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{{Infobox globular cluster
| name = [[梅西耶天體|M]] 55
| image = [[File:Messier 55 VISTA.jpg|300px]]
| caption =在人馬座的球狀星團
| credit = ESO/J. Emerson/VISTA
| epoch = [[J2000]]
| class = XI<ref name=hcob849_11/>
| constellation = [[人馬座]]
| ra = {{RA|19|39|59.71}}<ref name=aj140_6_1830/>
| dec = {{DEC|−30|57|53.1}}<ref name=aj140_6_1830/>
| dist_ly = {{Convert|17.6|kly|kpc|abbr=on|lk=on}}<ref name=apj742_1_51/>
| dist_pc =
| appmag_v = +7.42<ref name="simbad" />
| size_v = 19′.0
| mass_msol = {{Val|2.69|e=5}}<ref name=apj742_1_51/>
| radius_ly = 48 ly<ref>From [[trigonometry]]: radius = {{nowrap|distance × sin( diameter_angle / 2 )}} = {{nowrap|17,600 × sin(19′/2)}} = 48.6 ly.</ref>
| metal_fe = –1.94<ref name=apj742_1_51/>
| v_hb =
| age = 12.3 [[Gigayear|Gyr]]<ref name=aaa481_3_701/>
| notes =
| names = M55, [[New General Catalogue|NGC]] 6809, GCl 113, C 1936-310<ref name="simbad" />
}}

'''梅西耶55''' (也稱為'''M55'''或'''[[NGC天體|NGC]] 6809''')是在南半球[[人馬座]]的[[球狀星團]]。它是由法國天文學家[[尼可拉·路易·拉卡伊]]在南非觀測時，於1752年 6月16日發現的<ref name=thompson2007/>。[[查爾斯·梅西耶|梅西耶]]從1754年開始，就曾多次嘗試在[[巴黎]]找到這個天體，就因為它的緯度太偏南，出現在地平線上的時間很短，妨礙了觀測{{efn|特別是因為它在[[人馬座]]的南部，這使得它在[[北緯50度線]]附近的任何地方雖然仍然都能看見。然而，在整個12月太陽都會經過人馬座（或者嚴格地說是地球繞著太陽在軌道上運行，而使太陽看起來是這樣的）。這也使得在這前後的幾個月裏，星團主要在白天上升，而不是在晚上。}}，使他在1778年才觀測到而將它篇入目錄中。這個星團使用50mm的雙筒望遠鏡就能看到，但要解析出其中的恆星，還需要一架中等大小的望遠鏡<ref name=thompson2007/>。

M55距離[[地球]]大約17,600[[光年]]，擁有的質量大約是269,000[[太陽質量]]({{solar mass}})<ref name=apj742_1_51/>。與銀河系中的其它球狀星團一樣，其中的[[恆星]]都是低[[金屬量]]，即與太陽相比，它除了氫和氦之外幾乎沒有其它元素。金屬量通常是以10為基數的[[對數]]來與太陽比較；對於M55，金屬量的值如下：[Fe/H] = -1.94，而-2的含量將比太陽少100倍<ref name=apj742_1_51/>。這意味著與氫和氦相比，星團的鐵含量僅為太陽的1.1%

在M55的核心部分只發現了大約55顆[[變星]] <ref name=aa60_3_245/>。

== 圖集 ==
{{Gallery|width=200
|File:M55HunterWilson.jpg|使用業餘望遠鏡拍攝的M 55。
|File:M55map.png|標示出M55所在位置的星圖。
}}

== 相關條目 ==
* [[梅西耶天体]]
* [[深空天体]]
* [[人马座]]
* [[NGC天体列表]]

== 參考資料和註解 ==
{{reflist|refs=

<ref name="simbad">{{cite simbad | title=M 55 | access-date=2006-11-16 }}</ref>

<ref name=apj742_1_51>{{citation | display-authors=1 | last1=Boyles | first1=J. | last2=Lorimer | first2=D. R. | last3=Turk | first3=P. J. | last4=Mnatsakanov | first4=R. | last5=Lynch | first5=R. S. | last6=Ransom | first6=S. M. | last7=Freire | first7=P. C. | last8=Belczynski | first8=K. | title=Young Radio Pulsars in Galactic Globular Clusters | journal=The Astrophysical Journal | volume=742 | issue=1 | page=51 |date=November 2011 | doi=10.1088/0004-637X/742/1/51 | bibcode=2011ApJ...742...51B |arxiv = 1108.4402 | s2cid=118649860 }}</ref>

