δ Cir
ILLUSTRATION FROM SPECTRAL TYPE O8V · 35 600 K · VARIABLE, MAG 5.02–5.17 · PERIOD 3.902 DAYS · PULSE COMPRESSED
OBSERVING
] FROM WHERE YOU AREWhat it takes to see δ Cir 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 δ Cir is worth going out for.
THROUGH AN EYEPIECE
] 150 MM TELESCOPE · 25 MM EYEPIECEBright enough to see with your eyes alone, once you are away from town lights. Its brightest companion sits 53.9″ away, which at 48× is cleanly split.
- 48×
- 1.08
- 1.25
- 13.0
- · AB
- 53.9 · cleanly split
- APPARENT MAGNITUDE ()
- 5.04 · within reach
A is where the pair was the year it was measured — the ones above, in 2016, and a pair in a real orbit has moved since. The brightest companion — AB — is 7.8 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.
APPARENT PLACE
] EQUINOX J2026.8Where 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
- 17.0
- PROPER MOTION SINCE
- 0.12
Computed for 2026-10-12 00:00 UT. Two things separate it from the catalogued position above: δ Cir 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. The catalogue it came from publishes no error for that position, so nothing here says how far this arithmetic can be trusted — the digits above are as precise as the place they were computed from, and no more. Aberration, parallax and refraction are left out. Aberration swings every position by up to twenty arcseconds over a year; parallax stays under an arcsecond for all but the nearest stars; refraction is nothing overhead and about half a degree at the horizon, where it answers to the air, not the sky. The same figure for any date.
VARIABILITY
] ALGOL-TYPE ECLIPSING BINARY- RANGE, AS SAMPLED
- 5.02 – 5.17
- PERIOD
- 3.9023 days
- PHASE
- 0.681 ± 0.042
- NEXT MINIMUM
- 2026-10-13 05:51 UT---------- --:-- your time
- THEN
- 2026-10-17 03:30 UT---------- --:-- your time
Computed for 2026-10-12 00:00 UT. A phase of zero is minimum light, and δ Cir was last there 2.66 days before that. The ± is what the published elements can still promise: 3,285 cycles have gone by since the epoch they were measured at, and the last digit of the period compounds over every one of them — 3.9 h by now. It is the precision of the published figures rather than an error bar the catalogue supplied, so where that catalogue has marked a period doubtful the real spread is wider — and it does not contain the star. A binary with a third body in the system, or a pulsator whose period is slowly changing, walks away from a straight-line ephemeris by an amount only observation settles. Times are corrected for where the Earth is in its orbit, which is worth up to 8.3 minutes — the light of a star reaches us that much earlier in one season than the other, and an epoch measured a century ago has the same correction in it.
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, the period and the epoch are the General Catalogue of Variable Stars’s. The phase at any instant.
DOUBLE STAR
] 1 PAIR| COMPONENTS | SEPARATION | POSITION ANGLE | MAGNITUDE | MEASURED |
|---|---|---|---|---|
| AB | 53.9″ | 279° | 12.87 | 2016 |
Separation and position angle are as measured in the year given; a position angle is measured from north, through east. Washington Double Star Catalog 15169-6057.
SPECTRUM
] A SPECTRUM OF ITS TYPENo survey in this catalogue has measured δ Cir’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, O9 V — the nearest class the atlas holds to O8V. 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 δ Cir.
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. O9 V — the average of several real stars of this type, not an observation of any one star. Sampled every 5 angstroms; 1,891 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 5δ Cir is a blue star on the main sequence, fusing hydrogen in its core — about five million years of it in all — and when that hydrogen is gone it will swell into a supergiant, and end by exploding as a supernova and leaving a neutron star — or a black hole, if enough of the core falls back.
- COLLAPSING CLOUDtook about twenty thousand years
- MAIN SEQUENCEabout five million years in allNOW
- SUPERGIANTabout five hundred thousand years of it, when it comes
- SUPERNOVAbright for weeks, over in a second
- NEUTRON STARfor 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.
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 twenty 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 SEQUENCEabout five million 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.
- SUPERGIANTabout five 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.
- 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 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 Whether a core this heavy leaves a neutron star or a black hole depends on how much of the star falls back onto it after the explosion, which is not something an observation before the event can answer.
Which stage δ Cir 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 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, rounded to a single figure. They are orders of magnitude and none of them is a date.
CATALOG DATA
] 14 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
- Variability
- Algol-type eclipsing binary
- Variability type ()
- EA
- Variability period
- 3.9023
- Reference epoch ()
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)
- −2.02
- Proper motion (Dec)
- −4.08
- 9
OTHER NAMES AND NUMBERS
The identifiers other catalogues file this object under, for anyone joining this data to theirs.
- Variable-star designation
- Del Cir
- Washington Double Star id
- 15169-6057
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
] 4 DESIGNATIONS- Bayer/Flamsteed δ Cir
- HD HD 135240
- HIP HIP 74778
- HR HR 5664
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.
- SIMBADHR 5664
Cross-identifications, measured values and the reference behind each of them.
- ADSobject:"HR 5664"
Papers indexed against this object rather than against the string, newest first.
- VizieR5″ around 229.2371 -60.9573
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. δ Cir [catalogue entry]. Data release DR1 (2026-08-21). https://spacecatalog.org/object/hd-135240
@misc{spacecatalog_hd-135240,
author = {{SpaceCatalog}},
title = {{δ Cir}},
howpublished = {SpaceCatalog, data release DR1 (2026-08-21)},
year = {2026},
url = {https://spacecatalog.org/object/hd-135240},
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.
That catalogue asks for this acknowledgement: HYG Database v4.1, Astronexus (github.com/astronexus/HYG-Database). Fields derived from it stay under CC BY-SA 4.0.