An Orion variable is a variable star which exhibits irregular and eruptive variations in its luminosity and is typically associated with diffuse nebulae. It is thought that these are young stars which will later become regular, non-variable stars on the zero-age main sequence. Brightness fluctuations can be as much as several magnitudes.

T Tauri stars are Orion variables exhibiting characteristic fluorescent violet emission lines from singly ionized iron (Fe II) in their star spectra, and also emission from lithium, a metal that usually is destroyed by the nuclear fusion in the stars.

FU Orionis stars or simply "Fuors", are Orion variables that rise 5–6 magnitudes, then sink up to one magnitude and stay there for many decades. The prototype is FU Orionis, and other specimens are V1057 Cygni and V1515 Cygni.

Of this diverse class of stars, some Orion variables may exhibit a small amplitude (up to 1 magnitude) periodic variation, some are characterized by abrupt fadings, and some show spectral characteristics indicating mass downfall upon the star (YY Orionis stars). Many of these characteristics may occur in any one Orion variable.

The term 'Orion Variable' was a handy catch-all term but is now tending to drop out of disuse among the astronomical community, though for historical reasons the GCVS still uses it. Astronomers use more specialised terms which refer to actual physical differences among the 'zoo' of young variable stars, such as 'Classical T Tauri' or 'UX Orionis' stars.

• Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1: B/gcvs. Bibcode:2009yCat....102025S.
• Glasby, John Stephen (1974). The nebular variables. Bibcode:1974neva.book.....G.
• Cohen, M.; Dewhirst, D. W. (1973). "Infra-Red Observations of Young Stars-II: T TAURI STARS AND THE ORION POPULATION". Monthly Notices of the Royal Astronomical Society. 161: 97–104. Bibcode:1973MNRAS.161...97C. doi:10.1093/mnras/161.1.97.

• GCVS Variability Types

v t e Variable stars
Pulsating	Cepheids and cepheid-like Type I (Classical cepheids, Delta Scuti) Type II (BL Herculis, W Virginis, RV Tauri) RR Lyrae Rapidly oscillating Ap SX Phoenicis Blue-white with early spectra Alpha Cygni Beta Cephei Slowly pulsating B-type PV Telescopii Blue large-amplitude pulsator Long-period Mira Semiregular Slow irregular Other Gamma Doradus Solar-like oscillations White dwarf
Eruptive	Protostar and PMS Herbig Ae/Be Orion FU Orionis T Tauri Giants and supergiants Luminous blue variable R Coronae Borealis (DY Persei) Yellow hypergiant Eruptive binary Double periodic FS Canis Majoris RS Canum Venaticorum Other Flare Gamma Cassiopeiae Lambda Eridani Wolf–Rayet
Cataclysmic	AM Canum Venaticorum Dwarf nova Luminous red nova Nova Polar Intermediate Supernova Hypernova SW Sextantis Symbiotic Symbiotic nova Z Andromedae
Rotating	Non-spherical Rotating ellipsoidal Stellar spots BY Draconis FK Comae Berenices Magnetic fields α2 Canum Venaticorum Pulsar SX Arietis
Eclipsing	Algol Beta Lyrae Planetary transit W Ursae Majoris
Star portal * List