HD 201345
ILLUSTRATION FROM SPECTRAL TYPE ON9.2IV · 40 000 K · 556 L☉
OVERVIEW
] STARHD 201345 is an ON9.2IV blue star in the constellation Cygnus, 2965 from Earth, shining at apparent magnitude 7.78 (). It is catalogued as HIP 104316.
- WHAT IT IS
- Blue star
- HOW FAR
- 2965
- HOW BRIGHT (V)
The light arriving now left it that long ago.
Binoculars reach it; the naked eye does not.
THE MODEL
] RADIUS FROM THE LUMINOSITY AND THE TEMPERATURECALCULATED · NOT AN OBSERVATION · RADIUS FROM THE LUMINOSITY AND THE TEMPERATURE · SPECTRAL TYPE ON9.2IV · 40 000 K · 556 L☉
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. 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, drawn from where the camera actually is — but every one of them is within 170 parsecs of the Sun and this object is much further out, so what is in the frame is that whole neighbourhood seen from outside it, piled into a knot around the Sun. The rest of the sky from here is not something this catalogue knows.
OBSERVING
] FROM WHERE YOU AREWhat it takes to see HD 201345 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 HD 201345 is worth going out for.
THROUGH AN EYEPIECE
] 150 MM TELESCOPE · 25 MM EYEPIECEToo faint for your eyes alone. Binoculars reach it. Its brightest companion sits 6.10″ away, which at 48× is cleanly split.
- 48×
- 1.08
- 1.25
- 13.0
- 6.10 · cleanly split
- APPARENT MAGNITUDE ()
- 7.78 · within reach
A is where the pair was the year it was measured — the ones above, in 2012, and a pair in a real orbit has moved since. The brightest companion is 9.2 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
- 15.2
- PROPER MOTION SINCE
- 0.21
Computed for 2026-08-27 00:00 UT. Two things separate it from the catalogued position above: HD 201345 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 |
|---|---|---|---|---|
| — | 6.1″ | 221° | 17 | 2012 |
Separation and position angle are as measured in the year given; a position angle is measured from north, through east. Washington Double Star Catalog 21079+3324.
SPECTRUM
] A SPECTRUM OF ITS TYPENo survey in this catalogue has measured HD 201345’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, B2 IV — the nearest class the atlas holds to ON9.2IV. 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 HD 201345.
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.
Point at a labelled line — or an element above — to see which atom makes it and where it falls.
Pickles (1998) stellar spectral flux library. B2 IV — the average of several real stars of this type, not an observation of any one star. Sampled every 5 angstroms; 1,894 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 2 OF 5HD 201345 is a subgiant: it has used up the hydrogen in its core, it has begun to swell and cool, and it is on its way off the main sequence. In about a hundred thousand years it will swell into a supergiant, and end by exploding as a supernova and leaving a black hole.
- COLLAPSING CLOUDtook about five thousand years
- MAIN SEQUENCEat the end of itNOW
- SUPERGIANTabout a hundred thousand years of it, when it comes
- SUPERNOVAbright for weeks, over in a second
- BLACK HOLEfor the rest of time
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. This star is at the very end of that: its spectrum is classed as a subgiant, which is what a star is called in the short crossing between running out of core hydrogen and swelling into a giant.
NEXT 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.
EVERY STAGE ON THIS TRACK
- COLLAPSING CLOUDtook about five 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 SEQUENCEat the end of itNOW
- 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.
- SUPERGIANTabout a hundred thousand years of it, when it comes
- 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.
- BLACK HOLEfor the rest of time
- Nothing the core could be made of is stiff enough to stop the collapse, so it does not stop. What remains is a region of space that light cannot leave.
- HOW FIRM 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.
- ALSO A subgiant is the hardest kind of star to place. It is between two stages rather than in one of them, it is the shortest stretch of a star's life, and the mass it started with is what decides how long the crossing takes — so the timing above is the least firm figure in this section.
Which stage HD 201345 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 forty times the Sun's mass, from its temperature, 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
] 8 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
- Luminosity
- 556.16
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)
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)
- 1.78
- Proper motion (Dec)
- −7.69
- Radial velocity
- 19.2
OTHER NAMES AND NUMBERS
The identifiers other catalogues file this object under, for anyone joining this data to theirs.
- Washington Double Star id
- 21079+3324
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 (2014ApJS..211...10S, quality C)
ALSO KNOWN AS
] 2 DESIGNATIONS- HD HD 201345
- HIP HIP 104316
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 201345
Cross-identifications, measured values and the reference behind each of them.
- ADSobject:"HD 201345"
Papers indexed against this object rather than against the string, newest first.
- VizieR5″ around 316.9809 +33.3970
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. HD 201345 [catalogue entry]. Data release DR1 (2026-08-21). https://spacecatalog.org/object/hd-201345
@misc{spacecatalog_hd-201345,
author = {{SpaceCatalog}},
title = {{HD 201345}},
howpublished = {SpaceCatalog, data release DR1 (2026-08-21)},
year = {2026},
url = {https://spacecatalog.org/object/hd-201345},
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.