Seginus (Gamma (γ) Boötis) is one of the stars in the main kite-shaped asterism that defines the core of the constellation Boötes the Herdsman
More specifically, it’s the star that marks the westernmost shoulder of the kite, nearest to the Plough.
Shining at mag. +3.0, Seginus has a 12th-magnitude companion 33.4 arcseconds away.
Appearances are deceptive though, as it’s simply a line-of-sight pairing.
Seginus, the bright star, is around 85 lightyears away while the ‘companion’ is estimated at 1,996 lightyears – quite a difference.
Having said this, Seginus isn’t alone, having a true companion just 0.07 arcseconds away.
This translates to 1.8 AU or a bit further than the distance of Mars from the Sun. Little is known about it.
The name Seginus is a corruption of the original Greek name, which meant Boötes.
It’s a giant star of spectral classification A7 IV+(n) or A7 III.
‘IV’ indicates a subgiant, III a normal giant.
The ‘+(n)’ designation indicates that it has broad absorption lines in its spectrum, a result of Seginus’s rapid 139km/s spin.
Despite its giant status, compared to most stars we discuss in this section, Seginus’s size and luminosity are rather modest, being around 5.2 times larger and 33.4 times more luminous than our Sun.
It’s estimated to be around one billion years old.
Seginus is a Delta (δ) Scuti-type variable, varying in brightness between mag. +3.02 and +3.07 over a period of 6.97 hours.