<ref name=thompson2007>{{citation | first1=Robert Bruce | last1=Thompson | first2=Barbara Fritchman | last2=Thompson | title=Illustrated guide to astronomical wonders | series=DIY science | publisher=[[O'Reilly Media, Inc.]] | year=2007 | isbn=978-0-596-52685-6 | page=413 | url=https://books.google.com/books?id=ymt9nj_uPhwC&pg=PA413 }}</ref>

<ref name=aj140_6_1830>{{citation | display-authors=1 | last1=Goldsbury | first1=Ryan | last2=Richer | first2=Harvey B. | last3=Anderson | first3=Jay | last4=Dotter | first4=Aaron | last5=Sarajedini | first5=Ata | last6=Woodley | first6=Kristin | title=The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters | journal=The Astronomical Journal | volume=140 | issue=6 | pages=1830–1837 |date=December 2010 | doi=10.1088/0004-6256/140/6/1830 | bibcode=2010AJ....140.1830G |arxiv = 1008.2755 | s2cid=119183070 }}</ref>

<ref name=aa60_3_245>{{citation | display-authors=1 | last1=Kaluzny | first1=J. | last2=Thompson | first2=I. B. | last3=Krzeminski | first3=W. | last4=Zloczewski | first4=K. | title=The Cluster AgeS Experiment (CASE). Variable Stars in the Globular Cluster M55 | journal=Acta Astronomica | volume=60 | issue=3 | pages=245–260 |date=September 2010 | bibcode=2010AcA....60..245K |arxiv = 1011.0831 }}</ref>

<ref name=hcob849_11>{{citation | last1=Shapley | first1=Harlow | last2=Sawyer | first2=Helen B. | title=A Classification of Globular Clusters | journal=Harvard College Observatory Bulletin | volume=849 | issue=849 | pages=11–14 |date=August 1927 | bibcode=1927BHarO.849...11S | postscript=. }}</ref>

<ref name=aaa481_3_701>{{citation | display-authors=1 | last1=Sollima | first1=A. | last2=Lanzoni | first2=B. | last3=Beccari | first3=G. | last4=Ferraro | first4=F. R. | last5=Fusi Pecci | first5=F. | title=The correlation between blue straggler and binary fractions in the core of Galactic globular clusters | journal=Astronomy and Astrophysics | volume=481 | issue=3 | pages=701–704 |date=April 2008 | doi=10.1051/0004-6361:20079082 | bibcode=2008A&A...481..701S |arxiv = 0801.4511 | s2cid=3088769 }}</ref>

}}
{{notelist}}

== 外部連結 ==
{{Commons category|Messier 55}}
* [http://messier.seds.org/m/m055.html Messier 55, SEDS Messier pages] {{Wayback|url=http://messier.seds.org/m/m055.html |date=20150303153427 }}
* [http://gclusters.altervista.org/cluster_4.php?ggc=M+55 Messier 55, Galactic Globular Clusters Database page] {{Wayback|url=http://gclusters.altervista.org/cluster_4.php?ggc=M+55 |date=20110522201945 }}
* {{APOD |date=23 February 2001|title=M55 Color Magnitude Diagram}}
* {{WikiSky}}

{{Sky|19|39|59.40|-|30|57|43.5|17300}}
{{梅西耶天体}}
{{catalogs|M=55|NGC=6809}}
{{Ngc70}}

[[Category:船底–人馬臂]]
[[Category:球狀星團|M 055]]
[[Category:人馬座|M 055]]
[[Category:梅西耶天體|055]]
[[Category:NGC天體|M 055]]
[[Category:1752年發現的天體|17520616]]

M55 - 版本历史

imported>InternetArchiveBot：​补救2个来源，并将0个来源标记为失效。) #IABot (v2.0.8.7

imported>InternetArchiveBot：补救2个来源，并将0个来源标记为失效。) #IABot (v2.0.8.7