Unukalhai, the brightest star in Serpens

Serpens the Serpent is unique in the sky because it’s the only constellation that appears to split in two. The Serpent is being carried by Ophiuchus the Serpent Bearer, and appears both to the east of Ophiuchus as Serpens Cauda the Serpent’s Tail, and to the west as Serpens Caput the Serpent’s Head.

Both parts are made up of largely faint stars but Serpens Caput is easier to identify because of a distinctive zig-zag pattern of stars, the brightest of which is Unukalhai (Alpha (a) Serpentis). Visually, Unukalhai is the brightest star in Serpens and lies in a barren area of sky to the west of the body of Ophiuchus. The star is a good star-hopping aid for locating the zig-zag neck of the serpent leading north toward a less well-defined triangular head.

Unukalhai shines at mag. +2.6 and has a definite orange hue. Its spectrum is K2 III, the ‘III’ indicating it’s a giant star. At its current stage of life, Unukalhai has all but exhausted its core reserve of hydrogen and is now starting to fuse helium into heavier elements such as carbon and oxygen.

Unukalhai’s distance from Earth is estimated at 74 lightyears. Through a scope it has two stars that appear to lie close to it, a mag. +11.8 star 58 arcseconds away and a 13th magnitude star 2.3 arcminutes away. The name Unukalhai means ‘serpent’s neck’, an

5. The Iris Nebula

Go back to Errai and extend a line through the sapphire blue Alfirk (Beta (β) Cephei) a further 3° to a mag. +6.8 star. Half a degree west of this star is a fainter one. Centre this star and use averted vision: surrounding the star you should begin to notice a faint glow a few arcminutes across. This is the Iris Nebula, a reflection nebula that’s lit by the star.  SEEN IT 15x 70

6. UX Draconis

Use the chart to identify 59 Draconis and when you have it centred, look 0.75° back towards Cepheus where there is a very red star. This is UX Draconis, which varies irregularly by up to a magnitude (from mag. +5.9 to +7.1) with a period of around six months. However, we are visiting it for the colour: the carbon in its atmosphere makes it one of the reddest stars anywhere in the night sky.  SEEN IT 10x 50

✓

Tick the box when you’ve seen each one