Editing Caelum (section)

=== Stars ===
{{See also|List of stars in Caelum}}
Caelum is a faint constellation: It has no star brighter than [[apparent magnitude|magnitude]]&nbsp;4 and only two stars brighter than magnitude&nbsp;5.

Lacaille gave six stars [[Bayer designations]], labeling them Alpha (α<sub>&nbsp;</sub>) to Zeta (ζ<sub>&nbsp;</sub>) in 1756, but omitted Epsilon (ε<sub>&nbsp;</sub>) and designated two adjacent stars as Gamma (γ<sub>&nbsp;</sub>). [[Johann Elert Bode|Bode]] extended the designations to Rho (ρ<sub>&nbsp;</sub>) for other stars, but most of these have fallen out of use.<ref name="wagman">{{cite book  | last = Wagman  | first = Morton  | year = 2003  | title = Lost Stars: Lost, Missing, and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas Louis de Lacaille, John Flamsteed, and Sundry Others | publisher = The McDonald & Woodward Publishing Company | location = [[Blacksburg, Virginia|Blacksburg, VA]]  | isbn = 978-0-939923-78-6 |pages=58–59}}</ref> Caelum is too far south for any of its stars to bear [[Flamsteed designation]]s.{{efn|1=Southern constellations such as Caelum have no Flamsteed designations because Flamsteed only catalogued stars that were visible from England,.<ref name="Starnames">{{cite web |last1=Kaler |first1=J. B. |title=Star Names |publisher=[[University of Illinois at Urbana–Champaign]] |access-date=11 May 2014 |url=http://stars.astro.illinois.edu/sow/starname.html}}</ref>|date=14 February 2014}}

[[Image:Constellation Caelum.jpg|thumb|left|300px|The constellation Caelum as it can be seen by the [[naked eye]].|alt=Image of the constellation Caelum, showing the pattern of its stars as seen in the night sky]]
The brightest star, [[Alpha Caeli|(Alpha) α&nbsp;Caeli]], is a [[double star]], containing an [[F-type main-sequence star]] of magnitude&nbsp;4.45 and a [[red dwarf]] of magnitude&nbsp;12.5<sub>&nbsp;</sub>, {{convert|20.17|pc|ly}} from Earth.<ref name="AlphaSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=alf+Cae |title = * Alpha Caeli – Star in double system|publisher = [[SIMBAD]] | access-date = 13 January 2013}}</ref><ref name="Alpha2Simbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=CCDM%20J04406-4152%20B |title = GJ 174.1 B – Flare star|publisher = [[SIMBAD]] | access-date = 13 January 2013}}</ref> [[Beta Caeli|(Beta) β&nbsp;Caeli]], another [[F-type main-sequence star|F-type star]] of magnitude&nbsp;5.05<sub>&nbsp;</sub>, is further away, being located {{convert|28.67|pc|ly}} from Earth. Unlike α, β&nbsp;Caeli is a [[subgiant]] star, slightly evolved from the main sequence.<ref name="BetaSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=bet+Cae |title = LTT 2063 – High proper-motion Star|publisher = [[SIMBAD]] | access-date = 13 January 2013}}</ref> [[Delta Caeli|(Delta) δ&nbsp;Caeli]], also of magnitude&nbsp;5.05<sub>&nbsp;</sub>, is a [[B-type star|B-type]] subgiant and is much farther from Earth, at {{convert|216|pc|ly}}.<ref name="DeltaSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=del+Cae |title = * Delta Caeli – Star|publisher = [[SIMBAD]] | access-date = 13 January 2013}}</ref>

[[Gamma1 Caeli|(Gamma) γ<sup>1</sup>Caeli]] is a [[double star|double-star]] with a [[red giant]] primary of magnitude&nbsp;4.58 and a secondary of magnitude&nbsp;8.1<sub>&nbsp;</sub>. The primary is {{convert|55.59|pc|ly}} from Earth. The two components are difficult to resolve with small amateur telescopes because of their difference in [[visual magnitude]] and their close separation.<ref name="GammaSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=gam+Cae |title = * Gamma Caeli – Star|publisher = [[SIMBAD]] | access-date = 13 January 2013}}</ref> This star system forms an optical double with the unrelated [[X Caeli|X&nbsp;Caeli]] (previously named γ<sup>2</sup>Caeli), a [[Delta Scuti variable]] located {{convert|98.33|pc|ly}} from Earth.<ref name="XSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=X+Cae |title = V* X Caeli – Variable Star of Delta Scuti type|publisher = [[SIMBAD]] | access-date = 13 January 2013}}</ref> These are a class of short-period (six hours at most) pulsating stars that have been used as [[Cosmic distance ladder#Standard candles|standard candles]] and as subjects to study [[astroseismology]].<ref>{{cite web|url=http://www.aavso.org/vsots_delsct|title=Delta Scuti and the Delta Scuti Variables|last=Templeton|first=M. |date=16 July 2010|work=AAVSO Website|publisher=[[American Association of Variable Star Observers]]|access-date=2 February 2014}}</ref> The only other variable star in Caelum visible to the naked eye is [[RV Caeli|RV&nbsp;Caeli]], a [[pulsating variable|pulsating]] red giant of spectral type M1III,<ref name="RVSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=RV+Cae |title = V* RV Caeli – Pulsating variable Star |publisher = [[SIMBAD]] | access-date = 17 January 2013}}</ref> which varies between magnitudes&nbsp;6.44 and 6.56<sub>&nbsp;</sub>.<ref name=AAVSORV>{{cite web|url=http://www.aavso.org/vsx/index.php?view=detail.top&oid=4525 |title=RV Caeli |last1=X. |first1=V. S. |date=25 August 2009|work=AAVSO Website|publisher=American Association of Variable Star Observers|access-date=3 February 2014}}</ref>

