RT CrB
ILLUSTRATION FROM SPECTRAL TYPE G0 · 5940 K · VARIABLE, MAG 10.13–10.57 · PERIOD 5.117 DAYS · PULSE COMPRESSED
OVERVIEW
] STARRT CrB is a G0 yellow star in the constellation Corona Borealis, shining at apparent magnitude 10.21 (). It is catalogued as HD 139588 and HIP 76551.
- WHAT IT IS
- Yellow star
- HOW BRIGHT (V)
A small telescope reaches it.
OBSERVING
] FROM WHERE YOU AREWhat it takes to see RT CrB 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 RT CrB 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 0.20″ away, which at 48× is blended into one star.
- 48×
- 1.08
- 1.25
- 13.0
- 0.20 · blended into one star
- APPARENT MAGNITUDE ()
- 10.21 · within reach
A is where the pair was the year it was measured — the ones above, in 2018, and a pair in a real orbit has moved since.
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
- 15.4
- PROPER MOTION SINCE
- 0.19
Computed for 2026-08-27 00:00 UT. Two things separate it from the catalogued position above: RT CrB 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
] ALGOL-TYPE ECLIPSING BINARY- RANGE, AS SAMPLED
- 10.13 – 10.57
- PERIOD
- 5.117159 days
- PHASE
- 0.113 ± 0.0006
- NEXT MINIMUM
- 2026-08-31 12:53 UT---------- --:-- your time
Computed for 2026-08-27 00:00 UT. A phase of zero is minimum light, and RT CrB was last there 13.9 h before that. The ± is what the published elements can still promise: 6,450 cycles have gone by since the epoch they were measured at, and the last digit of the period compounds over every one of them — 4.7 min 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 |
|---|---|---|---|---|
| — | 0.2″ | -1° | — | 2018 |
Separation and position angle are as measured in the year given; a position angle is measured from north, through east. Washington Double Star Catalog 15381+2929.
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 IT IS MADE OF
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/AR:/RS
- Variability period
- 5.117159
- 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)
- 6.81
- Proper motion (Dec)
- −1.46
- Radial velocity
- −4
OTHER NAMES AND NUMBERS
The identifiers other catalogues file this object under, for anyone joining this data to theirs.
- Variable-star designation
- RT CrB
- Washington Double Star id
- 15381+2929
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 (1993yCat.3135....0C, quality E)
ALSO KNOWN AS
] 3 DESIGNATIONS- HD HD 139588
- HIP HIP 76551
- Variable star RT CrB
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 139588
Cross-identifications, measured values and the reference behind each of them.
- ADSobject:"HD 139588"
Papers indexed against this object rather than against the string, newest first.
- VizieR5″ around 234.5126 +29.4872
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. RT CrB [catalogue entry]. Data release DR1 (2026-08-21). https://spacecatalog.org/object/hd-139588
@misc{spacecatalog_hd-139588,
author = {{SpaceCatalog}},
title = {{RT CrB}},
howpublished = {SpaceCatalog, data release DR1 (2026-08-21)},
year = {2026},
url = {https://spacecatalog.org/object/hd-139588},
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.