Bellatrix is the third-brightest star in the constellation of Orion, positioned 5° west of the red supergiant Betelgeuse. It has the Bayer designation γ Orionis, which is Latinized to Gamma Orionis. With a slightly variable magnitude of around 1.6, it is typically the 25th-brightest star in the night sky. Located at a distance of 250±10 light-years from the Sun, it is a blue giant star around 7.7 times as massive as the sun with 5.75 times its diameter.
In stellar evolution, an FU Orionis star is a pre–main-sequence star which displays an extreme change in magnitude and spectral type. One example is the star V1057 Cyg, which became 6 magnitudes brighter and went from spectral type dKe to F-type supergiant during 1969-1970. These stars are named after their type-star, FU Orionis.
Iota Orionis is a multiple star system in the equatorial constellation of Orion the hunter. It is the eighth-brightest member of Orion with an apparent visual magnitude of 2.77 and also the brightest member of the asterism known as Orion's Sword. It is a member of the NGC 1980 open cluster. From parallax measurements, it is located at a distance of roughly 1,340 light-years from the Sun.
Upsilon Orionis is a star in the constellation Orion. It has the traditional name Thabit or Tabit, a name shared with pi3 Orionis. It is a blue-white main sequence star of apparent magnitude 4.62 located over 3000 light-years distant from the Solar System. It is a suspected Beta Cephei variable.
Sigma Orionis or Sigma Ori is a multiple star system in the constellation Orion, consisting of the brightest members of a young open cluster. It is found at the eastern end of the belt, south west of Alnitak and west of the Horsehead Nebula which it partially illuminates. The combined brightness of the component stars is magnitude 3.80.
S Persei is a red supergiant or hypergiant located near the Double Cluster in Perseus, north of the cluster NGC 869. It is a member of the Perseus OB1 association and one of the largest known stars. If placed in the Solar System, its photosphere would engulf the orbit of Jupiter. It is also a semiregular variable, a star whose variations are less regular than those of Mira variables.
V1057 Cygni is a suspected binary star system in the northern constellation of Cygnus. It is a variable star of the FU Orionis-type, and was the second FU Orionis-type variable to be discovered. The system is located at a distance of approximately 3,000 light years from the Sun, in the North America Nebula. It has an apparent visual magnitude of around 12.4.
U Orionis is a Mira-type variable star in the constellation Orion. It is a classical long period variable star that has been well observed for over 120 years.
RU Lupi is a star in the constellation of Lupus, located in the young Lupus Star Forming Region. Based on parallax measurements, the distance to this star is about 514 light-years (158 pc). The apparent visual magnitude is 10.5, so viewing it would require a telescope with an aperture of 6 cm (2 in), but preferably larger.
25 Orionis, less commonly known by its Bayer designation Psi1 Orionis is a fifth-magnitude star in the constellation Orion. It lies among a dense cluster of low-mass pre-main-sequence stars in the Orion OB1a.
Theta1 Orionis A is a variable trinary star in the constellation Orion. Its apparent magnitude range is 6.72 to 7.65 with a period of 65.432 days. It is one of the main stars in The Trapezium in Orion, along with B, C, and D, as well as the fainter E.
Theta2 Orionis is a multiple star system in the constellation Orion. It is a few arc minutes from its more famous neighbour the Trapezium Cluster, also known as θ1 Orionis.
BC Cygni is a red supergiant and pulsating variable star of spectral type M3.5Ia in the constellation Cygnus.
Theta1 Orionis B, also known as BM Orionis, is a multiple star system containing at least five members. It is also one of the main stars of the Trapezium Cluster, with the others being A, C, and D. The primary is an eclipsing variable and one of the youngest known eclipsing binary systems.
RY Tauri is a young T Tauri star in the constellation of Taurus about 450 light years away, belonging to the Taurus Molecular Cloud. It is more massive than typical T Tauri stars, and may be an intermediate between this class and the Herbig Ae/Be star type.
BF Orionis is a young Herbig Ae/Be star in the constellation of Orion about 1250 light years away, within the Orion Nebula. It is the most massive star of the small birth cluster of four stars.
EX Lupi is a young, single T-Tauri star in the southern constellation of Lupus. An irregular variable, it is the prototype of young, low-mass eruptive stars named EXors, with EX Lupi being this object's variable star designation. At its minimal activity level, EX Lupi resembles a classical T-Tauri star of the M0 dwarf type. The low latitude of this star, at a declination of −40°, makes it difficult for northern observers to view. Based on parallax measurements, it is located at a distance of about 505 light years from the Sun. The star lies next to a gap in the Lupus cloud complex, a star forming region.
CQ Tauri is a young variable star in the equatorial constellation of Taurus. It is too faint to be visible to the naked eye with an apparent visual magnitude that ranges from 8.7 to 12.25. The distance to this star is approximately 487 light years based on parallax measurements, and it is drifting further away with a radial velocity of ~23 km/s. It appears to be part of the T-association Tau 4. CQ Tauri lies close enough to the ecliptic to undergo lunar occultations.
UX Orionis is a variable star in the constellation of Orion. It is a Herbig Ae star, located about 1000 light years from the Earth. At its brightest it is a magnitude 9.5 object, so it is too faint to be seen with the naked eye. UX Orionis is the prototype of the UX Orionis class of variable stars, which are young stellar objects that exhibit large, irregular changes in visual band brightness. UX Orionis was discovered by Henrietta Swan Leavitt.
