Editing Canopus (section)

==Physical characteristics==
[[File:Canopus.png|thumb|240x240px|Artistical representation of Canopus. The white color is due to the star having a higher temperature than the [[Sun]].]]
The [[absorption line]]s in the spectrum of Canopus shift slightly with a period of {{val|6.9|u=days}}.  This was first detected in 1906 and the [[doppler effect|Doppler]] variations were interpreted as orbital motion.<ref name=curtis1907>{{cite journal |bibcode=1907PASP...19R.259C |title=The orbits of the spectroscopic binaries alpha Carinae, kappa Velorum, and alpha Pavonis |last1=Curtis |first1=H. D. |journal=Publications of the Astronomical Society of the Pacific |year=1907 |volume=19 |page=259 |doi=10.1086/121781 }}</ref>  An orbit was even calculated, but no such companion exists and the small radial velocity changes are due to movements in the atmosphere of the star.  The maximum observed [[radial velocities]] are only 0.7 to {{val|1.6|ul=km/s}}.  Canopus also has a magnetic field that varies with the same period, detected by the [[Zeeman splitting]] of its spectral lines.<ref name=weiss1986>{{cite journal |bibcode=1986A&A...160..243W | title=The magnetic field of Canopus | last=Weiss | first=W. W. | journal= Astronomy and Astrophysics |volume= 160|pages= 243–250 | year=1986}}</ref>  Canopus is bright at [[microwave]] wavelengths, one of the few F-class stars to be detected by radio.<ref name=gudel2002>{{cite journal |bibcode=2002ARA&A..40..217G |title=Stellar Radio Astronomy: Probing Stellar Atmospheres from Protostars to Giants |last1=Güdel |first1=Manuel |journal=Annual Review of Astronomy and Astrophysics |year=2002 |volume=40 |pages=217–261 |doi=10.1146/annurev.astro.40.060401.093806 |arxiv=astro-ph/0206436 |s2cid=53633983 }}</ref> The [[rotation period]] of the star is not accurately known, but may be over three hundred days.<ref name=Testa2004>{{cite journal | title=The Density of Coronal Plasma in Active Stellar Coronae | last1=Testa | first1=Paola | last2=Drake | first2=Jeremy J. | last3=Peres | first3=Giovanni | journal=The Astrophysical Journal | volume=617 | issue=1 | pages=508–530 | date=December 2004 | doi=10.1086/422355 | arxiv=astro-ph/0405019 | bibcode=2004ApJ...617..508T | s2cid=17532089 }}</ref> The [[projected rotational velocity]] has been measured at 9&nbsp;km/s.<ref name=ayres2018/>

An early [[Interferometry|interferometric]] measurement of its [[angular diameter]] in 1968 gave a [[Limb darkening|limb-darkened]] value of {{val|6.86|ul=mas}}, close to the accepted modern value.<ref>{{cite journal |bibcode=1968ARA&A...6...13B |title=Measurement of Stellar Diameters |last1=Brown |first1=R. Hanbury |journal=Annual Review of Astronomy and Astrophysics |year=1968 |volume=6 |page=13 |doi=10.1146/annurev.aa.06.090168.000305 }}</ref>  [[Very-long-baseline interferometry]] has been used to calculate Canopus' angular diameter at {{val|6.9|ul=mas}}. Combined with distance calculated from its Hipparcos parallax, this gives it a radius of 71 times [[Solar radius|that of the Sun]].<ref name=vlti/> If it were at the centre of the Solar System, it would extend 90% of the way to the orbit of [[Mercury (planet)|Mercury]].<ref name=Kalerstars>{{cite web|url=http://stars.astro.illinois.edu/sow/canopus.html|title=Canopus|last=Kaler|first=Jim|work=Stars|publisher=University of Illinois|access-date=8 July 2012|date=26 June 2009}}</ref> The radius and temperature relative to the Sun means that it is 10,700 times more luminous than the Sun, and its position in the [[H-R diagram]] relative to theoretical [[stellar evolution|evolutionary]] tracks means that it is {{Val|8.0|0.3}} times as massive as the Sun.<ref name=vlti/>  Measurements of its shape find a 1.1° departure from spherical symmetry.<ref name=cruzalebes2015>{{cite journal |bibcode=2015MNRAS.446.3277C |title=Departure from centrosymmetry of red giants and supergiants measured with VLTI/AMBER |last1=Cruzalèbes |first1=P. |last2=Jorissen |first2=A. |last3=Chiavassa |first3=A. |last4=Paladini |first4=C. |last5=Rabbia |first5=Y. |last6=Spang |first6=A. |journal=Monthly Notices of the Royal Astronomical Society |year=2015 |volume=446 |issue=4 |page=3277 |doi=10.1093/mnras/stu2382 |doi-access=free }}</ref>

Canopus is a source of [[X-ray astronomy|X-rays]], which are probably produced by its corona, magnetically heated to several million [[Kelvin]]. The temperature has likely been stimulated by fast rotation combined with strong convection percolating through the star's outer layers.<ref name=ness>{{cite journal|bibcode=2004A&A...427..667N|title=On the sizes of stellar X-ray coronae|journal=Astronomy and Astrophysics|volume=427|issue=2|pages=667–683|last1=Ness|first1=J.-U.|last2=Güdel|first2=M.|last3=Schmitt|first3=J. H. M. M.|last4=Audard|first4=M.|last5=Telleschi|first5=A.|year=2004|doi=10.1051/0004-6361:20040504|arxiv = astro-ph/0407231 |s2cid=11468731}}</ref>  The soft X-ray sub-coronal X-ray emission is much weaker than the hard X-ray coronal emission.  The same behaviour has been measured in other F-class supergiants such as [[α Persei]] and is now believed to be a normal property of such stars.<ref name=ayres2018/>