水蛇座：修订间差异

[[File:Johann Bayer - Uraniometria - Southern Birds.jpg|缩略图|左|350px|[[約翰·拜耳]]《[[測天圖]]》局部细节，水蛇座位于右下方]]

荷兰领航员兼探险家[[皮特·德克斯松·科瑟]]（{{lang|en|Pieter Dirkszoon Keyser}}）和[[弗雷德里克·德·豪特曼]]（{{lang|en|Frederick de Houtman}}）曾跟随[[第一次荷兰远征印度尼西亚]]的船队前往[[东印度]]，[[彼得勒斯·普朗修斯]]根据两人观测结果首次划定包括水蛇座在内的十二星座，并于1598年印上35厘米直径天体仪，与[[约道库斯·洪第乌斯]]合作在[[阿姆斯特丹]]率先出版。1603年，德国天体绘图师[[約翰·拜耳]]在《[[測天圖]]》第一个绘出水蛇座。<ref>{{cite web | url = http://www.ianridpath.com/startales/bayer%20southern.htm | title = Johann Bayer's Southern Star Chart | last = Ridpath | first = Ian | publisher = self-published | work = Star Tales | | access-date = 2021-02-06 | | }}</ref><ref>{{cite web | publisher = [[钱德拉X射线天文台|Chandra X-ray Observatory]] | url = https://chandra.harvard.edu/photo/constellations/hydrus.html | | | title = Hydrus (Water Snake) | access-date = 2021-02-06 | }}</ref>德·豪特曼同年将星座划入南天星表，取德语名称“{{lang|de|De Waterslang}}”，意为“水蛇”<ref>{{cite web | url = http://www.ianridpath.com/startales/startales1c.html#houtman | title = Frederick de Houtman's Catalogue | last = Ridpath | first = Ian | | publisher = self-published | work = Star Tales | access-date = 2021-02-28 | | }}</ref>，代表探险期间遇到的蛇类，与神话无关<ref name="ridphydrus">{{cite web | url = http://www.ianridpath.com/startales/hydrus.html | title = Hydrus—the Lesser Water Snake | last = Ridpath | first = Ian | publisher = self-published | work = Star Tales | | | | access-date = 2021-02-06}}</ref>。1756年，法国探险家兼天文学家[[尼可拉·路易·拉卡伊]]在南天[[活动星图]]将水蛇座称为“{{lang|fr|l’Hydre Mâle}}”，意为雄水蛇，与代表雌水蛇的[[长蛇座]]区别。1763年，拉卡伊将法语名称[[拉丁语|拉丁化]]成“{{lang|la|Hydrus}}”。1776年，[[让·尼古拉斯·福汀]]（{{lang|en|Jean Nicolas Fortin}}）在更新[[約翰·佛蘭斯蒂德]]的《天体图集》时沿用法语名称。<ref>{{cite web | url = http://www.ianridpath.com/startales/lacaille.html | title = Lacaille's Southern Planisphere of 1756 | last = Ridpath | first = Ian | publisher = self-published | work = Star Tales | access-date = 2021-02-06 | | | }}</ref>

[[File:Constellation Hydrus.jpg|缩略图|250px|左|水蛇座可用肉眼识别]]

