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List of stars in Hydra
List of stars in Hydra
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This is the list of notable stars in the constellation Hydra, sorted by decreasing brightness.

Name B F G. Var HD HIP RA Dec vis.
mag. 		abs.
mag. 		Dist. (ly) Sp. class Notes
Alphard α 30 140 81797 46390 09h 27m 35.25s −08° 39′ 31.3″ 1.99 −1.69 177 K3III Alfard, Kalbelaphard, Cor Hydrae, Soheil al Fard, Soheil Solitarius[1]
γ Hya γ 46 345 115659 64962 13h 18m 55.25s −23° 10′ 17.1″ 2.99 −0.05 132 G8III Dhanab al Shudja; Cauda Hydrae
ζ Hya ζ 16 77 76294 43813 08h 55m 23.68s +05° 56′ 43.9″ 3.11 −0.21 151 G8III-IV Hydrobius; Minazal V
ν Hya ν 254 93813 52943 10h 49m 37.43s −16° 11′ 38.9″ 3.11 −0.03 138 K0/K1III
π Hya π 49 368 123123 68895 14h 06m 22.27s −26° 40′ 55.3″ 3.25 0.79 101 K2III
ε Hya ε 11 59 74874 43109 08h 46m 46.65s +06° 25′ 08.1″ 3.38 0.29 135 G0III-IV Ashlesha, BY Draconis variable
ξ Hya ξ 288 100407 56343 11h 33m 00.26s −31° 51′ 27.1″ 3.54 0.55 129 G8III
λ Hya λ 41 201 88284 49841 10h 10m 35.40s −12° 21′ 13.8″ 3.61 0.88 115 K0III
μ Hya μ 42 221 90432 51069 10h 26m 05.51s −16° 50′ 09.9″ 3.83 −0.58 248 K4III
θ Hya θ 22 108 79469 45336 09h 14m 21.79s +02° 18′ 54.1″ 3.89 0.91 129 B9.5V
ι Hya ι 35 170 83618 47431 09h 39m 51.33s −01° 08′ 33.6″ 3.90 −0.74 276 K3IIIvar Ukdah;[2] Ukdah IV
30 Mon C (30) 19 71155 41307 08h 25m 39.67s −03° 54′ 22.9″ 3.91 0.99 125 A0V
υ1 Hya υ1 39 178 85444 48356 09h 51m 28.68s −14° 50′ 47.6″ 4.11 −0.51 273 G6/G8III Zhang, has a brown dwarf companion
δ Hya δ 4 36 73262 42313 08h 37m 39.41s +05° 42′ 13.7″ 4.14 0.44 179 A1Vnn Lisan al Shudja, Lingua Hydri[1]
β Hya β 301 103192 57936 11h 52m 54.56s −33° 54′ 29.3″ 4.29 −0.96 365 Ap Si α2 CVn variable
η Hya η 7 49 74280 42799 08h 43m 13.49s +03° 23′ 55.2″ 4.30 −1.48 466 B3V... Minazal II; β Cep variable
12 Hya D 12 60 74918 43067 08h 46m 22.53s −13° 32′ 51.7″ 4.32 0.11 227 G8III
ρ Hya ρ 13 64 75137 43234 08h 48m 25.98s +05° 50′ 16.4″ 4.35 −0.72 337 A0Vn Minazal IV
58 Hya E 58 387 130694 72571 14h 50m 17.47s −27° 57′ 36.8″ 4.42 −0.44 305 K3III Solitaire[3]
σ Hya σ 5 42 73471 42402 08h 38m 45.45s +03° 20′ 29.3″ 4.45 −0.72 352 K2III Minhar al Shija, Al Minliar al Shuja, Minchir
τ2 Hya τ2 32 152 82446 46776 09h 31m 58.93s −01° 11′ 04.8″ 4.54 −1.20 459 A3V Ukdah;[2] Ukdah II
τ1 Hya τ1 31 145 81997 46509 09h 29m 08.84s −02° 46′ 08.2″ 4.59 3.43 56 F6V Ukdah;[2] Ukdah I
υ2 Hya υ2 40 194 87504 49402 10h 05m 07.49s −13° 03′ 52.8″ 4.60 −0.05 277 B8V
31 Mon F (31) 51 74395 42835 08h 43m 40.38s −07° 14′ 01.4″ 4.63 −1.71 604 G2Ib
2 Sex (2) 168 83425 47310 09h 38m 27.39s +04° 38′ 57.9″ 4.68 0.06 274 K3III
ο Hya ο 293 101431 56922 11h 40m 12.82s −34° 44′ 40.8″ 4.70 −1.21 495 B9V
HD 81799 G 141 81799 46371 09h 27m 18.30s −22° 20′ 36.3″ 4.72 1.06 176 K1III
HD 83953 I 174 83953 47522 09h 41m 17.03s −23° 35′ 29.5″ 4.76 −1.16 497 B5V
26 Hya 26 122 80499 45751 09h 19m 46.40s −11° 58′ 29.6″ 4.77 −0.19 320 G8III
51 Hya k 51 375 125932 70306 14h 23m 05.91s −27° 45′ 13.4″ 4.78 1.14 175 K3III
27 Hya P 27 124 80586 45811 09h 20m 29.03s −09° 33′ 20.3″ 4.80 0.43 243 G8III-IV+... unconfirmed planet?
9 Hya 9 47 74137 42662 08h 41m 43.33s −15° 56′ 35.3″ 4.87 0.89 204 K0IIICN...
HD 85859 181 85859 48559 09h 54m 12.44s −25° 55′ 56.9″ 4.87 −0.19 336 K2III
HD 92036 241 92036 51979 10h 37m 13.80s −27° 24′ 45.7″ 4.87 −0.97 479 M1III
U Hya 240 U 92055 52009 10h 37m 33.25s −13° 23′ 04.0″ 4.89 −1.16 528 C 240 G. Hya. Carbon star
φ Hya φ, φ3 242 92214 52085 10h 38m 35.01s −16° 52′ 35.9″ 4.91 0.72 225 G8III 242 G. Hya
χ1 Hya χ1 264 96202 54204 11h 05m 20.03s −27° 17′ 36.9″ 4.92 1.73 142 F3IV/V
HD 84117 175 84117 47592 09h 42m 14.67s −23° 54′ 58.4″ 4.93 4.07 49 G0V nearby
17 Crt (17) 284 100286 56280 11h 32m 16.42s −29° 15′ 40.9″ 4.93 2.80 87 F8V
HD 85951 183 85951 48615 09h 54m 52.24s −19° 00′ 33.4″ 4.94 −1.74 706 K5III Felis
ψ Hya ψ 45 341 114149 64166 13h 09m 03.28s −23° 07′ 04.7″ 4.94 0.69 231 K0III
52 Hya l 52 379 126769 70753 14h 28m 10.44s −29° 29′ 29.7″ 4.97 −0.56 415 B7/B8V
6 Hya a 6 44 73840 42509 08h 40m 01.52s −12° 28′ 31.3″ 4.98 −0.57 419 K3III
ω Hya ω 18 95 77996 44659 09h 05m 58.38s +05° 05′ 32.4″ 4.99 −2.86 1212 K2II-III
160 G. Hya 160 82734 46880 09h 33m 12.47s −21° 06′ 56.7″ 5.02 −0.03 334 K0III
κ Hya κ 38 173 83754 47452 09h 40m 18.38s −14° 19′ 56.1″ 5.07 −0.92 515 B4IV/V Al Sharāsīf[4]
50 Hya 50 370 124206 69415 14h 12m 46.03s −27° 15′ 40.0″ 5.07 0.83 229 K2III
44 Hya 44 230 91550 51718 10h 34m 00.89s −23° 44′ 42.8″ 5.08 −1.36 633 K5III
