HIP 54639
ILLUSTRATION FROM MEASURED TEMPERATURE · 5310 K · 0.0984 L☉ · VARIABLE, MAG 11.31–11.47 · TIMING NOT TO SCALE
OVERVIEW
] STARHIP 54639 is an in the constellation Leo, 207.9 from Earth, shining at apparent magnitude 11.39 ().
- WHAT IT IS
- Yellow subdwarf
- HOW FAR
- 207.9
- HOW BRIGHT (V)
The light arriving now left it that long ago.
A small telescope reaches it.
THE MODEL
] CATALOGUED RADIUSCALCULATED · NOT AN OBSERVATION · CATALOGUED RADIUS · MEASURED TEMPERATURE · 5310 K · 0.0984 L☉ · VARIABLE, MAG 11.31–11.47
Drawn from the catalogued radius and from the same properties the picture at the top of this page uses, at the distance a flight to it would stop. 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.
OBSERVING
] FROM WHERE YOU AREWhat it takes to see HIP 54639 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 HIP 54639 is worth going out for.
THROUGH AN EYEPIECE
] 150 MM TELESCOPE · 25 MM EYEPIECEOut of reach of binoculars; a 150 mm telescope reaches it. Its brightest companion sits 16.1″ away, which at 48× is cleanly split.
- 48×
- 1.08
- 1.25
- 13.0
- 16.1 · cleanly split
- APPARENT MAGNITUDE ()
- 11.39 · within reach
A is where the pair was the year it was measured — the ones above, in 2015, and a pair in a real orbit has moved since. The brightest companion is 8.3 magnitudes down on the star itself, which makes it a harder split than the angle alone suggests: the glare of the brighter one is what you are separating it from.
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
- 22.5
- PROPER MOTION SINCE
- 20.3
Computed for 2026-08-27 00:00 UT. Two things separate it from the catalogued position above: HIP 54639 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.
DOUBLE STAR
] 1 PAIR| COMPONENTS | SEPARATION | POSITION ANGLE | MAGNITUDE | MEASURED |
|---|---|---|---|---|
| — | 16.1″ | 112° | 19.7 | 2015 |
Separation and position angle are as measured in the year given; a position angle is measured from north, through east. Washington Double Star Catalog 11110+0625.
LIFE OF THIS STAR
] STAGE 2 OF 5HIP 54639 is a yellow star on the main sequence, fusing hydrogen in its core — about thirty billion years of it in all — and when that hydrogen is gone it will swell into a red giant, and end as a white dwarf.
- COLLAPSING CLOUDtook about a hundred million years
- MAIN SEQUENCEabout thirty billion years in allNOW
- RED GIANTabout three billion years of it, when it comes
- PLANETARY NEBULAgone in about twenty thousand years
- WHITE DWARFcooling from then on
NOW 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.
NEXT With the core out of hydrogen, the star swells enormously and its surface cools to red. It burns helium in the core and hydrogen in a shell around it, and it loses mass from its surface the whole time.
EVERY STAGE ON THIS TRACK
- COLLAPSING CLOUDtook about a hundred million 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 SEQUENCEabout thirty billion years in allNOW
- 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.
- RED GIANTabout three billion years of it, when it comes
- With the core out of hydrogen, the star swells enormously and its surface cools to red. It burns helium in the core and hydrogen in a shell around it, and it loses mass from its surface the whole time.
- PLANETARY NEBULAgone in about twenty thousand years
- The outer layers drift away and the exposed core lights them from inside. It is one of the shortest things a star does and one of the most visible — most of the glowing shells in this catalogue are this stage of some star.
- WHITE DWARFcooling from then on
- The bare core, about the size of the Earth, held up by nothing but the resistance of its own crushed electrons. No fusion, no fuel, nothing left to do but cool.
- HOW FIRM No luminosity class is recorded for this star — the catalogue gives its temperature class and stops there — so which stage it is in was read from how far its brightness sits above where a star of its temperature would sit on the main sequence. That is a best estimate rather than a classification.
- ALSO No mass has been measured for this star. The figure above is inferred from its temperature by way of the main-sequence relation between the two, which is tight enough to be worth stating and is still an inference.
Which stage HIP 54639 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 half 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, and is rounded to a single figure: they are orders of magnitude and none of them is a date.
CATALOG DATA
] 15 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
- 5306
- Luminosity
- 0.0983558
- Luminosity (bolometric)
- 0.217
- Radius
- 0.552
- Surface gravity (log g)
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)
- −565.13
- Proper motion (Dec)
- −509.99
- Radial velocity
- 0
OTHER NAMES AND NUMBERS
The identifiers other catalogues file this object under, for anyone joining this data to theirs.
- Washington Double Star id
- 11110+0625
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 (1998ApJ...500..398R, quality D)
- Stellar parameters from
- Gaia DR3 model fit (GSP-Phot, FLAME; RUWE ≤ 1.4)
ALSO KNOWN AS
] 1 DESIGNATIONS- HIP HIP 54639
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.
- SIMBADHIP 54639
Cross-identifications, measured values and the reference behind each of them.
- ADSobject:"HIP 54639"
Papers indexed against this object rather than against the string, newest first.
- VizieR5″ around 167.7500 +6.4199
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. HIP 54639 [catalogue entry]. Data release DR1 (2026-08-21). https://spacecatalog.org/object/hip-54639
@misc{spacecatalog_hip-54639,
author = {{SpaceCatalog}},
title = {{HIP 54639}},
howpublished = {SpaceCatalog, data release DR1 (2026-08-21)},
year = {2026},
url = {https://spacecatalog.org/object/hip-54639},
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.