[[附白一]]位于星座东南角<ref name="motz" />，是光谱等级{{lang|en|M2III}}的[[紅巨星]]，离地214光年<ref>{{cite web | publisher = Centre de Données astronomiques de Strasbourg | access-date = 2021-02-06 |url = http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Gamma+hydri&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id |title = Gamma Hydri—Variable Star | work = SIMBAD Astronomical Database}}</ref>，属[[半規則變星]]，亮度在3.26至3.33视星等范围变动，但科学家经过五年多的观察还无法确定脉动周期<ref>{{cite journal | title = Long-term Photometry and Periods for 261 Nearby Pulsating M Giants | last1 = Tabur | first1 = V. | last2 = Bedding | first2 = T. R. | year = 2009 | journal = Monthly Notices of the Royal Astronomical Society | volume = 400 | issue = 4 | pages = 1945–61 | doi = 10.1111/j.1365-2966.2009.15588.x | arxiv = 0908.3228 | bibcode = 2009MNRAS.400.1945T | last3 = Kiss | first3 = L. L. | last4 = Moon | first4 = T. T. | last5 = Szeidl | first5 = B. | last6 = Kjeldsen | first6 = H.}}</ref>。附白一的质量约为太阳1.5至两倍，直径已扩大到太阳约60倍，光度655倍<ref name="kalergamma">{{cite web | url = http://stars.astro.illinois.edu/sow/gammahyi.html | title = Gamma Hydri | last = Kaler | first = Jim | work = Stars | publisher = University of Illinois | access-date = 2021-02-06 | | | }}</ref>。水蛇座VW位于附白一东北方向3°，是[[大熊座SU]]类[[矮新星]]，也是[[白矮星]]与另一颗恒星组成的闭合[[聯星]]系，其中白矮星还在吸收伴侣恒星的物质，形成明亮的[[吸积盘]]。这种联星系经常爆发，超爆发也很常见。联星爆发时亮度变化比较平衡，超爆发的变化幅度很大。<ref name="AAVSOVW">{{cite web | url = https://www.aavso.org/vsots_vwhyi | title = VW Hydri | last = BSJ | | date = 2010-07-19 | | work = AAVSO Website | publisher = American Association of Variable Star Observers | access-date = 2021-02-06 | }}</ref>。水蛇座VW的亮度在地球夜空所有矮新星中名列前茅<ref>{{cite journal | year = 1974 | title = Photometric Study of the Dwarf Nova VW Hydri | journal = Astronomy and Astrophysics | last = Vogt | first = N. | volume = 36 | pages = 369–378 | bibcode = 1974A&A....36..369V}}</ref>，基准亮度14.4视星等，最活跃时增至8.4视星等<ref name="AAVSOVW" />。水蛇座BL也是闭合联星系，由小质量恒星和强磁场白矮星组成，属[[武仙座AM]]型[[激變變星]]，通称[[高偏振星]]，以白矮星113.6分钟的[[自轉周期]]产生[[偏振]]光波，发射[[红外线]]和强烈的软、硬[[X射线]]<ref>{{cite journal | last1 = Middleditch | last2 = Imamura | last3 = Steiman-Cameron | first1 = John | first2 = James N. | first3 = Thomas Y. | year = 1997 | title = Discovery of Quasi-periodic Oscillations in the AM Herculis Object BL Hydri | journal = Astrophysical Journal | volume = 489 | issue = 2 | pages = 912–916 | doi = 10.1086/304834 | bibcode = 1997ApJ...489..912M}}</ref>。

水蛇座有两个著名[[雙星|光学双星]]。水蛇座π可用双筒望远镜观测<ref name="motz" />，距地球约476光年<ref>{{cite web | publisher = Centre de Données astronomiques de Strasbourg | access-date = 2021-02-07 | | title = HR 667 | work = SIMBAD Astronomical Database | url = http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Pi1+hydri&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id | | }}</ref>。其中主星是红巨星，光谱等级{{lang|en|M1III}}，亮度在5.52至5.58范围变化<ref>{{cite web | url = https://www.aavso.org/vsx/index.php?view=detail.top&oid=39391 | title = NSV 767 | publisher = AAVSO | work = International Variable Star Index | date = 2010-01-18 | | | | access-date = 2021-02-07}}</ref>。从星是光谱等级{{lang|en|K2III}}的橙巨星，距地球约488光年，亮度5.7视星等<ref>{{cite web | access-date = 2021-02-07 | title = HR 678 | | work = SIMBAD Astronomical Database | | url = http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Pi2+hydri&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id | publisher = Centre de Données astronomiques de Strasbourg | }}</ref>。水蛇座η也是光学双星，由[[水蛇座η1|水蛇座η¹]]和[[蛇腹四]]组成<ref name="motz" />。水蛇座η¹是光谱等级{{lang|en|B9V}}的蓝白主序星，有可能是变星<ref>{{cite web | access-date = 2021-02-07 | date = 2010-01-04 | url = https://www.aavso.org/vsx/index.php?view=detail.top&oid=16482 | title = Eta1 Hydri | publisher = AAVSO | work = International Variable Star Index | | | }}</ref>，离地700光年出头<ref>{{cite web | work = SIMBAD Astronomical Database | | | title = Eta 1Hydri—Variable Star | | url = http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Eta1+Hyi&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id | publisher = Centre de Données astronomiques de Strasbourg | access-date = 2021-02-07}}</ref>。蛇腹四是光谱等级{{lang|en|G8.5III}}的4.7视星等黄巨星，距地球约218光年<ref>{{cite web | | | publisher = Centre de Données astronomiques de Strasbourg | url = http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Eta2+Hyi&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id | title = HR 570—Star |work = SIMBAD Astronomical Database | access-date = 2021-02-07 | }}</ref>，已经结束主序星演化阶段，开始膨胀和冷却，朝红巨星方向发展。计算结果表明该星存在大部分时间应该都是白色[[A型主序星]]，质量约为太阳两倍。2005年，人类发现蛇腹四拥有6.5倍[[木星]]质量、相距1.93[[天文單位]]的行星[[水蛇座η2b|水蛇座η²b]]，以711天的公转周期运转。<ref>{{cite journal | last1 = Setiawan | first1 = J. | title = A Substellar Companion Around the Intermediate-mass Giant star HD 11977 | journal = [[天文与天体物理学报|Astronomy & Astrophysics]] | year = 2005 | volume = 437 | issue = 2 | pages = L31–L34 | doi = 10.1051/0004-6361:200500133 | last2 = Rodmann | first2 = J. | last3 = Da Silva | first3 = L. | last4 = Hatzes | first4 = A. P. | last5 = Pasquini | first5 = L. | last6 = Von Der Lühe | first6 = O. | last7 = De Medeiros | first7 = J. R. | last8 = Döllinger | first8 = M. P. | last9 = Girardi | first9 = L. | display-authors = 8 | bibcode = 2005A&A...437L..31S | arxiv = astro-ph/0505510}}</ref>

