Editing Sirius (section)

=== Discovery of Sirius B ===
[[File:Sirius A and B Hubble photo.jpg|thumb|right|[[Hubble Space Telescope]] image of Sirius&nbsp;A and Sirius&nbsp;B. The white dwarf can be seen to the lower left. The [[diffraction spikes]] and concentric rings are [[Point spread function|instrumental effects]]. Sirius B is approximately one thousand times fainter than Sirius A.]]

In a letter dated 10&nbsp;August 1844, the German astronomer [[Friedrich Bessel|Friedrich Wilhelm Bessel]] deduced from changes in the proper motion of Sirius that it had an unseen companion.<ref name="Bessel1844"/> On 31 January 1862, American telescope-maker and astronomer [[Alvan Graham Clark]] first observed the faint companion, which is now called Sirius&nbsp;B.<ref name="Flammarion1877" /> This happened during testing of an {{convert|18.5|in|adj=on}} aperture [[great refractor]] telescope for [[Dearborn Observatory]], which was one of the largest refracting telescope lenses in existence at the time, and the largest telescope in the [[United States]].<ref name=craig/> Sirius&nbsp;B's sighting was confirmed on 8&nbsp;March with smaller telescopes.<ref>{{cite book |title=Appletons' annual cyclopaedia and register of important events of the year: 1862 |date=1863 |publisher=D. Appleton & Company |location=New York |page=176 |url=https://archive.org/stream/1862appletonsan02newyuoft#page/n183/mode/1up}}</ref>

The visible star is now sometimes known as Sirius&nbsp;A. Since 1894, some apparent orbital irregularities in the Sirius system have been observed, suggesting a third very small companion star, but this has never been confirmed. The best fit to the data indicates a six-year orbit around Sirius&nbsp;A and a mass of {{Solar mass|0.06}}. This star would be five to ten magnitudes fainter than the white dwarf Sirius&nbsp;B, which would make it difficult to observe.<ref name="Benest1995"/> Observations published in 2008 were unable to detect either a third star or a planet. An apparent "third star" observed in the 1920s is now believed to be a background object.<ref name="BonnetBidaud2008"/>

In 1915, [[Walter Sydney Adams]], using a {{Convert|60|in|m|adj=on}} reflector at [[Mount Wilson Observatory]], observed the [[stellar spectrum|spectrum]] of Sirius&nbsp;B and determined that it was a faint whitish star.<ref name="Adams1915"/> This led astronomers to conclude that it was a white dwarf—the second to be discovered.<ref name="Holberg2005"/> The diameter of Sirius&nbsp;A was first measured by [[Robert Hanbury Brown]] and [[Richard Q. Twiss]] in 1959 at [[Jodrell Bank]] using their stellar [[intensity interferometer]].<ref name="Hanbury1958"/> In 2005, using the [[Hubble Space Telescope]], astronomers determined that Sirius&nbsp;B has nearly the diameter of the Earth, {{convert|12000|km}}, with a mass 102% of the Sun's.<ref name="Barstow2005"/>