II Hya 298 102620 57613 11h 48m 45.11s −26° 44′ 59.1″ 5.10 −0.72 477 M4III
HD 100393 (18) 287 100393 56332 11h 32m 54.15s −31° 05′ 14.0″ 5.13 −0.58 453 M1/M2III 18 Crateris
54 Hya m 54 382 129926 72197 14h 46m 00.18s −25° 26′ 34.5″ 5.15 2.73 99 F0V + G/K
HD 101666 (26) 295 101666 57047 11h 41m 43.95s −32° 29′ 57.6″ 5.20 −0.40 430 K5III 26 Crateris
47 Hya 47 365 121847 68269 13h 58m 31.18s −24° 58′ 19.8″ 5.20 0.11 339 B8V
HD 94388 b3 (6) 257 94388 53252 10h 53m 29.48s −20° 08′ 17.3″ 5.23 2.75 102 F6V 6 Crateris
56 Hya 56 385 130259 72357 14h 47m 44.78s −26° 05′ 14.9″ 5.23 0.19 331 G8/K0III
23 Hya 23 112 79910 45527 09h 16m 41.72s −06° 21′ 11.4″ 5.24 0.58 279 K2III
303 G. Hya 303 103462 58082 11h 54m 42.51s −25° 42′ 50.6″ 5.26 0.48 295 G8III
61 G. Hya 61 74988 43142 08h 47m 15.01s −01° 53′ 49.4″ 5.28 0.19 339 A3V
14 Hya 14 67 KX 75333 43305 08h 49m 21.74s −03° 26′ 34.7″ 5.30 −0.34 438 B9MNp... KX Hya; α2 CVn variable
200 G. Hya 200 88215 49809 10h 10m 05.96s −12° 48′ 56.4″ 5.30 3.12 89 F2/F3IV/V
1 G. Hya 1 68312 40107 08h 11m 33.03s −07° 46′ 20.9″ 5.36 0.43 316 G8III
142 G. Hya 142 81809 46404 09h 27m 46.92s −06° 04′ 15.7″ 5.38 2.91 102 G2V
328 G. Hya 328 109799 61621 12h 37m 42.23s −27° 08′ 19.2″ 5.41 2.72 113 F0V
HD 96819 (10) 271 96819 54477 11h 08m 44.05s −28° 04′ 50.2″ 5.43 1.61 189 A1V 10 Crateris
HD 93397 b1 (3) 249 93397 52737 10h 46m 52.06s −17° 17′ 48.6″ 5.44 1.30 219 A3V 3 Crateris
330 G. Hya 330 110666 62131 12h 44m 00.55s −28° 19′ 25.9″ 5.46 0.03 397 K3III
20 Hya 20 103 78732 44961 09h 09m 35.58s −08° 47′ 15.5″ 5.47 −1.00 642 G8II
HD 122430 367 122430 68581 14h 02m 22.80s −27° 25′ 47.1″ 5.47 −0.15 434 K2/K3III has a planet (b)
24 Hya 24 114 79931 45526 09h 16m 41.38s −08° 44′ 41.1″ 5.49 −1.14 689 B9III
15 Hya 15 70 75737 43496 08h 51m 34.44s −07° 10′ 38.0″ 5.55 −0.33 488 A4m
33 Hya A 33 163 82870 46982 09h 34m 32.64s −05° 54′ 53.3″ 5.56 −1.04 681 K1III Ukdah;[2] Ukdah III
323 G. Hya 323 108323 60735 12h 26m 51.69s −32° 49′ 48.2″ 5.56 −0.42 511 B9V
224 G. Hya 224 90957 51364 10h 29m 29.01s −29° 39′ 49.9″ 5.58 0.21 387 K3III
195 G. Hya 195 87808 49569 10h 07m 09.49s −17° 08′ 29.7″ 5.59 0.48 343 K4III
225 G. Hya 225 91120 51491 10h 30m 59.86s −13° 35′ 18.5″ 5.59 −0.28 487 B8/B9IV/V
2 Hya 2 23 LM 71297 41375 08h 26m 27.23s −03° 59′ 14.3″ 5.60 1.97 173 A5III-IV LM Hya; δ Sct variable
19 Hya 19 99 78556 44883 09h 08m 42.19s −08° 35′ 22.2″ 5.60 −1.60 898 B9.5III
28 Hya 28 134 81420 46221 09h 25m 24.04s −05° 07′ 02.6″ 5.60 −0.98 675 K5III
1 Hya 1 15 70958 41211 08h 24m 35.14s −03° 45′ 04.2″ 5.61 3.44 89 F3V
55 Hya 55 384 130158 72323 14h 47m 22.56s −25° 37′ 27.2″ 5.61 −0.76 613 B9IV/V
92 G. Hya 92 77353 44356 09h 01m 58.02s −00° 28′ 58.2″ 5.64 −0.73 613 K0III
333 G. Hya 333 111295 62500 12h 48m 26.36s −27° 35′ 50.0″ 5.65 0.80 304 G8III
59 Hya 59 92 132219 73284 14h 58m 39.29s −27° 39′ 26.3″ 5.65 0.50 350 A6IV
148 G. Hya 148 82077 46511 09h 29m 12.65s −20° 44′ 56.9″ 5.66 −1.58 913 K4/K5III
χ2 Hya χ2 265 96314 54255 11h 05m 57.55s −27° 17′ 16.1″ 5.69 −1.26 799 B8V 265 G. Hya.; β Lyr variable
350 G. Hya 350 117716 66065 13h 32m 35.96s −28° 41′ 33.8″ 5.69 1.61 214 A0/A1V
56 G. Hya 56 74794 43026 08h 46m 02.45s −02° 02′ 55.6″ 5.70 1.04 278 K0III:
193 G. Hya 193 87427 49339 10h 04m 21.02s −24° 17′ 08.1″ 5.70 1.23 255 F0V
259 G. Hya 259 95221 53699 10h 59m 13.74s −33° 44′ 14.8″ 5.70 2.27 159 F2V
236 G. Hya 236 91889 51933 10h 36m 32.22s −12° 13′ 42.6″ 5.71 3.76 80 F7V
HD 100893 (22) 291 100893 56620 11h 36m 34.92s −33° 34′ 11.9″ 5.71 0.54 352 K0III 22 Crateris
3 Hya 3 35 HV 72968 42146 08h 35m 28.21s −07° 58′ 56.4″ 5.72 1.14 268 A1spe... HV Hya; α2 CVn variable
107 G. Hya 107 79181 45158 09h 11m 58.77s −19° 44′ 51.9″ 5.72 0.90 300 G8III
102 G. Hya 102 78702 44923 09h 09m 04.25s −18° 19′ 43.0″ 5.73 1.22 260 A0/A1V
351 G. Hya 351 118349 66400 13h 36m 48.51s −26° 29′ 42.8″ 5.73 0.36 386 A7V+...
17 G. Hya 17 71095 41299 08h 25m 35.55s +02° 06′ 08.1″ 5.74 −0.59 601 K5III
156 G. Hya 156 82573 46813 09h 32m 20.43s −19° 24′ 01.2″ 5.74 0.58 351 A4III
80 G. Hya 80 76376 43798 08h 55m 12.42s −18° 14′ 28.3″ 5.75 0.17 425 K2/K3III
101 G. Hya 101 78668 44936 09h 09m 11.50s −12° 21′ 27.7″ 5.76 0.01 460 G6III
57 Hya 57 386 130274 72378 14h 47m 57.56s −26° 38′ 46.1″ 5.76 0.14 434 B9.5V
48 Hya 48 366 122066 68390 14h 00m 00.25s −25° 00′ 36.6″ 5.77 1.98 187 F6V
121 G. Hya 121 80479 45743 09h 19m 33.11s −15° 50′ 04.3″ 5.79 0.34 400 K1/K2III
272 G. Hya 272 97023 54561 11h 09m 53.38s −32° 22′ 02.8″ 5.79 0.69 342 A1V also known as HR 4339
33 G. Hya 33 72660 42028 08h 34m 01.64s −02° 09′ 05.8″ 5.80 0.80 326 A1V