另有三颗恒星拥有行星，其中又以[[類太陽恆星]][[HD 10180]]最有名，除确定存在的七颗行星外还可能有另外两颗，数量超过包括太阳系在内的所有已知星系<ref name="Tuomi">{{cite journal | last = Tuomi | first = Mikko | title = Evidence for 9 planets in the 10180 system | journal = Astronomy & Astrophysics | date = 2012-04 | arxiv = 1204.1254 | doi = 10.1051/0004-6361/201118518 | volume = 543 | pages = A52 | bibcode = 2012A&A...543A..52T}}</ref>。HD 10180离地约127光年<ref name="BBC11070991">{{Cite news | first = Victoria | last = Gill | date = 2010-08-24 | url = https://www.bbc.co.uk/news/science-environment-11070991 | title = Rich exoplanet system discovered | | work = BBC News | access-date = 2021-02-07 | | }}</ref>，亮度7.33视星等<ref>{{Cite web | title = HD 10180—Star | work = SIMBAD | publisher = Centre de Données astronomiques de Strasbourg | url = http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=HD+10180 | access-date = 2021-02-07 | | | }}</ref>。光谱等级{{lang|en|G8V}}的[[格利泽3021]]也是類太陽恆星，离地57光年，亮度6.7视星等<ref>{{Cite web | title = HD 1237—Pre-main sequence Star | publisher = Centre de Données astronomiques de Strasbourg | | access-date = 2021-02-07 | work = SIMBAD | | url = http://simbad.u-strasbg.fr/simbad/sim-id?Ident=GJ+3021&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id | }}</ref>。质量最少达到木星3.3倍的[[巨行星]][[格利泽3021b]]与格利泽3021相隔约0.5天文单位，公转周期133天<ref name="Naef2001">{{cite journal | title = The CORALIE survey for southern extrasolar planets V. 3 new extrasolar planets | last1 = Naef | first1 = D. | last2 = Mayor | first2 = M. | last3 = Pepe | first3 = F. | last4 = Queloz | first4 = D. | last5 = Santos | first5 = N. C. | last6 = Udry | first6 = S. | last7 = Burnet | first7 = M. | journal = Astronomy and Astrophysics | volume = 375 | issue = 1 | pages = 205–218 | year = 2001 | arxiv = astro-ph/0106255 | bibcode = 2001A&A...375..205N | doi = 10.1051/0004-6361:20010841}}</ref>。距格利泽3021约68天文单位还有光谱等级{{lang|en|M4V}}的暗淡红矮星格利泽3021B（上文的格利泽3021b是小写字母）<ref name="Chauvin2007">{{Cite journal | title = Characterization of the Long-period Companions of the Exoplanet Host Stars: HD 196885, HD 1237 and HD 27442 | last1 = Chauvin | first1 = G. | last2 = Lagrange | first2 = A.-M. | last3 = Udry | first3 = S. | last4 = Mayor | first4 = M. | journal = Astronomy and Astrophysics | volume = 475 | issue = 2 | pages = 723–727 | bibcode = 2007A&A...475..723C | doi = 10.1051/0004-6361:20067046 | arxiv = 0710.5918 | year = 2007}}</ref>。[[HD 20003]]是8.37视星等的黄色主序星，光谱等级{{lang|en|G8V}}，距地球约143光年，质量和温度都略低于太阳。HD 20003有两颗卫星，质量分别是地球约12和13.5倍，公转周期分别是不到12天和34天<ref>{{cite arxiv | eprint = 1109.2497 | class = astro-ph.EP | last1 = Brandão | first1 = I. M. | title = The HARPS search for southern extra-solar planets XXXIV. Occurrence, mass distribution and orbital properties of super-Earths and Neptune-mass planets | last2 = Dogan | first2 = G. | last3 = Christensen-Dalsgaard | first3 = J. | last4 = Cunha | first4 = M. S. | last5 = Bedding | first5 = T. R. | last6 = Metcalfe | first6 = T. S. | last7 = Kjeldsen | first7 = H. | last8 = Bruntt | first8 = H. | last9 = Arentoft | first9 = T. | year = 2011}}</ref>。

