RU Aur
ILLUSTRATION FROM SPECTRAL TYPE M9e · 2500 K · VARIABLE, MAG 10.99–14.63 · PERIOD 463 DAYS · PULSE COMPRESSED
OBSERVING
] FROM WHERE YOU AREWhat it takes to see RU Aur 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 RU Aur is worth going out for.
THROUGH AN EYEPIECE
] 150 MM TELESCOPE · 25 MM EYEPIECEOut of reach of binoculars; a 150 mm telescope reaches 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 ()
- 11.91 · 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
- 21.8
- PROPER MOTION SINCE
- 1.75
Computed for 2026-08-27 00:00 UT. Two things separate it from the catalogued position above: RU Aur 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
] MIRA LONG-PERIOD VARIABLE- RANGE, AS SAMPLED
- 10.99 – 14.63
- PERIOD
- 463 days (463 days)
- PHASE
- 0.033 ± 0.015
- NEXT MAXIMUM
- 2027-11-17 11:53 UT---------- --:-- your time
Computed for 2026-08-27 00:00 UT. A phase of zero is maximum light, and RU Aur was last there 15.5 days before that. The ± is what the published elements can still promise: 14 cycles have gone by since the epoch they were measured at, and the last digit of the period compounds over every one of them — 7.03 days 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. For this kind of star the period is a mean over cycles that individually run long or short, so the time above is an expectation and not an appointment. 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.
SPECTRUM
] A SPECTRUM OF ITS TYPENo survey in this catalogue has measured RU Aur’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, M6 V — the nearest class the atlas holds to M9e. 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 RU Aur.
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. M6 V — the average of several real stars of this type, not an observation of any one star. Sampled every 5 angstroms; 1,895 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 2 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 3RU Aur is a red dwarf on the main sequence, and it will stay there for trillions of years — many times longer than the universe has so far existed — before fading to a white dwarf without ever becoming a giant.
- COLLAPSING CLOUDtook about five hundred million years
- MAIN SEQUENCEabout four trillion years in allNOW
- WHITE DWARFlong after the universe as it is now
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 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.
EVERY STAGE ON THIS TRACK
- COLLAPSING CLOUDtook about five 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 four trillion 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.
- WHITE DWARFlong after the universe as it is now
- 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 RU Aur 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 a tenth of 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
] 13 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
- Mira long-period variable
- Variability type ()
- M
- Variability period
- 463
- 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)
- 63.32
- Proper motion (Dec)
- −16.75
- Radial velocity
- 0
OTHER NAMES AND NUMBERS
The identifiers other catalogues file this object under, for anyone joining this data to theirs.
- Variable-star designation
- RU Aur
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 (2019MNRAS.485.2167G, quality D)
ALSO KNOWN AS
] 2 DESIGNATIONS- HIP HIP 26675
- Variable star RU Aur
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 26675
Cross-identifications, measured values and the reference behind each of them.
- ADSobject:"HIP 26675"
Papers indexed against this object rather than against the string, newest first.
- VizieR5″ around 85.0330 +37.6363
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. RU Aur [catalogue entry]. Data release DR1 (2026-08-21). https://spacecatalog.org/object/hip-26675
@misc{spacecatalog_hip-26675,
author = {{SpaceCatalog}},
title = {{RU Aur}},
howpublished = {SpaceCatalog, data release DR1 (2026-08-21)},
year = {2026},
url = {https://spacecatalog.org/object/hip-26675},
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.