Three other stars in Caelum are still occasionally referred to by their Bayer designations, although they are only on the edge of naked-eye visibility. [[Nu Caeli|(Nu) ν&nbsp;Caeli]]<ref name="NuAstrostudio">{{cite web|author=Ashland Astronomy Studio: Where Art and Science Converge|title=Nu Caeli (HIP 22488)|url=http://www.astrostudio.org/xhip.php?hip=22488|access-date=15 January 2014|url-status=dead|archive-url=https://web.archive.org/web/20140129110728/http://www.astrostudio.org/xhip.php?hip=22488|archive-date=29 January 2014}}</ref> is another double star, containing a [[white giant]] of magnitude&nbsp;6.07<ref name="NuSimbad">{{cite news |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HD+30985 |title = HR 1557 – Star in double system |publisher = [[SIMBAD]] | access-date = 15 January 2013}}</ref> and a star of magnitude&nbsp;10.66, with unknown spectral type.<ref name="Nu2Simbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=CD-41%20%201593B |title = CD-41 1593B – Star in double system |publisher = [[SIMBAD]] | access-date = 15 January 2013}}</ref> The system is approximately {{convert|52.55|pc|ly}} away.<ref name="NuSimbad"/> [[Lambda Caeli|(Lambda) λ&nbsp;Caeli]],<ref name="LambdaAstrostudio">{{cite web|author=Ashland Astronomy Studio: Where Art and Science Converge|title=Lambda Caeli (HIP 21998)|url=http://www.astrostudio.org/xhip.php?hip=21998|access-date=15 January 2014|url-status=dead|archive-url=https://web.archive.org/web/20140129110726/http://www.astrostudio.org/xhip.php?hip=21998|archive-date=29 January 2014}}</ref> at magnitude&nbsp;6.24, is much redder and farther away, being a red giant around {{convert|227|pc|ly}} from Earth.<ref name="LambdaSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HR+1518 |title = HR 1518 – Star |publisher = [[SIMBAD]] | access-date = 15 January 2013}}</ref> [[Zeta Caeli|(Zeta) ζ&nbsp;Caeli]] is even fainter, being only of magnitude&nbsp;6.36<sub>&nbsp;</sub>. This star, located {{convert|132|pc|ly}} away, is a [[K-type star|K-type]] [[subgiant]] of spectral type K1.<ref name="ZetaSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=zet+Cae |title = Zeta Caeli – Star |publisher = [[SIMBAD]] | access-date = 15 January 2013}}</ref> The other twelve naked-eye stars in Caelum are not referred to by Bode's Bayer designations anymore, including RV&nbsp;Caeli.

[[File:Quasar HE0450-2958.jpg|thumb|right|The [[Seyfert galaxy]] [[HE0450-2958]], an unusual [[active galaxy]] in Caelum|alt=An image of the Seyfert galaxy HE0450-2958, showing the active nucleus]]

