Beta Hydri

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Beta Hydri
Stellar characteristics
Right ascension (Epoch J2000)00h 25m 45.07s
Declination (Epoch J2000)–77° 15' 15.3"
Spectral typeG2 IV
Distance from Sol24.33 ± 0.02 ly
Other designationsLucida, Bet Hyi, Gl 19, HR 98, CD -77°15, HD 2151, LHS 6, LTT 226, GCTP 69, SAO 255670, CP(D)-77 16, FK5 11, LPM 22, LFT 43, HIP 2021
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Beta Hydri is the closest subgiant to Sol. Aside from the astronomical interest in studying a subgiant star, Beta Hydri features in the source material of interest to "Stellvia" Fen (not to be confused with the Stellvian faction).

SolStation Data

The data in this section was copied from

System Summary

This star is located about 24.4 light-years (ly) away from our Sun, Sol. It lies in the southeastern corner[1] of Constellation Hydrus, the Serpent or Water Snake -- southeast of NGC 104 and southwest of Alpha Hydri. Possibly known to some observers as Lucida (or "luz" for the brightest star in any particular constellation) although it is slightly dimmer than Alpha Hydri, Beta Hydri is clearly visible with the naked eye as the nearest conspicuous star to the South Pole, about 12 degrees distant. Beta Hydri is also the closest confirmed subgiant star to Sol and one of the older as well as highly evolved stars of the Sun's spectral class in the Solar neighborhood. It is a member of the Zeta Herculis stellar moving group.

The Star

Beta Hydri is a yellow-orange main sequence dwarf star of spectral and luminosity type G2 IV. This star may have 1.1 times Sol's mass, 1.46 times its diameter[2], and about 3.53 times its luminosity. It may be from 49 to 100 percent as enriched as Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron[3]. According to the Yale Bright Star Catalogue, 1991 5th Revised Edition notes entry for HR 98, however, the star has a lithium/calcium ratio that is 10 times Sol's. Based on updated distance data from the European HIPPARCOS satellite, Dravins et al (1998) presented a paper at a Hipparcos Conference in Venice (pdf) that revises Beta Hydri's age to about 6.7 billion years with an associated mass estimate of 1.1 times that of Sol's mass.

A New Suspected Variable star designated NSV 161, Beta Hydri is also unusually bright for its spectral type. It appears to be a subgiant star that is evolving off the main sequence, as it begins to fuse increasing amounts of helium "ash" mixed with hydrogen at its core. More information about this star can be found at Dainis Dravins' web page on stellar activity and Beta Hydri.

Hunt for Substellar Companions

In 1993, Murdoch et al noted that Beta Hydri appears to exhibit a low amplitude variability with a period of 45 days. This variability may be caused by the presence of a substellar companion. Since Beta Hydri has become a subgiant, it is possible that any planet that held Earth-like conditions earlier in the system's past has now become too hot to support Earth-type life, but that a colder Mars-type planet has become more Earth-like. Today, the distance from the star where an Earth-type planet would be "comfortable" with liquid water is centered around 1.9 AUs -- between the orbital distance of Mars and the inner boundary of the Main Asteroid Belt in the Solar System. Based on an estimated stellar mass for Beta Hydri about 1.1 times Sol's, the orbital period of such a planet around Beta Hydri would be about 2.5 Earth years.

As a subgiant star subject to pulsations which affect careful measurements of variations in radial velocity caused by the gravitational pull of substellar companions, astronomers would find it very difficult to detect any Earth-type planet around Beta Hydri using present methods. Within a decade, however, astronomers are hoping to use NASA's Terrestrial Planet Finder (TPF) and the ESA's Darwin planned groups of observatories to search for a rocky inner planet in the so-called "habitable zone" (HZ) around this star.

Closest Neighbors

The following star systems are located within 10 light-years of Beta Hydri.

9 Stars of Interest to Beta Hydri Fen
Star System Distance from
Beta Hydri
Travel Time Interwave Lag
L 49-19 4.5 ly 3.29 days 3.94 hours
CD -68°41 5.1 ly 3.73 days 4.47 hours
L 119-44 6.1 ly 4.46 days 5.35 hours
Zeta Tucanae 6.7 ly 4.89 days 5.87 hours
CD -76°1182 8.7 ly 6.36 days 7.63 hours
HIP 31292 9.2 ly 6.72 days 8.06 hours
Delta Pavonis 9.3 ly 6.79 days 8.15 hours
HIP 31293 9.9 ly 7.23 days 8.68 hours
p Eridani 10.0 ly 7.30 days 8.77 hours

Known Places Around Beta Hydri

A star that's older than Sol, far less stable and unlikely to have anything useful to a colony. Plus if the thing finally drops off the main sequence it'll fry everything in the system fool enough to stick around. No offense, but colonizing around Beta Hydri strikes me as the Fen equivalent of the Norse colonies in Greenland: an elaborate way of killing yourself.

—Gen. Malaclypse Fnord, VVS, 7 June 2014


  1. 00:25:45.08-77:15:15.28, ICRS 2000.0
  2. Johnson and Wright, 1983, page 645
  3. Cayrel de Strobel et al, 1991, page 4