88 G. Hya 88 76932 44075 08h 58m 43.78s −16° 07′ 59.7″ 5.80 4.16 70 F7/F8IV/V
354 G. Hya 354 118646 66563 13h 38m 42.13s −29° 33′ 38.4″ 5.81 2.36 160 F3V
357 G. Hya 357 119752 67143 13h 45m 36.94s −26° 06′ 57.5″ 5.81 1.08 287 A0V
118 G. Hya 118 80050 45559 09h 17m 07.73s −14° 34′ 26.6″ 5.83 0.44 389 K0III
60 Hya 60 393 132851 73566 15h 02m 06.38s −28° 03′ 37.9″ 5.83 0.84 325 A4IV
300 G. Hya 300 103026 57841 11h 51m 41.62s −30° 50′ 02.7″ 5.85 3.36 102 F8V
150 G. Hya 150 82232 46618 09h 30m 22.54s −15° 34′ 37.9″ 5.86 1.45 249 K2III
329 G. Hya 329 109960 61720 12h 39m 03.48s −30° 25′ 20.5″ 5.86 −0.26 547 K2/K3III
252 G. Hya 252 93657 52841 10h 48m 14.13s −31° 41′ 16.3″ 5.87 0.29 426 A1V
374 G. Hya 374 125276 69965 14h 19m 01.13s −25° 48′ 58.7″ 5.87 4.62 58 F7Vw
HD 72561 32 72561 42008 08h 33m 43.49s +04° 45′ 25.3″ 5.89 −5.22 5433 G5III
14 G. Hya 14 70652 41080 08h 22m 54.10s −07° 32′ 35.3″ 5.92 −1.11 832 M1III
162 G. Hya 162 82747 46897 09h 33m 26.10s −22° 51′ 50.5″ 5.92 1.12 297 B9.5V
HD 103596 304 103596 58158 11h 55m 40.13s −28° 28′ 37.3″ 5.93 0.11 477 K4III 29 Crateris
84 G. Hya 84 76579 43899 08h 56m 34.13s −16° 42′ 31.3″ 5.95 −0.82 738 K3III
158 G. Hya 158 82660 46859 09h 32m 55.78s −13° 31′ 00.5″ 5.95 −1.06 823 K4III
HD 100623 (20) 289 100623 56452 11h 34m 29.95s −32° 50′ 00.0″ 5.96 6.06 31 K0V 20 Crateris
27 G. Hya 27 71766 41597 08h 28m 51.01s −09° 44′ 54.9″ 6.01 −1.39 985 F2III
HD 76151 75 76151 43726 08h 54m 18.19s −05° 26′ 04.3″ 6.01 4.85 56 G3V
136 G. Hya 136 81567 46288 09h 26m 22.31s −01° 27′ 50.6″ 6.01 −1.14 876 K3III
209 G. Hya 209 89455 50536 10h 19m 16.88s −12° 31′ 41.2″ 6.01 1.89 217 A8III
φ2 Hya φ2 234 91880 51905 10h 36m 16.68s −16° 20′ 39.6″ 6.01 −1.35 967 M1III
16 G. Hya 16 70937 41214 08h 24m 36.42s −04° 43′ 00.7″ 6.03 1.98 211 F2V
6 G. Hya 6 70013 40818 08h 19m 49.85s +03° 56′ 53.1″ 6.04 −0.21 579 G8III
227 G. Hya 227 91280 51551 10h 31m 48.73s −28° 14′ 13.5″ 6.04 2.90 138 F6/F7V
243 G. Hya 243 92245 52113 10h 38m 50.44s −12° 26′ 37.1″ 6.04 0.83 359 A0Vn
361 G. Hya 361 121156 67890 13h 54m 16.75s −28° 34′ 09.9″ 6.05 2.04 206 K2III
260 G. Hya 260 95456 53818 11h 00m 40.84s −31° 50′ 22.6″ 6.06 3.59 102 F8V
90 G. Hya 90 77250 44315 09h 01m 31.40s +05° 38′ 27.6″ 6.08 −0.84 789 F3IV+...
179 G. Hya 179 85519 48396 09h 51m 59.53s −16° 32′ 04.6″ 6.08 0.66 395 K0III
65 G. Hya 65 75140 43204 08h 48m 04.87s −06° 33′ 31.5″ 6.09 −0.46 667 K0
322 G. Hya 322 108110 60603 12h 25m 18.41s −27° 44′ 56.4″ 6.09 −0.38 643 K3III
21 Hya 21 106 KW 79193 45184 09h 12m 26.05s −07° 06′ 35.6″ 6.10 1.51 269 A3m KW Hya; Algol variable
231 G. Hya 231 91706 51795 10h 34m 57.76s −23° 10′ 34.8″ 6.10 2.09 207 F6V
372 G. Hya 372 124576 69623 14h 15m 01.28s −29° 16′ 54.7″ 6.10 −0.54 695 A1V
155 G. Hya 155 82543 46840 09h 32m 41.41s +01° 51′ 51.3″ 6.11 0.58 416 F7IV-V
OY Hya (188 G. Hya) 188 OY 86612 48943 09h 59m 06.32s −23° 57′ 02.8″ 6.11 −0.31 628 B5V Be star
9 G. Hya 9 70148 40859 08h 20m 17.01s −05° 19′ 47.4″ 6.12 0.12 516 K2III
73 G. Hya 73 75916 43580 08h 52m 30.74s −13° 13′ 58.6″ 6.12 1.04 338 K1III
154 G. Hya 154 82477 46768 09h 31m 55.77s −10° 22′ 13.4″ 6.12 0.92 358 K0
157 G. Hya 157 82638 46869 09h 33m 02.00s −08° 30′ 19.0″ 6.12 0.72 393 K0
217 G. Hya 217 89911 50790 10h 22m 12.96s −19° 51′ 59.7″ 6.12 −0.55 704 A0V
10 Hya 10 52 74591 42931 08h 45m 01.28s +05° 40′ 50.1″ 6.13 2.12 207 A6V
81 G. Hya 81 76494 43902 08h 56m 37.04s +04° 14′ 11.7″ 6.13 −1.34 1016 G8II-III
153 G. Hya 153 82428 46744 09h 31m 38.97s −10° 33′ 07.1″ 6.13 2.46 177 F0Vn
13 G. Hya 13 70574 41036 08h 22m 30.20s −06° 10′ 45.0″ 6.14 2.07 212 A8IV
105 G. Hya 105 79108 45167 09h 12m 12.91s +03° 52′ 01.2″ 6.14 0.83 376 A0V
146 G. Hya 146 82043 46529 09h 29m 24.47s −02° 12′ 18.6″ 6.14 0.32 475 F0III
MO Hya 334 MO 111786 62788 12h 51m 57.97s −26° 44′ 18.1″ 6.14 2.24 196 A0III δ Sct variable
363 G. Hya 363 121699 68177 13h 57m 27.75s −23° 01′ 21.5″ 6.14 −0.17 596 K2/K3III
HD 100307 286 100307 56293 11h 32m 23.34s −26° 44′ 48.7″ 6.15 −0.59 728 M2III
NS Hya 96 NS 78196 44738 09h 06m 59.95s +01° 27′ 45.8″ 6.16 −1.25 991 M1III
315 G. Hya 315 105686 59307 12h 10m 02.58s −34° 42′ 17.0″ 6.16 1.14 329 A0V
302 G. Hya 302 103266 57971 11h 53m 26.87s −35° 03′ 59.7″ 6.17 1.78 246 A2V
8 G. Hya 8 70110 40858 08h 20m 12.98s −00° 54′ 32.8″ 6.18 3.13 133 F9V
37 G. Hya 37 73281 42299 08h 37m 27.17s −04° 56′ 02.4″ 6.18 0.79 391 K0
89 G. Hya 89 77084 44162 08h 59m 39.94s −19° 12′ 28.1″ 6.19 3.20 129 F5IV/V
359 G. Hya 359 120455 67523 13h 50m 06.54s −29° 04′ 52.5″ 6.19 0.97 361 A0V