One of the nearest stars in Caelum is the [[eclipsing binary]] star [[RR Caeli|RR&nbsp;Caeli]], at a distance of {{convert|20.13|pc|ly}}.<ref name="RRSimbad"/> This star system consists of a dim [[red dwarf]] and a [[white dwarf]].<ref name="Bruch">{{Cite journal | last1 = Bruch | first1 = A. | last2 = Diaz | first2 = M. P. | doi = 10.1086/300471 | title = The Eclipsing Precataclysmic Binary RR Caeli | journal = The Astronomical Journal | volume = 116 | issue = 2 | pages = 908 | year = 1998 |bibcode = 1998AJ....116..908B | doi-access = free }}</ref> Despite its closeness to the Earth, the system's apparent magnitude is only 14.40<ref name="RRSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=RR+Cae |title = V* RR Caeli – Eclipsing binary of Algol type (detached) |publisher = [[SIMBAD]] | access-date = 15 January 2013}}</ref> due to the faintness of its components, and thus it cannot be easily seen with amateur equipment. The system is a [[Post common envelope binary|post-common-envelope binary]] and is losing [[angular momentum]] over time, which will eventually cause [[mass transfer]] from the red dwarf to the white dwarf. In approximately 9–20 billion years, this will cause the system to become a [[cataclysmic variable]].<ref name="Maxted">{{Cite journal | last1 = Maxted | first1 = P. F. L. | last2 = O'Donoghue | first2 = D. | last3 = Morales-Rueda | first3 = L. | last4 = Napiwotzki | first4 = R. | last5 = Smalley | first5 = B. | title = The mass and radius of the M-dwarf in the short-period eclipsing binary RR Caeli | doi = 10.1111/j.1365-2966.2007.11564.x| bibcode= 2007MNRAS.376..919M | arxiv = astro-ph/0702005| journal = Monthly Notices of the Royal Astronomical Society | volume = 376 | issue = 2 | pages = 919–928| year = 2007 | doi-access = free | s2cid = 3569936 }}</ref> In 2012, the system was found to contain a [[giant planet]], and there is evidence for a second substellar body.<ref name="Qian">{{Cite journal | last1 = Qian | first1 = S. B. | last2 = Liu | first2 = L. | last3 = Zhu | first3 = L. Y. | last4 = Dai | first4 = Z. B. | last5 = Fernández Lajús | first5 = E. | last6 = Baume | first6 = G. L. | doi = 10.1111/j.1745-3933.2012.01228.x | title = A circumbinary planet in orbit around the short-period white dwarf eclipsing binary RR Cae | journal = Monthly Notices of the Royal Astronomical Society: Letters | volume = 422 | issue = 1 | pages = L24–L27 | year = 2012 |arxiv = 1201.4205 |bibcode = 2012MNRAS.422L..24Q | s2cid = 119190656 }}</ref> {{As of|2021}}, it is believed two planets orbit RR Caeli.<ref name=Rattanamala2021>{{cite journal|last1=Rattanamala|first1=R.|last2=Awiphan|first2=S.|last3=Komonjinda|first3=S.|last4=Phriksee|first4=A.|last5=Sappankum|first5=P.|last6=A-thano|first6=N.|last7=Chitchak|first7=S.|last8=Rittipruk|first8=P.|last9=Sawangwit|first9=U.|last10=Poshyachinda|first10=S.|last11=Reichart|first11=D. E.|last12=Haislip|first12=J. B.|title=Eclipse timing variations in the WD+dM eclipsing binary RR Cae|arxiv=2109.09397|doi=10.1093/mnras/stad1733|year=2021|journal=[[Monthly Notices of the Royal Astronomical Society]]|issue=4|volume=523|pages=5086–5108|doi-access=free }}</ref>

Another nearby star is [[LHS 1678]], an [[astrometric binary]] located some 65&nbsp;[[light-year]]s away. The primary star is a [[red dwarf]] hosting three close-in exoplanets, all smaller than Earth, the secondary component is a likely [[brown dwarf]].<ref name=silverstein_2024>{{Cite journal |last1=Silverstein |first1=Michele L. |last2=Barclay |first2=Thomas |last3=Schlieder |first3=Joshua E. |last4=Collins |first4=Karen A. |last5=Schwarz |first5=Richard P. |last6=Hord |first6=Benjamin J. |last7=Rowe |first7=Jason F. |last8=Kruse |first8=Ethan |last9=Astudillo-Defru |first9=Nicola |last10=Bonfils |first10=Xavier |last11=Caldwell |first11=Douglas A. |last12=Charbonneau |first12=David |last13=Cloutier |first13=Ryan |last14=Collins |first14=Kevin I. |last15=Daylan |first15=Tansu |date=2024-03-01 |title=Validation of a Third Planet in the LHS 1678 System |journal=The Astronomical Journal |volume=167 |issue=6 |pages=255 |doi=10.3847/1538-3881/ad3040 |doi-access=free |arxiv=2403.00110 |bibcode=2024AJ....167..255S |issn=0004-6256}}</ref> This system is notable as the closest star to Alpha Caeli, just 3.3&nbsp;light-years distant.<ref>{{Cite web |title=★ LHS 1678 |url=https://www.stellarcatalog.com/stars/lhs-1678-a |access-date=2024-03-09 |website=Stellar Catalog |language=en}}</ref> Due to its closeness, α&nbsp;Caeli would shine at magnitude {{Val|-2.01}} from LHS&nbsp;1678,<ref>{{Cite web |title=★ Alpha Caeli |url=https://www.stellarcatalog.com/stars/alpha-caeli-a |access-date=2024-03-09 |website=Stellar Catalog |language=en}}</ref>{{efn|1=Using Alpha Caeli's [[absolute magnitude]] ({{val|-3.03}}) and distance from LHS 1678 (3.4 ly), its apparent magnitude can be calculated.<br />M<sub>abs</sub>&minus;5+5{{•}}log(distance (ly) / 3.26) = M<sub>app</sub>.}} brighter than [[Sirius]] in our sky.