BETELGEUSE

[

THROUGH AN EYEPIECE

] 150 MM TELESCOPE · 25 MM EYEPIECE

10′ ACROSS

Bright enough to pick out with your eyes alone, and from a lit street as well as a dark one. Its brightest companion sits 2.9′ away, which at 48× is cleanly split.

: 48×
: 1.08
: 1.25
: 13.0
· AE: 2.9 · cleanly split
· AH: 4.0 · cleanly split
· AF: 2.8 · cleanly split
APPARENT MAGNITUDE (): 0.45 · within reach

A is where the pair was the year it was measured — the ones above, between 1983 and 2023, and a pair in a real orbit has moved since. The brightest companion — AE — is 10.6 magnitudes down on the star itself, which this far out from it is a faint speck beside a bright star rather than a matched pair.

FIND IT ON THE SKY MAP ↗

[

APPARENT PLACE

] EQUINOX J2026.7

Where a telescope has to be pointed today, which is not quite where the catalogue records the object: the coordinate grid itself has turned since the year 2000 the catalogue is referred to.

RIGHT ASCENSION
DECLINATION
GRID TURNED SINCE: 21.6
PROPER MOTION SINCE: 0.78

Computed for 2026-09-11 00:00 UT. Two things separate it from the catalogued position above: Betelgeuse has moved under its own proper motion, and the coordinate grid has turned under it — about fifty arcseconds a year of precession since 2000, and the small nodding of the Earth’s axis on top of that. Aberration and refraction are not included, and neither is parallax; each is under an arcminute, which is also about as well as the catalogued position is known. The same figure for any date.

[

VARIABILITY

] SEMIREGULAR PULSATING SUPERGIANT

RANGE, AS SAMPLED: 0.28 – 0.57
PERIOD: 2335 days (6.39 years)

For this class the published period is a mean cycle time rather than an ephemeris: the star repeats on that timescale without keeping to it, so counting cycles from a past event would predict a date the star has no obligation to meet.

The range is the spread the Hipparcos satellite measured, converted to the visual scale. It is approximate: the satellite sampled the star on a schedule of its own, and where a star spends little of its cycle at an extreme — the floor of an eclipse, most obviously — the sampling can miss it altogether. The classification and the period are the General Catalogue of Variable Stars’s. These elements as data.

[

DOUBLE STAR

] 11 PAIRS

COMPONENTS	SEPARATION	POSITION ANGLE	MAGNITUDE	MEASURED
Aa,Ab	0.1″	273°	—	1983
Aa,Ac	0.5″	278°	14.5	1983
AB	37.5″	113°	14.5	2023
AC	65″	289°	14.2	2023
AD	71.7″	345°	13.5	2023
AG	149.2″	47°	12.8	2023
AF	169.1″	266°	12.1	2023
AE	176.5″	155°	11	2023
AJ	191″	258°	13.5	2023
AI	217.8″	237°	13.5	2014
AH	240.2″	294°	11.2	2023

Separation and position angle are as measured in the year given; a position angle is measured from north, through east. Washington Double Star Catalog 05552+0724.

[

SPECTRUM

] A SPECTRUM OF ITS TYPE

TYPE SPECTRUM · M2 I

No survey in this catalogue has measured Betelgeuse’s own spectrum: the one that reaches deepest saturates on the brightest stars, and no spectrograph has been pointed at the whole sky. What is drawn below is the average of several real stars of the same class, M2 I — the nearest class the atlas holds to M1-M2Ia-Iab. It shows what a star like this one shows, and every line named on it is a line of the type rather than a measurement of Betelgeuse.

A star gives out light at every wavelength at once. The dark gaps are atoms in the thin gas above its surface, each one removing the single colour it is able to absorb — which is how a list of ingredients is read off something nobody will ever touch.

MADE OF

Point at a labelled line — or an element above — to see which atom makes it and where it falls.

HEAVY ELEMENTS The catalogued iron figure for Betelgeuse is +0.03, which puts it at about the Sun's share of the elements heavier than helium. The figure is a logarithm: nought is the Sun, and every whole step is a factor of ten. It comes from published measurements of the star itself, not from the spectrum above — which belongs to the type.

Pickles (1998) stellar spectral flux library. M2 I — the average of several real stars of this type, not an observation of any one star. Sampled every 5 angstroms; 1,895 points rebinned onto 1,024 log-spaced display points and normalised to the median flux. Brightness is scaled to this spectrum’s own middle value, so the shape is the measurement and the height is not. The 5 lines named above are the ones that stand clear of the scatter and of the features around them; a spectrum at this sampling holds many more that it cannot separate. The samples themselves, as JSON, CSV or VOTable.

[

LIFE OF THIS STAR

] STAGE 3 OF 5

Betelgeuse is a red supergiant near the end of its life; some time between the next few centuries and the next million years it will collapse and explode as a supernova, leaving a neutron star.

COLLAPSING CLOUD
took about forty thousand years
MAIN SEQUENCE
lasted about nine million years
SUPERGIANT
centuries to a million years left
NOW
SUPERNOVA
bright for weeks, over in a second
NEUTRON STAR
for the rest of time

NOW The same swelling, on a star heavy enough to keep going: helium, then carbon, then a run of heavier elements each burning faster than the last, until the core is iron and fusion can release nothing more.

NEXT The iron core collapses in about a second and the rest of the star is thrown off at a tenth of the speed of light. For a few weeks it outshines the galaxy it is in.