LV Hya 305 LV 103789 58272 11h 57m 03.78s −33° 18′ 55.6″ 6.20 0.88 378 B9.5V α2 CVn variable
HD 95698 (8) 261 95698 53963 11h 02m 24.41s −26° 49′ 52.3″ 6.21 2.59 173 A9III/IV 8 Crateris
356 G. Hya 356 119623 67071 13h 44m 45.70s −25° 30′ 03.2″ 6.21 −0.47 706 K3III
58 G. Hya 58 74860 43035 08h 46m 06.89s −11° 00′ 24.5″ 6.22 −4.13 3835 K5III
182 G. Hya 182 85905 48584 09h 54m 31.83s −22° 29′ 14.8″ 6.23 0.50 457 A2/A3III
205 G. Hya 205 88699 50066 10h 13m 19.48s −27° 01′ 44.3″ 6.23 0.74 409 A9m...
311 G. Hya 311 105078 59008 12h 05m 56.69s −35° 41′ 38.2″ 6.23 −0.51 728 B7V
371 G. Hya 371 124281 69458 14h 13m 13.25s −26° 36′ 44.2″ 6.23 −0.46 709 K0III
199 G. Hya 199 88182 49802 10h 09m 56.49s −12° 05′ 42.9″ 6.24 1.74 259 A5m
245 G. Hya 245 92770 52391 10h 42m 31.38s −13° 58′ 28.4″ 6.24 −0.53 738 K3/K4III:
147 G. Hya 147 82074 46543 09h 29m 32.43s −04° 14′ 47.4″ 6.25 2.57 177 G6IV
159 G. Hya 159 82674 46893 09h 33m 19.94s −07° 11′ 24.5″ 6.25 0.70 421 K0
197 G. Hya 197 88025 49689 10h 08m 35.45s −15° 36′ 43.0″ 6.25 0.01 578 A0V
149 G. Hya 149 82180 46569 09h 29m 49.88s −23° 20′ 43.2″ 6.26 −2.26 1646 K2/K3III
144 G. Hya 144 81980 46504 09h 29m 02.34s −01° 15′ 24.9″ 6.27 1.47 297 F0Vn
185 G. Hya 185 86266 48763 09h 56m 46.89s −26° 32′ 59.1″ 6.27 2.06 227 A4V
391 G. Hya 391 131919 73171 14h 57m 13.72s −29° 09′ 27.4″ 6.28 0.12 557 B8/B9V
235 G. Hya 235 91881 51885 10h 36m 04.51s −26° 40′ 31.0″ 6.29 3.07 143 F5V
126 G. Hya 126 80719 45854 09h 20m 55.46s −15° 37′ 03.2″ 6.30 2.88 158 F6V
192 G. Hya 192 87344 49321 10h 04m 02.83s −18° 06′ 05.1″ 6.30 0.47 477 B8V
HQ Hya 7 HQ 69997 40766 08h 19m 15.11s −10° 09′ 57.0″ 6.31 1.14 353 F3IIIp δ Sct variable
37 Hya 37 171 OW 83650 47427 09h 39m 47.42s −10° 34′ 13.0″ 6.31 −1.33 1098 A0Vn OW Hya; 171 G. Hya.
337 G. Hya 337 112519 63243 12h 57m 33.17s −22° 45′ 12.5″ 6.31 0.83 407 K0III
111 G. Hya 111 79752 45424 09h 15m 24.95s −15° 01′ 29.5″ 6.32 1.18 348 A0V
HD 100953 (23) 292 100953 56657 11h 37m 01.22s −32° 59′ 16.8″ 6.32 2.04 234 F5V 23 Crateris
165 G. Hya 165 83104 47070 09h 35m 33.82s −19° 34′ 59.9″ 6.33 1.63 283 A0V
71 G. Hya 71 75811 43570 08h 52m 24.18s +05° 20′ 25.2″ 6.34 0.22 547 A5V
104 G. Hya 104 79066 45150 09h 11m 55.69s +05° 28′ 07.2″ 6.34 2.81 166 A9IVe...
V335 Hya 316 V335 106198 59588 12h 13m 12.97s −34° 07′ 31.0″ 6.34 −0.89 911 M4/M5Ib/II:
317 G. Hya 317 106257 59622 12h 13m 36.80s −33° 47′ 34.4″ 6.34 0.86 406 A0V
34 G. Hya 34 72908 42142 08h 35m 24.96s +02° 44′ 36.4″ 6.35 0.21 551 G9III
275 G. Hya 275 97393 54725 11h 12m 14.78s −32° 26′ 01.8″ 6.35 −0.23 676 M2/M3III
369 G. Hya 369 124162 69398 14h 12m 24.55s −24° 21′ 48.0″ 6.35 0.49 484 K2III
373 G. Hya 373 125279 69977 14h 19m 07.17s −27° 08′ 28.2″ 6.35 −0.69 834 K5III
206 G. Hya 206 88806 50142 10h 14m 08.98s −23° 48′ 50.3″ 6.36 −1.70 1336 M1III
50 G. Hya 50 74393 42854 08h 43m 59.79s +04° 20′ 04.5″ 6.37 −0.40 738 B9.5III-IV
172 G. Hya 172 83731 47454 09h 40m 20.07s −10° 46′ 09.1″ 6.37 −0.68 838 A2V
29 G. Hya 29 72462 41893 08h 32m 33.39s −15° 01′ 48.7″ 6.38 2.13 231 A7IV/V
320 G. Hya 320 107869 60468 12h 23m 47.82s −30° 20′ 07.4″ 6.39 −0.57 803 K5III
34 Hya 34 167 83373 47249 09h 37m 51.54s −09° 25′ 28.1″ 6.40 1.10 375 A1V
R Hya 347 R 117287 65835 13h 29m 42.82s −23° 16′ 52.9″ 6.40 −2.55 2012 M6/M7e Mira variable
55 G. Hya 55 74688 42951 08h 45m 20.77s −02° 36′ 03.7″ 6.41 1.71 283 F2+...
LO Hya (25 G. Hya) 25 LO 71663 41564 08h 28m 29.16s −02° 31′ 01.6″ 6.42 1.77 278 A5m
66 G. Hya 66 75217 43246 08h 48m 37.48s −01° 02′ 41.4″ 6.42 0.68 458 K0
308 G. Hya 308 104039 58436 11h 58m 54.39s −25° 54′ 31.7″ 6.42 −0.76 891 A1IV/V
364 G. Hya 364 121758 68224 13h 57m 58.86s −25° 59′ 53.1″ 6.42 0.17 579 K1III
26 G. Hya 26 71665 41547 08h 28m 19.78s −08° 48′ 58.3″ 6.43 −0.65 849 K0
74 G. Hya 74 76027 43623 08h 53m 05.35s −16° 57′ 08.5″ 6.43 0.89 417 K1III
274 G. Hya 274 97344 54703 11h 11m 57.86s −26° 48′ 22.1″ 6.43 0.84 427 K0III
332 G. Hya 332 111226 62448 12h 47m 53.67s −24° 51′ 06.3″ 6.43 −0.66 853 B8V
360 G. Hya 360 120690 67620 13h 51m 20.70s −24° 23′ 23.2″ 6.43 4.93 65 G5V
263 G. Hya 263 95857 54030 11h 03m 16.09s −31° 57′ 38.8″ 6.44 −0.38 753 M2/M3III
279 G. Hya 279 98221 55164 11h 17m 38.88s −34° 44′ 14.3″ 6.44 3.09 152 F3V
281 G. Hya 281 99712 55953 11h 27m 58.67s −35° 19′ 43.9″ 6.44 −1.50 1264 K4/K5III
294 G. Hya 294 101563 57001 11h 41m 08.60s −29° 11′ 48.6″ 6.44 3.35 135 G2III/IV
54 G. Hya 54 74685 42981 08h 45m 34.84s +04° 39′ 52.4″ 6.45 0.93 414 K0
117 G. Hya 117 79994 45543 09h 16m 57.05s −11° 06′ 10.6″ 6.45 1.19 368 K0
166 G. Hya 166 83352 47242 09h 37m 45.94s −03° 10′ 14.2″ 6.45 0.74 452 K0
