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52 AUSTRALIAN SKY & TELESCOPE JULY 2016

SUE FRENCH

S

erpens, the Serpent, is the only one of the

88 modern constellations that’s divided into

separate pieces on the sky. Serpens Caput,

containingthisimmensesnake’shead,istothewest

ofthe‘serpentbearer’(Ophiuchus),whileSerpens

Cauda, the beast’s tail end, coils to his east. In the

June 2015 issue we scanned some of the wonders of

thesnake’shead.Nowlet’sseewhattalesthetailcan

tell about our deep sky.

Thestartingpointforourskytouristhetipof

the serpent’s tail,Theta(θ)Serpentis,adoublestar

alsoknownasAlya.AlyamarksthetopofaU-shaped

asterism. The four stars that compose theU’s sides

are dressed in shades of yellow and gold, but Alya is

arrayed in white. Through my 130-mm refractor at

23 ×, Alya splits into nearly matched components, with

Sliding along the Serpent’s tale

Look to the east of Ophiuchus for more deep sky discoveries.

the companion resting east-southeast of its primary.

To me, each star seems dusted with the merest touch

of pale yellow. The 7.8-magnitude, red-orange star HD

175786 hovers north of theU’s eastern side, adding

another dash of colour to the scene.

Each component of the Alya pair is about 1½ to 2

times the diameter and luminosity of our Sun. They’re

believed to make up a physically bound pair. Author

and astronomer Jim Kaler writes that the stars must

be separated by at least 900 times the Earth-Sun

distance. At that separation, he quips, “residents of a

hypothetical ‘earth’ orbiting either one would see the

other shine in their skies with the brightness of some

16 full Moons, allowing them to easily read their issues

of the Alya Gazetteat night.”

Sweeping 4.5° west-northwest from Alya takes us

AKIRA FUJII

IC 4756

θ

η

ν

η

δ

α

α

κ

SERPENS

CAUDA

SERPENS

CAPUT

OPHIUCHUS

South is up in

this wide-angle

view that shows

Serpens split

into two separate

constellations —

Caput, the head,

and Cauda, the

tail — either side

of Ophiuchus,

itself known

as the ‘serpent

bearer’.

Targets