UY Cen
ILLUSTRATION FROM MEASURED TEMPERATURE · 2290 K · 714 L☉ · VARIABLE, MAG 6.60–7.17 · PERIOD 178.4 DAYS · PULSE COMPRESSED
OVERVIEW
] STARUY Cen is an S6/8 red star in the constellation Centaurus, 2189 from Earth, shining at apparent magnitude 6.85 (). It is catalogued as HD 115236 and HIP 64778.
- WHAT IT IS
- Red star
- HOW FAR
- 2189
- HOW BRIGHT (V)
The light arriving now left it that long ago.
Binoculars reach it; the naked eye does not.
OBSERVING
] FROM WHERE YOU AREWhat it takes to see UY Cen 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.
Say where you are, and this line says when UY Cen is worth going out for.
THROUGH AN EYEPIECE
] 150 MM TELESCOPE · 25 MM EYEPIECEToo faint for your eyes alone. Binoculars reach it. It will be a point of light in anything: a star is far enough away that no aperture on Earth gives it a width, and all the equipment changes is how easily you find it.
- 48×
- 1.08
- 1.25
- 13.0
- APPARENT MAGNITUDE ()
- 6.85 · within reach
APPARENT PLACE
] EQUINOX J2026.7Where 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
- 18.7
- PROPER MOTION SINCE
- 0.49
Computed for 2026-08-28 00:00 UT. Two things separate it from the catalogued position above: UY Cen 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 GIANT (POORLY DEFINED PERIODICITY)- RANGE, AS SAMPLED
- 6.60 – 7.17
- PERIOD
- 178.4 days
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.
LIFE OF THIS STAR
] STAGE 3 OF 5UY Cen is a red giant 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 CLOUDtook about ninety thousand years
- MAIN SEQUENCElasted about twenty million years
- GIANTcenturies to a million years leftNOW
- SUPERNOVAbright for weeks, over in a second
- NEUTRON STARfor 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 ninety 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 twenty 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.
- GIANTcenturies 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.
- ALSO Its class is one only an evolved star can have: the carbon on its surface was made in its own interior and dredged up, which is a thing that happens on the asymptotic giant branch and nowhere earlier.
Which stage UY Cen 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 ten 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
] 18 FIELDSThe 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
- 2291
- Luminosity
- 713.839
- Surface gravity (log g)
- Metallicity ([Fe/H])
- Variability
- Semiregular pulsating giant (poorly defined periodicity)
- Variability type ()
- SRB
- Variability period
- 178.4
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)
- −18.41
- Proper motion (Dec)
- 2
- Radial velocity
- −20.4
OTHER NAMES AND NUMBERS
The identifiers other catalogues file this object under, for anyone joining this data to theirs.
- Variable-star designation
- UY Cen
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 (1980ApJS...43..379K, quality B)
- Stellar parameters from
- Spectroscopic determinations compiled from the literature (PASTEL, Soubiran+ 2016)
- Metallicity from
- One spectroscopic determination, compiled from the literature (PASTEL, Soubiran+ 2016)
ALSO KNOWN AS
] 3 DESIGNATIONS- HD HD 115236
- HIP HIP 64778
- Variable star UY Cen
LOOK IT UP ELSEWHERE
] 3 SERVICESEach 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.
- SIMBADHD 115236
Cross-identifications, measured values and the reference behind each of them.
- ADSobject:"HD 115236"
Papers indexed against this object rather than against the string, newest first.
- VizieR5″ around 199.1327 -44.7044
Every published table with a row at this position, searched by coordinates rather than by name.
CITE THIS PAGE
] DR1This 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.
SpaceCatalog. UY Cen [catalogue entry]. Data release DR1 (2026-08-21). https://spacecatalog.org/object/hd-115236
@misc{spacecatalog_hd-115236,
author = {{SpaceCatalog}},
title = {{UY Cen}},
howpublished = {SpaceCatalog, data release DR1 (2026-08-21)},
year = {2026},
url = {https://spacecatalog.org/object/hd-115236},
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.