204 G. Hya 204 88595 50013 10h 12m 38.10s −19° 09′ 10.1″ 6.45 3.33 137 F7V
258 G. Hya 258 94619 53387 10h 55m 11.58s −20° 39′ 53.9″ 6.45 0.00 637 K1III
349 G. Hya 349 117718 66060 13h 32m 34.52s −29° 33′ 55.0″ 6.45 3.08 154 F5IV
48 G. Hya 48 74190 42701 08h 42m 09.83s −11° 57′ 57.5″ 6.46 1.13 379 A5m
109 G. Hya 109 79481 45305 09h 14m 03.09s −14° 41′ 41.3″ 6.46 0.26 567 G6/G8III/IV
325 G. Hya 325 109074 61172 12h 32m 04.40s −32° 32′ 01.4″ 6.46 0.25 568 A3V
82 G. Hya 82 76478 43850 08h 55m 54.49s −15° 26′ 22.0″ 6.47 −0.51 813 K2III
213 G. Hya 213 89816 50728 10h 21m 28.70s −23° 42′ 39.2″ 6.47 1.18 373 A4IV/V
270 G. Hya 270 96723 54430 11h 08m 15.77s −29° 58′ 20.8″ 6.47 0.74 457 A1V
3 G. Hya 3 68667 40263 08h 13m 21.79s −01° 09′ 57.2″ 6.48 0.47 519 K0
63 G. Hya 63 75098 43152 08h 47m 21.48s −17° 03′ 10.3″ 6.48 −0.36 762 A2V
100 G. Hya 100 78614 44888 09h 08m 44.52s −16° 16′ 37.8″ 6.48 1.07 394 K0IIICN...
297 G. Hya 297 102438 57507 11h 47m 15.99s −30° 17′ 09.4″ 6.48 5.23 58 G5V
299 G. Hya 299 102888 57749 11h 50m 37.24s −27° 16′ 40.6″ 6.48 0.57 495 G8III
348 G. Hya 348 117558 65969 13h 31m 33.22s −28° 06′ 45.9″ 6.48 1.78 284 A1V
378 G. Hya 378 126400 70538 14h 25m 47.77s −26° 51′ 07.6″ 6.48 2.05 251 K0III
233 G. Hya 233 91790 51852 10h 35m 38.86s −18° 34′ 08.4″ 6.49 2.20 235 A5IV/V
312 G. Hya 312 105113 59021 12h 06m 05.25s −32° 57′ 38.7″ 6.49 2.94 167 G0V
342 G. Hya 342 114576 64375 13h 11m 39.24s −26° 33′ 06.2″ 6.49 1.23 367 A5V
346 G. Hya 346 117033 65682 13h 28m 01.88s −26° 24′ 08.0″ 6.49 −1.12 1087 K5III
210 G. Hya 210 89747 50693 10h 21m 07.98s −17° 59′ 05.6″ 6.50 2.68 189 F3IV
318 G. Hya 218 106500 59742 12h 15m 06.42s −29° 14′ 13.9″ 6.50 0.75 461 K0III
HD 96700 269 96700 54400 11h 07m 54s −30° 10′ 28″ 6.50 83 G0V have two planets (b and c)
29 Hya 29 139 81728 46365 09h 27m 14.65s −09° 13′ 25.3″ 6.53 −1.48 1304 A2V
HD 82943 164 82943 47007 09h 34m 50.74s −12° 07′ 46.4″ 6.54 4.35 90 G0V has three planets (b, c & d)
HD 94046 b2 (5) 94046 53037 10h 51m 05.99s −18° 19′ 56.0″ 6.56 0.76 471 A3V 5 Crateris
17 Hya 17 79 76370 43822 08h 55m 29.60s −07° 58′ 16.0″ 6.67 1.72 319 A3
14 Lib (14) 131992 73189 14h 57m 31.96s −25° 26′ 30.4″ 6.95 1.56 391 A2/A3V
HD 90156 90156 50921 10h 23m 55.27s −29° 38′ 43.9″ 6.95 5.23 72 G5V has a planet (b); variable star
V Hya V 53085 10h 51m 37.26s −21° 15′ 00.0″ 7.0 C Carbon star
25 Hya 25 80105 45588 09h 17m 29.22s −11° 57′ 42.7″ 7.07 1.50 424 K0
HD 86264 86264 48780 09h 56m 57.84s −15° 53′ 42.4″ 7.42 3.12 237 F7V has a planet (b)
HD 86950 86950 49129 10h 01m 38.0s −17° 19′ 59″ 7.46 551 K1 III has a planet
HD 72659 72659 42030 08h 34m 03.19s −01° 34′ 05.6″ 7.48 3.93 168 G0 has a planet (b)
HD 74156 74156 42723 08h 42m 25.12s +04° 34′ 41.2″ 7.62 3.57 211 G0V has three planets (b, c, & unconfirmed d)
φ1 Hya φ1 43 91369 51614 10h 32m 41.17s −16° 57′ 30.7″ 7.62 3.25 244 G2V
HD 86226 86226 48739 09h 56m 29.84s −24° 05′ 57.8″ 7.93 4.79 139 G2V has a planet (b)
HD 128356 128356 71481 14h 37m 05.0s −25° 48′ 09″ 8.29 85 K3V has a planet
V478 Hya V478 70573 08h 22m 49.95s +01° 51′ 33.6″ 8.70 5.40 149 G1-1.5V has a planet (b)
HD 72892 72892 42098 08h 34m 53.0s −14° 27′ 24″ 8.83 237 G5V has a planet
WASP-166 09h 39m 30.0s −20° 58′ 57″ 9.36 369 F9 has a transiting planet
Gliese 433 56528 11h 35m 26.95s −32° 32′ 23.9″ 9.79 10.01 29 M1.5 has a planet (b)
WASP-51/HAT-P-30 08h 15m 48s +05° 50′ 12″ 10.42 629 F has a transiting planet
GJ 357 47101 09h 36m 01.64s −21° 39′ 38.9″ 10.91 11.13 31 M2.5V has three transiting planets (d)
TW Hya TW 53911 11h 01m 51.91s −34° 42′ 17.0″ 11.1 7.3 184 K8Ve T Tauri star, retracted planet
WASP-25 13h 01m 26.37s −27° 31′ 19.9″ 11.87 5.74 550 G4 has a transiting planet
WASP-175 11h 05m 17.0s −34° 07′ 20″ 12 1905 has a transiting planet
HAT-P-42 09h 01m 23.0s +06° 05′ 50″ 12.17 1458 Lerna; has a transiting planet
WASP-169 08h 29m 33.0s −12° 56′ 41″ 12.2 2081 has a transiting planet
WASP-142 09h 22m 02.0s −23° 56′ 46″ 12.3 2740 F8 has a transiting planet
HAT-P-35 08h 13m 00s +04° 47′ 13″ 12.46 1745 has a transiting planet
WASP-143 09h 23m 23.0s +02° 55′ 57″ 12.6 1115 G1 has a transiting planet
WASP-36 08h 45m 9.0s −08° 01′ 37″ 12.7 1468 G2 has a transiting planet
LHS 3003 14h 56m 38.314s −28° 09′ 47.38″ 17.141 20.9 M7.0V [5][6][7][8][9]
Gliese 3634 10h 58m 35s −31° 08′ 39″ 19.8 65 M2.5 has a planet (b)
WASP-84 08h 44m 26.0s +01° 50′ 36″ 391 K0 has a transiting planet
G 161-71 09h 44m 54.224s −12° 20′ 54.43″ 13.6 43.4 M4.5 [10][11][12][13][14] has one Saturn-mass planet candidate from direct imaging[15]
Table legend:

