R Hydrae, abbreviated R Hya, is a single star in the equatorial constellation of Hydra, about 2.7° to the east of Gamma Hydrae. It is a Mira-type variable that ranges in apparent visual magnitude from 3.5 down to 10.9 over a period of 389 days. At maximum brightness the star can be seen with the naked eye, while at minimum a telescope of at least 5 cm is needed. This star is located at a distance of approximately 480 light-years from the Sun but is drifting closer with a radial velocity of −10 km/s.
Sigma Hydrae, also named Minchir, is a solitary star in the equatorial constellation of Hydra. It is visible to the naked eye with an apparent visual magnitude of 4.48. The estimated distance to this star from the Sun, based upon an annual parallax shift of 8.75 mas, is around 370 light-years. At that distance, the visual magnitude of the star is diminished by an interstellar extinction factor of 0.16, due to intervening dust.
R Horologii is a red giant star approximately 760 light-years away in the southern constellation of Horologium. It is a Mira variable with a period of 404.83 days, ranging from apparent magnitude 4.7 to 14.3—one of the largest ranges in brightness known of stars in the night sky visible to the unaided eye. The star is losing mass at the rate of 5.9×10−7 M☉·y−1.
Iota Centauri, Latinized from ι Centauri, is a star in the southern constellation of Centaurus. Based upon parallax measurements, it lies at a distance of approximately 58.6 light-years from Earth. Iota Centauri has an apparent visual magnitude of +2.73, making it easily visible to the naked eye.
AB Doradus is a pre-main-sequence quadruple star system in the constellation Dorado. The primary is a flare star that shows periodic increases in activity.
Delta Hydrae, Latinized from δ Hydrae, is a double star in the equatorial constellation of Hydra. It is visible to the naked eye with an apparent visual magnitude of 4.146. Based upon an annual parallax shift of 20.34 mas, it is located about 160 light years from the Sun.
Xi Hydrae, Latinised from ξ Hydrae, is a solitary star in the equatorial constellation of Hydra. It was also given the Flamsteed designation 19 Crateris. This magnitude 3.54 star is situated 130 light-years from Earth and has a radius about 10 times that of the Sun. It is radiating 58 times as much luminosity as the Sun.
V Hydrae is a carbon star in the constellation Hydra. To date perhaps uniquely in our galaxy it has plasma ejections/eruptions on a grand scale that could be caused by its near, unseen companion.
Sigma Cygni, Latinised from σ Cygni, is a blue supergiant star in the constellation Cygnus. Its apparent magnitude is 4.2. It belongs to the Cygnus OB4 stellar association and is located approximately 3,300 light years away from Earth.
Theta Hydrae, Latinized from θ Hydrae, is a binary star system in the constellation Hydra. It is visible to the naked eye with an apparent visual magnitude of 3.9. The star system has a high proper motion with an annual parallax shift of 28.4 mas, indicating a distance of about 115 light years. Theta Hydrae forms a double with a magnitude 9.9 star located at an angular separation of 29 arcseconds.
Eta Hydrae is a star in the equatorial constellation of Hydra. With an apparent visual magnitude of 4.3, it is visible to the naked eye. However, it is the faintest of the five stars that form the "head" of the hydra. Based upon an annual parallax shift of 5.56 mas, it is located roughly 590 light years from the Sun.
Phi3 Hydrae is a binary star in the equatorial constellation of Hydra. It originally received the Flamsteed designation of 2 Crateris before being placed in the Hydra constellation. Based upon an annual parallax shift of 15.49 mas as seen from Earth, it is located around 211 light years from the Sun. It is visible to the naked eye with an apparent visual magnitude of 4.90. It forms a triangle with the fainter φ1 Hydrae and φ2 Hydrae, between μ Hydrae and ν Hydrae.
Omega Hydrae, Latinised from ω Hydrae, is a golden-hued star in the equatorial constellation of Hydra, located to the west-southwest of the brighter star Zeta Hydrae. Based upon an annual parallax shift of just 3.64 mas as seen from Earth, it is located roughly 900 light-years from the Sun. It is faintly visible to the naked eye with an apparent visual magnitude of 5.00.
Phi1 Hydrae, Latinized from φ1 Hydrae, is a yellow-hued star in the constellation Hydra. Its apparent magnitude is 7.61, making it too faint to be seen with the naked eye. Based upon an annual parallax shift of 12.3 mas as seen from Earth, it is located about 266 light years from the Sun. It forms a triangle with the brighter φ2 Hydrae and φ3 Hydrae, between μ Hydrae and ν Hydrae.
3 Puppis is a supergiant star in the constellation Puppis. It is a very rare A[e] supergiant, referred to as a B[e] star despite its spectral classification, and its apparent magnitude is 3.93.
W Canis Majoris is a carbon star in the constellation Canis Major. A cool star, it has a surface temperature of around 2,900 K and a radius 251 times that of the Sun, with a bolometric absolute magnitude of −4.13 and distance estimated at 443 or 445 parsecs based on bolometric magnitude or radius. The Gaia Data Release 2 parallax of 1.8049±0.1454 milliarcseconds implies a distance of about 555 parsecs.
TW Horologii is a carbon star and semiregular variable in the southern constellation of Horologium, near the eastern constellation border with Reticulum. It has a ruddy hue and, with an apparent visual magnitude that ranges from 5.52 down to 5.95, is visible to the naked eye and one of the brightest carbon stars. Based on parallax measurements, it is located at a distance of approximately 1,370 light years from the Sun. It is drifting further away with a radial velocity of +14 km/s. In the past this star has been considered a member of the open cluster NGC 1252, but this now seems unlikely.
S Scuti is a carbon star located in the constellation Scutum. Parallax measurements by Hipparcos put it at a distance of approximately 1,300 light-years. Its apparent magnitude is 6.80, making it not quite bright enough to be seen with the naked eye.
HS Hydrae is a triple star system in the equatorial constellation of Hydra. The inner pair were an eclipsing binary during the period 1920 until 2019, with HS Hya being the variable star designation. With a base apparent visual magnitude of 8.08, HS Hya is too dim to be viewed with the naked eye. During the primary eclipse, the magnitude dropped to 8.61; the secondary eclipse lowered the magnitude to 8.55. Based on parallax measurements, the system is located at a distance of approximately 335 light years from the Sun. It is drifting closer with a mean radial velocity of −7 km/s.
LQ Hydrae is a single variable star in the equatorial constellation of Hydra. It is sometimes identified as Gl 355 from the Gliese Catalogue; LQ Hydrae is the variable star designation, which is abbreviated LQ Hya. The brightness of the star ranges from an apparent visual magnitude of 7.79 down to 7.86, which is too faint to be readily visible to the naked eye. Based on parallax measurements, this star is located at a distance of 59.6 light years from the Sun. It is drifting further away with a radial velocity of 7.6 km/s.