水蛇座的[[深空天體]]都很暗淡，其中IC 1717是丹麦天文学家[[約翰·路易·埃米爾·德雷耳]]在19世纪下半叶发现，但如今已不知所踪，估计很可能是暗淡的[[彗星]]<ref name="bagnall251-2">{{cite book | last = Bagnall | first = Philip M. | title = The Star Atlas Companion: What You Need to Know about the Constellations | publisher = Springer | location = New York City | year = 2012 | isbn = 978-1-4614-0830-7 | pages = 251–252 | access-date = 2021-02-07 | }}</ref>。[[PGC 6240]]又称白玫瑰系，是距太阳系约3.45亿光年的巨型[[螺旋星系]]，因外围边缘形似玫瑰花瓣得名。PGC 6240包含三个年龄相差甚远的[[球状星团]]，这种情况非常罕见，估计是在与其他星系合并发生[[星暴]]后形成。<ref>{{cite journal | last1 = Maybhate | first1 = Aparna | title = Evidence for Three Subpopulations of Globular Clusters in the Early-Type Poststarburst Shell Galaxy AM | journal = Astronomical Journal | year = 2007 | volume = 134 | series = 1729 | pages = 139–655 | doi = 10.1086/521817 | arxiv = 0707.3133 | bibcode = 2007AJ....134.1729M | first2 = Paul | last3 = Schweizer | first3 = François | last4 = Puzia | first4 = Thomas | last5 = Carter | first5 = David | issue = 5 | last2 = Goudfrooij}}</ref>NGC 1511也是螺旋星系，接近地球观测范围边缘极限，用业余望远镜就能看到<ref name="hartungs" />。

[[大麦哲伦星系]]大部分位于[[劍魚座]]，小部分在水蛇座范围<ref>{{cite book | last1 = Ellyard | first1 = David | last2 = Tirion | first2 = Wil | year = 2008 | title = The Southern Sky Guide | edition = 3rd | orig-year = 1993 | page = 48 | publisher = Cambridge University Press | location = Port Melbourne, Victoria | isbn = 978-0-521-71405-1 | access-date = 2021-02-07 | }}</ref>。[[NGC 1466]]球状星团是大麦哲伦星系外围部分，里面有很多[[天琴座RR型变星]]，亮度11.59视星等，估计已有超过120亿年历史<ref name="westerlund">{{cite book | last = Westerlund | first = Bengt E. | title = The Magellanic Clouds | publisher = Cambridge University Press | location = Cambridge, United Kingdom | year = 1997 | pages = 57 | chapter = The Age Distribution of Cloud Clusters | isbn = 978-0-521-48070-3 | access-date = 2021-02-07 | }}</ref>。6.3视星等的HD 24188和9.0视星等的HD 24115都是NGC 1466前沿附近恒星<ref name="hartungs" />。[[NGC 602]]包含[[發射星雲]]和明亮的[[疏散星团]]，是[[小麦哲伦星系]]东侧边缘的外围部分<ref>{{cite book | title = 1001 Celestial Wonders to See Before You Die: The Best Sky Objects for Star Gazers | first = Michael E. | last = Bakich | publisher = Springer | location = New York City | year = 2010 | isbn = 978-1-4419-1777-5 | access-date = 2021-02-07 | | page = 373}}</ref>，也是[[银河系]]的[[衛星星系]]，但大部分位于相邻的杜鵑座<ref name="cambridge">{{cite book | last1 = Moore | first1 = Patrick | last2 = Tirion | first2 = Wil | title = Cambridge Guide to Stars and Planets | publisher = Cambridge University Press | location = Cambridge, United Kingdom | year = 1997 | access-date = 2021-02-07 | page = 194 | isbn = 978-0-521-58582-8 | }}</ref>。