See also

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References

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Bibliography

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List of stars in Hydra

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The list of stars in Hydra encompasses the numerous stellar objects positioned within the International Astronomical Union (IAU)-defined boundaries of the constellation Hydra, the largest of the 88 modern constellations, spanning 1,303 square degrees across the southern celestial hemisphere. This expansive region, stretching over 100 degrees in length from the border of Cancer to Libra, is visible to observers at latitudes between +54° and -83°, with optimal viewing during spring evenings in the Northern Hemisphere. Although Hydra contains thousands of stars detected by modern telescopes, lists of its stars typically focus on those brighter than magnitude 6—visible to the naked eye—or those with historical designations, including Bayer and Flamsteed notations, totaling around two dozen principal entries. Among the most notable stars in Hydra is Alphard (Alpha Hydrae), the constellation's brightest at 2.0, an evolved orange giant of type K3 III located approximately 177 light-years from , with a radius about 58 times that of the Sun. Other prominent Bayer-designated stars include Gamma Hydrae (magnitude 3.0, a yellow giant 134 light-years away), Zeta Hydrae (magnitude 3.1, an evolved G9 giant 167 light-years distant), Hydrae (magnitude 3.4, a multiple 129 light-years away), and Beta Hydrae (magnitude 4.3, a chemically peculiar B-type star 370 light-years from the Sun). These stars, along with fainter ones like Delta Hydrae (magnitude 4.1, a 160 light-years away) and Nu Hydrae (magnitude 3.1, an orange giant and source 110 light-years distant), represent a diverse array of types, from hot main-sequence stars to cool giants, many of which are variable or binary systems. The IAU has approved nine proper names for stars in Hydra, including Alphard, Minchir (Sigma Hydrae), and Ukdah, reflecting historical and cultural significance in astronomical nomenclature. Such lists serve as references for astronomers and stargazers, drawing from catalogs like the Henry Draper Catalogue and mission data to provide details on positions, magnitudes, distances, and physical properties, aiding in the study of within this vast watery domain of the .

Constellation Background

Location and Visibility

The constellation Hydra spans a vast region of the southern , with boundaries extending from 8^h to 15^h and from about +5° to -30°. This elongated area positions Hydra primarily in the , though its head extends slightly north of the . As the largest of the 88 modern constellations recognized by the , Hydra covers 1,303 square degrees, accounting for approximately 3.16% of the total . Its serpentine shape winds across the sky like a water snake, starting near the constellation Cancer in the north and trailing southward toward Libra and , making it a prominent but sprawling feature. In the , Hydra is best observed from to May, when its body rises high enough in the evening sky for optimal visibility, particularly from latitudes around 40°N where the entire figure can be traced. To locate it, observers can start with the bright star in Virgo and follow the curve southward, or use the distinctive head asterism below Cancer; its proximity to the allows it to be viewed from both the northern and southern hemispheres, though it requires clear southern horizons from northern latitudes. Light pollution significantly hampers the visibility of Hydra, especially from urban areas, as the constellation features relatively few bright stars—its brightest, Alphard, reaches only magnitude 2.0—causing fainter components of its serpentine form to blend into the . In Bortle class 5 or higher skies, only the principal stars remain discernible to the , underscoring the need for dark-sky sites to appreciate its full extent.

Historical and Mythological Context

The constellation Hydra derives its name from the of , a serpentine monster with multiple heads—typically depicted as nine—that guarded the swamps near and was slain by the hero during his second labor, as recounted in ancient texts like Apollodorus's Bibliotheca. The creature's regenerative heads, which grew back when severed unless cauterized, symbolized chaos and immortality, and its placement in the sky was said to commemorate the battle, with nearby constellations like (the crow) and (the cup) representing elements of the myth. In classical astronomy, Hydra was observed and cataloged by around 127 BCE as part of his star measurements, though his work survives primarily through Ptolemy's Almagest (c. 150 CE), where it appears as one of the 48 ancient constellations, described as a vast water snake extending across the southern sky. Ptolemy's depiction emphasized its elongated form, with the head positioned below Cancer and the tail trailing toward Libra, influencing subsequent Greco-Roman that linked it to water deities and seasonal floods. Arabic astronomers during the medieval period adapted the constellation, naming it Al Hayyah ("the snake") or associating its head with Min al-Az'al ("the uninhabited spot"), integrating it into their navigational and astrological traditions while preserving Ptolemaic boundaries. By the , Polish astronomer refined its representation in his Uranographia (1690), featuring intricate engravings that standardized Hydra's serpentine outline in European star charts, separating it from adjacent figures like and . Cultural interpretations extended beyond the West; in traditional Chinese astronomy, Hydra's stars were divided between the Vermilion Bird (Zhu Que) of the southern quadrant—symbolizing summer and the element of fire—and the Azure Dragon (Qing Long) of the east, forming part of the Twenty-Eight Mansions used for imperial calendrics and feng shui.

Stellar Classification and Naming

Bayer and Flamsteed Designations

The Bayer designation system, introduced by German astronomer Johann Bayer in his 1603 star atlas Uranometria, assigns lowercase Greek letters to stars within a constellation, ordered approximately by decreasing brightness, followed by the genitive form of the constellation's Latin name. For Hydra, the largest of the 88 modern constellations spanning over 1,300 square degrees, this results in one of the most extensive sets of designations, with letters ranging from α Hydrae (the brightest star, also known as Alphard) through to later Greek letters and extending into Roman letters such as a Hydrae and b Hydrae when the 24 Greek letters proved insufficient. Bayer's approach cataloged approximately 1,164 stars across all constellations, but Hydra's vast extent led to challenges, including the omission of three stars from the final designations due to identification issues or incomplete mapping at the time. Complementing Bayer's system, the Flamsteed designation was developed through an unofficial edition of English astronomer John Flamsteed's star catalog, later formalized by Joseph Jérôme de Lalande in 1783. These designations assign to stars within each constellation, ordered by increasing rather than brightness, providing a numerical supplement for fainter or additional stars beyond Bayer's lettering capacity—essential in expansive constellations like Hydra, where examples include 27 Hydrae for a star not prominent enough for a Greek letter. In total, Hydra features around 75 stars with either Bayer or Flamsteed designations, highlighting how Flamsteed's method addresses gaps in Bayer's scheme without duplicating primary assignments. In modern astronomy, these historical systems integrate with catalogs like the Henry Draper Catalogue (HD), published between 1918 and 1924, which assigns sequential numbers to over 225,000 stars while incorporating Bayer and Flamsteed identifiers alongside spectral classifications. For Hydra's stars, this allows prefixes such as "K3 III" for α Hydrae in HD entries, enabling precise spectroscopic analysis without altering the original designations, thus bridging early naming conventions with contemporary data on stellar types and properties.

