Sidus Ludovicianum

Apr 22, 2026 - 21:20
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Sidus Ludovicianum

← Previous revision Revision as of 15:49, 22 April 2026
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'''Sidus Ludovicianum''', also known as '''HD 116798''', is an 8th-magnitude [[star]] in the [[Asterism (astronomy)|asterism]] of the [[Big Dipper]] in the constellation [[Ursa Major]], halfway between [[Mizar and Alcor|Mizar]] and [[Mizar and Alcor|Alcor]]. A line-of-sight companion with Mizar and Alcor (with a spectral type similar to the latter), it is roughly four times more distant. It has the spectral type A8/F0 III. That spectral class suggests it is a [[giant star]], but [[stellar evolution|evolutionary models]] place it on the [[main sequence]].
'''Sidus Ludovicianum''', also known as '''HD 116798''', is an 8th-magnitude [[star]] in the [[Asterism (astronomy)|asterism]] of the [[Big Dipper]] in the constellation [[Ursa Major]], halfway between [[Mizar and Alcor|Mizar]] and [[Mizar and Alcor|Alcor]]. A line-of-sight companion with Mizar and Alcor (with a spectral type similar to the latter), it is roughly four times more distant. It has the spectral type A8/F0 III. That spectral class suggests it is a [[giant star]], but [[stellar evolution|evolutionary models]] place it on the [[main sequence]].


The star was observed on 2 December 1722 by [[Johann Georg Liebknecht]], who mistook it for a planet and named it after [[Louis V, Landgrave of Hesse-Darmstadt]]. Unknown to Liebknecht, it had been previously observed by [[Benedetto Castelli]] in 1616.{{rp|257}} In different sources the name may be written as "Sidus Ludovicianum", "Sidus Ludoviciana", or "Stella Ludoviciana".
The star was observed on 2 December 1722 by [[Johann Georg Liebknecht]], who mistook it for a planet and named it after [[Louis V, Landgrave of Hesse-Darmstadt]]. Unknown to Liebknecht, it had been previously observed by [[Benedetto Castelli]] in 1616.{{rp|257}} In different sources the name may be written as "Sidus Ludovicianum", "Sidus Ludoviciana", or "Stella Ludoviciana".{{rp|257}} The name ''Stella Ludoviciana'' was officially approved by the [[IAU Working Group on Star Names]] on 17 April 2026.


The star is six times more luminous than the [[Sun]], 1.6 times its radius, and has a [[effective temperature|surface temperature]] of {{val|7,200|fmt=commas|ul=K}}. Spectral classification based on a spectrum taken for radial velocity measurement tentatively determined a spectral and luminosity class of A8/F0III, which would indicate that it has exhausted its core hydrogen and started to evolve away from the [[main sequence]], however [[giant stars]] of this type should be at least ten times more luminous than measured for Sidus Ludovicianum. It shows evidence of [[Gamma Doradus variable|Gamma Doradus pulsations]], and is a likely member of a young [[stellar association]] known as Group-X.
The star is six times more luminous than the [[Sun]], 1.6 times its radius, and has a [[effective temperature|surface temperature]] of {{val|7,200|fmt=commas|ul=K}}. Spectral classification based on a spectrum taken for radial velocity measurement tentatively determined a spectral and luminosity class of A8/F0III, which would indicate that it has exhausted its core hydrogen and started to evolve away from the [[main sequence]], however [[giant stars]] of this type should be at least ten times more luminous than measured for Sidus Ludovicianum. It shows evidence of [[Gamma Doradus variable|Gamma Doradus pulsations]], and is a likely member of a young [[stellar association]] known as Group-X.
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{{cite journal |last1=Newton |first1=Elisabeth R. |last2=Rampalli |first2=Rayna |display-authors=etal |date=September 2022 |title=TESS Hunt for Young and Maturing Exoplanets (THYME). VII. Membership, Rotation, and Lithium in the Young Cluster Group-X and a New Young Exoplanet |journal=[[The Astronomical Journal]] |volume=164 |issue=3 |pages=115 |doi=10.3847/1538-3881/ac8154 |doi-access=free |arxiv=2206.06254 |bibcode=2022AJ....164..115N}}
{{cite journal |last1=Newton |first1=Elisabeth R. |last2=Rampalli |first2=Rayna |display-authors=etal |date=September 2022 |title=TESS Hunt for Young and Maturing Exoplanets (THYME). VII. Membership, Rotation, and Lithium in the Young Cluster Group-X and a New Young Exoplanet |journal=[[The Astronomical Journal]] |volume=164 |issue=3 |pages=115 |doi=10.3847/1538-3881/ac8154 |doi-access=free |arxiv=2206.06254 |bibcode=2022AJ....164..115N}}

{{cite web |title=IAU Catalog of Star Names |url=https://exopla.net/star-names/modern-iau-star-names/ |access-date=20 April 2026}}


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