NGC 1990
ILLUSTRATION FROM MEASURED TEMPERATURE · 25 800 K
OVERVIEW
] STARNGC 1990 is a star in the constellation Orion, shining at apparent magnitude 1.69 (). Other catalogues list it as 46 Ori, BD -01 0969 and Alnilam, among 12 designations in total. It was discovered in 1786.
- WHAT IT IS
- Star
- HOW BRIGHT (V)
Bright enough for the naked eye, under a sky dark enough.
OBSERVING
] FROM WHERE YOU AREWhat it takes to see NGC 1990 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 NGC 1990 is worth going out for.
THROUGH AN EYEPIECE
] 150 MM TELESCOPE · 25 MM EYEPIECEBright enough to pick out with your eyes alone, and from a lit street as well as a dark one. 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 ()
- 1.69 · within reach
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
- 20.5
- PROPER MOTION SINCE
- none published
Computed for 2026-10-11 00:00 UT. No proper motion is published for NGC 1990, so nothing here moves the object; what separates this from the catalogued position above is the coordinate grid turning 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.
LIFE OF THIS STAR
] STAGE 2 OF 5NGC 1990 is a blue-white star on the main sequence, fusing hydrogen in its core — about six 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 thirty thousand years
- MAIN SEQUENCEabout six million years in allNOW
- SUPERGIANTabout six 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 thirty 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 six 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 six 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 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.
- 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 NGC 1990 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.
- Surface temperature
- 25 835
- 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.
- Apparent magnitude ()
- Apparent magnitude ()
- Apparent magnitude ()
- Apparent magnitude ( band)
- Apparent magnitude ()
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.
- 27
- Redshift (z)
WHEN IT WAS FOUND
Who first saw it, from where, and by what method.
- Discovered by
- William Herschel
OTHER NAMES AND NUMBERS
The identifiers other catalogues file this object under, for anyone joining this data to theirs.
- OpenNGC type code
- *
- Wikidata item
- Q1046370
- Wikipedia article
- NGC 1990
WHERE THESE FIGURES CAME FROM
Which catalogue, paper or model each of the fields above was read from, where the source named one.
- Stellar parameters from
- Spectroscopic determinations compiled from the literature (PASTEL, Soubiran+ 2016)
ALSO KNOWN AS
] 12 DESIGNATIONS- 46 46 Ori
- BD BD -01 0969
- Common name Alnilam
- Eps Eps Ori
- HD HD 37128
- HIP HIP 26311
- IDS IDS 05311-0116 A
- Lynds LBN 205.42-17.78
- Lynds LBN 940
- NGC NGC 1990
- TYC TYC 4766-2450-1
- WDS WDS J05362-0112A
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.
- SIMBADNGC 1990
Cross-identifications, measured values and the reference behind each of them.
- ADSobject:"NGC 1990"
Papers indexed against this object rather than against the string, newest first.
- VizieR5″ around 84.0534 -1.2019
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. NGC 1990 [catalogue entry]. Data release DR1 (2026-08-21). https://spacecatalog.org/object/ngc-1990
@misc{spacecatalog_ngc-1990,
author = {{SpaceCatalog}},
title = {{NGC 1990}},
howpublished = {SpaceCatalog, data release DR1 (2026-08-21)},
year = {2026},
url = {https://spacecatalog.org/object/ngc-1990},
note = {Catalogue entry, data release DR1 (2026-08-21). Values from OpenNGC.}
}The values above were taken from OpenNGC — 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: OpenNGC, Mattia Verga (github.com/mattiaverga/OpenNGC). Fields derived from it stay under CC BY-SA 4.0.