Traditional Names and Catalog Entries

Several stars in the constellation Hydra have retained traditional names rooted in astronomical , which highlight the serpent-like form of the constellation in historical sky maps. Alphard, the proper name for Alpha Hydrae, derives from the Arabic term "al-fard," meaning "the solitary one," alluding to the star's prominent isolation relative to others in the region. Similarly, Minchir, the approved name for Sigma Hydrae, stems from the Arabic "minkhar al-shuja'," translating to "the nostril of the snake," evoking the constellation's reptilian imagery. These names, along with others like Ukdah for Hydrae—derived from the Arabic "al-'uqdah," signifying "the node" or "knot"—were formalized through the (IAU) Working Group on Star Names, which began approving proper names in to preserve cultural and historical heritage in astronomy. The IAU has approved nine proper names for stars in Hydra as of 2021, drawing from diverse cultural traditions such as , Hindu, Chinese, and others. In addition to Alphard, Minchir, and Ukdah, these include Ashlesha for Epsilon Hydrae (from the Sanskrit lunar mansion denoting "the entwiner"), for Nu Hydrae (Latin for "cat," reflecting early catalog associations), Zhang for Upsilon2 Hydrae (from ), Filetdor for WASP-166 (an ), Lerna for HAT-P-42 (a G-type star near the mythological Hydra's location), and Solitaire for 58 Hydrae (a G-type giant). Hydra's stars are extensively documented in specialized astronomical catalogs that facilitate research on variability and multiplicity. The General Catalogue of Variable Stars (GCVS), maintained by the Sternberg Astronomical Institute and updated periodically, includes entries for numerous variable stars in Hydra, providing details on light curves, periods, and classifications. Likewise, the Washington Double Star Catalog (WDS), compiled by the U.S. Naval Observatory, catalogs hundreds of double and multiple star systems within Hydra's boundaries, recording orbital parameters, separations, and historical measurements. Cross-references to these and other catalogs are accessible through databases like (operated by the Centre de Données astronomiques de Strasbourg) and (also from CDS), which aggregate data on over 1,000 stars in Hydra from various surveys, enabling comprehensive queries on positions, identifications, and bibliographic references.

Catalog of Principal Stars

Stars Brighter Than Magnitude 3.0

Hydra features two prominent stars brighter than 3.0, both serving as key navigational points in the southern sky due to their visibility and distinct positions along the constellation's elongated form. These stars, designated by letters, provide essential markers for observers tracing Hydra's serpentine outline from the head near Cancer to the tail near Libra. The following table summarizes their fundamental properties, including apparent magnitudes, spectral classifications, distances, equatorial coordinates (J2000 epoch), color indices, and proper motions derived from astrometry.
Bayer DesignationTraditional Name (V)Spectral TypeDistance (light-years)Coordinates (RA, Dec) (RA, Dec; mas/yr)
α HyaAlphard1.98K3 III18009h 27m 35s, -08° 39' 31"1.45-15.23, +34.37
γ HyaCauda Hydrae3.00G8 III12813h 18m 55s, -23° 10' 17"0.92+67.96, -44.30
Alpha Hydrae, or Alphard, stands as Hydra's brightest star and the only one exceeding second magnitude in the constellation, appearing as an isolated orange giant that dominates the "heart" region of the water serpent. Its name originates from the Arabic al-fard al-shuja', translating to "the solitary one in the serpent," emphasizing its lack of nearby companions of comparable brightness. Gamma Hydrae, positioned at the constellation's tail, is a giant that anchors the southern extent of Hydra, offering a subtle contrast to Alphard's prominence with its steady glow. Known traditionally as Cauda Hydrae in Latin, meaning "the tail of Hydra," this designation highlights its role in delineating the figure's elongated posterior.

Stars Between Magnitude 3.0 and 4.0

The stars in the constellation Hydra with apparent visual magnitudes between 3.0 and 4.0 contribute significantly to its outline for amateur observers under , where they appear as a chain of steady points tracing the serpentine form from the head near Cancer toward the extended body and tail regions. These stars, primarily giants and subgiants of late G and spectral types, are located at distances ranging from about 100 to 250 light-years (as of DR3, 2022), allowing for relatively precise measurements from modern surveys like . Their positions correspond to Flamsteed numbers such as 35 for ζ Hydrae and 17 for ε Hydrae, facilitating precise identification in catalogs. Visibility is optimal in spring for northern latitudes, with these stars reaching altitudes up to 20-30 degrees above the horizon along Hydra's length. The following table summarizes key examples of these stars, including Bayer and Flamsteed designations, apparent magnitudes, distances, spectral types with luminosity classes, and representative radial velocities where measured from spectroscopic data (as of Gaia DR3 and SIMBAD, 2023).
Designation (Bayer/Flamsteed)Apparent MagnitudeDistance (ly)Spectral Type (Luminosity Class)Radial Velocity (km/s)Notes
ζ Hya (35 Hya)3.10153G8.5 III+22.3Orange giant near the head; part of Hydra's "neck."
ν Hya3.11137K1.5 III-1.4Red giant along the body; steady brightness. (Flamsteed 39 Hya)
π Hya (49 Hya)3.28106K2 III+27.2Orange giant; cyanogen-weak.
ε Hya (17 Hya)3.38129G1 III + A8 V+40.5Yellow giant (traditional name Ashlesha); multiple system visible with small telescopes.
ξ Hya (20 Hya)3.54131G7 III-4.6Yellow giant in the mid-body; double star.
λ Hya (14 Hya)3.61109K0 III+19.4Yellow giant toward the tail; multiple components.
μ Hya (23 Hya)3.81244K4 III+40.8Red giant in the lower body; stable.
θ Hya (25 Hya)3.88121B9.5 V-10.7White main-sequence star near μ; variable with white dwarf companion.
ι Hya (27 Hya)3.91253K2.5 III+24.2Orange giant (traditional name Ukdah); marks tail region.
Radial velocities indicate motion relative to the Sun, derived from high-resolution , with positive values denoting recession. These stars' luminosities, typically 20-100 times solar, make them prominent despite moderate apparent brightness, enhancing Hydra's visibility as the largest constellation.

Notable Stellar Phenomena

Variable Stars

Hydra hosts a variety of pulsating variable stars, primarily long-period giants on the (AGB) that exhibit intrinsic brightness changes due to radial pulsations driven by shell flashes or thermal pulses in their envelopes. These stars provide insights into late-stage , where mass loss and pulsation mechanisms lead to observable variations, often monitored by organizations like the American Association of Variable Star Observers (AAVSO). Notable examples include Mira-type variables with large amplitudes and semiregular variables with more irregular but periodic behaviors. R Hydrae, the prototype in Hydra, exemplifies long-period pulsators with a well-documented history of observation. Discovered as variable by Giacomo Maraldi in 1704 after earlier notes by in 1662, it undergoes radial pulsations as an AGB , with its envelope contracting and expanding due to thermal pulses that alter and . Its shows a roughly sinusoidal variation over a mean period of 389 days, though the period has declined from about 495 days in the early 1700s to 380–395 days in recent decades at a rate of 0.58 days per year, possibly linked to a recent thermal pulse around 1770. AAVSO visual observations indicate maximum magnitudes of 3.0 to 6.0 and minima of 9.0 to 11.0, yielding a typical of 6–7 magnitudes; the star's spectroscopic class is M6e–M8e, featuring strong (TiO) bands indicative of its cool, oxygen-rich atmosphere. Semiregular variables in Hydra, such as U Hydrae, represent evolved s with less regular pulsations but still tied to AGB evolution, where carbon from internal shell burning enriches the atmosphere. U Hydrae, a ( type C6.5), displays semiregular variations of subtype SRb with a primary period of approximately 450 days and a small of 0.5 magnitudes, ranging from visual magnitude 4.7 to 5.2. Its is irregular, with occasional cycles around 115 days superimposed, reflecting multiple pulsation modes in its extended , and it emits strong molecular lines like CN and C2 in spectra, highlighting carbon dominance over oxygen. Another prominent example is V Hydrae, a semiregular variable sometimes classified as Mira-like due to its pulsation characteristics and carbon-rich composition. As a (spectral type N6e or C5–C7), it pulsates with a dominant period of 530 days, showing variations with amplitudes up to 2–3 magnitudes, typically ranging from 6.0 to 8.5 in visual observations by AAVSO contributors. Its pulsation mechanism involves radial expansions in the AGB phase, with spectroscopic evidence of elements and dust formation in the , contributing to its deep red color and evolutionary mass loss.
Star NameTypePeriod (days)Magnitude Range (V)Key Feature
R HydraeMira3893.5–10.9Declining period due to thermal pulse; M-type spectrum
U HydraeSemiregular (SRb)~4504.7–5.2 with irregular multi-mode pulsations
V HydraeSemiregular (SRa)/Mira-like5306.0–8.5Strong carbon lines; symbiotic activity possible
These variables' light curves, derived from extensive AAVSO photometric , reveal evolutionary transitions on the AGB, where pulsations drive mass ejection and eventual formation, offering benchmarks for modeling stellar interiors.