EVERY STAGE ON THIS TRACK

COLLAPSING CLOUDtook about forty thousand years: A cold clump of gas and dust falls in on itself and heats as it falls. It stops being a cloud and starts being a star at the moment its core is hot enough to fuse hydrogen.
MAIN SEQUENCElasted about nine million years: Hydrogen fuses to helium in the core, and the outward push of that exactly balances the star's own weight. This is the long, steady stretch — nine-tenths of a star's life — and it ends when the core's hydrogen is gone.
SUPERGIANTcenturies to a million years leftNOW: The same swelling, on a star heavy enough to keep going: helium, then carbon, then a run of heavier elements each burning faster than the last, until the core is iron and fusion can release nothing more.
SUPERNOVAbright for weeks, over in a second: The iron core collapses in about a second and the rest of the star is thrown off at a tenth of the speed of light. For a few weeks it outshines the galaxy it is in.
NEUTRON STARfor the rest of time: What is left of the core: a couple of solar masses in a ball the width of a city, so dense that its protons and electrons have been pressed into neutrons.

HOW FIRM How long a red supergiant has left depends on which fuel its core is burning, and that cannot be seen from outside — it is read from the star's pulsation, by working out which of its periods is the whole star ringing rather than its surface churning. The reading is disputed for every one of these stars, including the most-watched of them: one way round the core is still on helium and there are of the order of a hundred thousand years to go, the other way round it is already on carbon and there are centuries. That is why the figure above is a span. Nothing measured so far closes it.
ALSO No mass has been measured for this star, and past the main sequence its temperature no longer implies one — a red giant of one solar mass and a red supergiant of fifteen are the same colour. The figure above comes from its total output instead, and is unlikely to be better than a factor of two.

Which stage Betelgeuse is in was read from its catalogued class, its temperature and its total output at every wavelength — not from its brightness in visible light alone, which understates a cool star by a factor of several. The mass it started with is about twenty times the Sun's mass, from its luminosity, and that mass is what chooses the track. Every span of time here comes from the standard relation between a star’s mass and how long its fuel lasts, rounded to a single figure — except the stage this star is in, which that relation cannot reach, and which is given as the range the published readings actually cover. They are orders of magnitude and none of them is a date.

[

CATALOG DATA

] 22 FIELDS

The raw catalogue values, as the source published them, with the error bars where one was published — sorted by what each set of figures is about rather than by the order they happened to be stored in.

WHAT KIND OF THING IT IS

What the object is in itself, rather than how it happens to look from here.

Spectral type
Surface temperature: 3540
Luminosity: 13 415.3
Surface gravity (log g)
Metallicity ([Fe/H]): ±0.025
Variability: Semiregular pulsating supergiant
Variability type (): SRC
Variability period: 6.393

HOW BRIGHT IT IS

What the light adds up to, measured through one filter at a time. A magnitude is a brightness on a backwards scale — the smaller the number, the brighter the object.

Colour index (B−V)
Variable magnitude, brightest
Variable magnitude, faintest

WHERE IT IS AND HOW IT MOVES

Position, motion across the sky and the size it covers on it. These are measurements of the object as seen from here, so every one of them depends on where here is.

Proper motion (RA): 27.33
Proper motion (Dec): 10.86
: 21

OTHER NAMES AND NUMBERS

The identifiers other catalogues file this object under, for anyone joining this data to theirs.

Also known as: Alpha Orionis, alf Ori, α Ori, α Orionis
Variable-star designation: Alp Ori
Washington Double Star id: 05552+0724
Wikidata item: Q12124
Wikipedia article: Betelgeuse

WHERE THESE FIGURES CAME FROM

Which catalogue, paper or model each of the fields above was read from, where the source named one.

Spectral type from: SIMBAD (1989ApJS...71..245K, quality B)
Stellar parameters from: Spectroscopic determinations compiled from the literature (PASTEL, Soubiran+ 2016)
Metallicity from: Median of 2 spectroscopic determinations in 3 papers, compiled from the literature (PASTEL, Soubiran+ 2016); the error bar is the scatter between them

[

ALSO KNOWN AS

] 6 DESIGNATIONS

Bayer/Flamsteed 58 α Ori
Common name Betelgeuse
HD HD 39801
HIP HIP 27989
HR HR 2061
IRAS IRAS 05524+0723

[

LOOK IT UP ELSEWHERE

] 3 SERVICES

Each link carries the identifier printed beside it. Nothing on this page is a measurement of our own, so a number that disagrees with one of these is worth reporting — and a service that has never catalogued this object under this name will say so plainly.

SIMBADHR 2061
Cross-identifications, measured values and the reference behind each of them.
ADSobject:"HR 2061"
Papers indexed against this object rather than against the string, newest first.
VizieR5″ around 88.7929 +7.4071
Every published table with a row at this position, searched by coordinates rather than by name.

[

CITE THIS PAGE

] DR1

This page is live and its numbers move when an upstream refreshes, so the citation names the release the rows belong to rather than the day you read them. The release itself is frozen, republished as a bundle, and is what a data-availability statement should point at.

PLAIN TEXT

SpaceCatalog. Betelgeuse [catalogue entry]. Data release DR1 (2026-08-21). https://spacecatalog.org/object/betelgeuse

BIBTEX

@misc{spacecatalog_betelgeuse,
  author       = {{SpaceCatalog}},
  title        = {{Betelgeuse}},
  howpublished = {SpaceCatalog, data release DR1 (2026-08-21)},
  year         = {2026},
  url          = {https://spacecatalog.org/object/betelgeuse},
  note         = {Catalogue entry, data release DR1 (2026-08-21). Values from HYG Database v4.1.}
}

The values above were taken from HYG Database v4.1 — CC-BY-SA-4.0. Citing this page does not replace citing that catalogue, and its licence is share-alike: the terms reach whatever you build from these rows.

[