Multiple and Binary Systems

Hydra hosts several gravitationally bound multiple and systems, providing valuable insights into and dynamics through their orbital characteristics. Visual binaries in the constellation, such as ε Hydrae, allow direct of relative motions, while spectroscopic and eclipsing systems offer complementary on radial velocities and variations. These systems are cataloged primarily in the Washington Double Star Catalog (WDS), which compiles astrometric measurements to derive like semi-major axes, eccentricities, and periods. Common among components often confirms physical association, distinguishing true multiples from optical alignments. A prominent example is ε Hydrae, a hierarchical multiple system consisting of at least five components. The inner AB pair forms a visual binary with an of 15.07 years and a semi-major axis of 0.252 arcseconds, corresponding to a physical separation of approximately 10 AU at the system's distance of 135 light-years. from indicate a low eccentricity of 0.11, with the primary (ε Hya A, spectral type G6 III, magnitude 3.4) and secondary (ε Hya B, A0 V, magnitude 3.4) exhibiting nearly equal masses around 2.5 M_⊙ each, suggesting co-eval from a common progenitor. The wider C component orbits the AB pair with a period exceeding 890 years and a separation of 4.54 arcseconds, while C itself is a close spectroscopic binary with a 3.41-day period, demonstrating the layered structure typical of such systems. These parameters, derived from combined visual and data, highlight how multiple interactions influence stellar atmospheres and . Spectroscopic binaries in Hydra, detected via Doppler shifts in lines, include λ Hydrae, a double-lined system where both components' curves are observable. Classified as K0 III, the primary shows velocity amplitudes of approximately 5-10 km/s, indicative of a long-period with a semi-major axis of 16.79 mas and period of 1585.8 days (about 4.34 years). The eccentricity is moderate at 0.3, and the mass function suggests a secondary of similar type, with total near 1:1 based on line broadening analysis. Common of 0.23 arcseconds per year confirms the pair's physical binding at 109 light-years distance, supporting models of binary formation in the same . This system's , obtained from high-resolution spectroscopy, imply minimal tidal distortion due to the wide separation, preserving individual evolutionary paths. Eclipsing binaries provide geometric constraints on orbits through photometric minima, as seen in χ² Hydrae, a detached system with an of 2.27 days and near-circular eccentricity of 0.00. The B3 V primary and secondary depths yield a magnitude variation of about 0.4 in V-band, corresponding to radii ratios and inclinations near 90 degrees. amplitudes from spectra give K_A = 120 km/s and K_B = 110 km/s, yielding individual masses of 8.5 M_⊙ and 7.2 M_⊙, respectively, with a separation of 12 R_⊙. These parameters underscore the system's youth and rapid rotation, influencing future phases. Orbital solutions from combined photometry and reveal no significant , affirming stability over evolutionary timescales.
SystemTypePeriod (years)Semi-major Axis (arcsec)EccentricityNotes
ε Hya ABVisual15.070.2520.11Hierarchical multiple; masses ~2.5 M_⊙ each
λ HyaSpectroscopic (SB2)4.340.0170.3Double-lined; common confirmed
χ² HyaEclipsing0.0062 (2.27 days)N/A (photometric)0.00Detached; Δm_V ≈ 0.4; masses 8.5/7.2 M_⊙

Observational Data and Modern Studies

Spectral Types and Distances

The stellar population within the boundaries of the Hydra constellation, as classified in the Henry Draper (HD) catalog and refined through subsequent spectroscopic surveys, includes a notable presence of evolved giant stars in the K and M spectral classes alongside main-sequence dwarfs of earlier types such as A and B. The constellation's extension to higher galactic latitudes (up to b ≈ 50° in parts) contributes to the relative scarcity of hot, young O and B stars compared to regions near the galactic plane. Distance measurements for Hydra's stars, derived from Gaia DR3 parallaxes (released in 2022), indicate that many brighter members (magnitude <4.0) are located within a few hundred light-years of the Sun, with the overall population extending farther for field stars. For more distant associations, such as the open cluster Messier 48 within Hydra's bounds, distances are estimated at around 1,400 light-years based on geometric and photogeometric methods incorporating parallax data. These parallax-based distances highlight Hydra's stars as primarily local disk members. On the Hertzsprung-Russell (HR) diagram, many stars in Hydra occupy the giant branch, particularly in the K and G luminosity classes (III and brighter), indicative of an older population, while the fewer A and B main-sequence representatives (V class) suggest sporadic recent formation. Metallicity trends among these stars generally align with solar-neighborhood values. This placement reflects a mixed-age field without significant substructure, distinguishing Hydra from denser, younger regions.

Recent Discoveries and Exoplanets

The European Space Agency's mission has significantly advanced the study of stars in Hydra through its data releases in the 2020s, providing refined parallaxes and s that have improved distance estimates for more than 100 principal stars in the constellation, addressing uncertainties in earlier measurements. The third data release (DR3) in June 2022 included astrometric data for over 1.8 billion sources across the sky, enabling the identification of new proper motion clusters and associations potentially linked to dynamical structures in the , such as moving groups involving Hydra stars. These updates have revealed kinematic subgroups among fainter members, highlighting Hydra's role in tracing Galactic streams and clusters previously undetected. Post-2000 observations have uncovered several exoplanets and substellar companions orbiting Hydra stars, expanding knowledge beyond traditional catalogs. A key example is the discovery of a brown dwarf companion to υ¹ Hydrae (also known as Zhang), a G7 giant star, detected via high-precision radial velocity measurements from the Okayama Planet Search program; the companion, υ¹ Hydrae b, has a minimum mass of about 54 Jupiter masses and orbits at roughly 13 AU with a period of around 23 years. More recently, the Transiting Exoplanet Survey Satellite (TESS), launched in 2018, identified the GJ 357 system in 2019, featuring three small planets around an M2.5 dwarf star 31 light-years away: GJ 357 b (an Earth-sized transiting hot Earth at 0.323 AU), GJ 357 c (a super-Earth), and GJ 357 d (a potentially habitable super-Earth in the circumstellar habitable zone at 0.545 AU), confirmed through TESS photometry and ground-based radial velocities. Another TESS highlight is the four-planet system around TOI-1203, a G3 V star, reported in 2025, including a warm sub-Neptune (TOI-1203 d) and outer gas giants, validated via intensive radial velocity follow-up. TESS has also flagged numerous TOI candidates in Hydra since 2018, including potential variables and among transiting objects, such as low-mass companions in systems like TOI-4462, contributing to the detection of eclipsing binaries and short-period variables not cataloged in earlier surveys. Additionally, WASP-166 b, a bloated hot super-Neptune (0.1 , radius 0.63 radii) orbiting an F9 V star every 5.4 days, was discovered in 2019 through the () radial velocity survey and confirmed with transits, offering insights into in close-in Neptunes. These findings underscore gaps in pre-2000 catalogs, which lack Gaia-updated distances (now accurate to ~20% for bright Hydra stars) and comprehensive exoplanet inventories; the Exoplanet Archive lists confirmed and candidate planets in Hydra as of November 2025, emphasizing the need for integrated modern datasets.

References

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