ϑ Serpentis

Theta Serpentis is a beautiful binary (Struve 2417) of two blue-white stars (although others see yellow and white): 4.6, 4.9; PA 104 and a separation of 22.3".

The star marks the tip of the serpent's tail, and is found three right-ascension hours east of alpha. (That's to say, if alpha is due south of you, it will take another three hours to pass before theta finally moves directly to the south of you.)

It's easier, and much more fun, to follow the serpent's form, from head to tail, finally coming to theta, which is two binocular fields of view northeast of eta Serpentis or a little more than three fields due east of beta Ophiuchi: binoculars.

Northwest of theta is the binary Struve 2375AB: 6.3, 6.7; 120, 2.6".

Two degrees west of Struve 2375 is the large and dispersed cluster of 80 stars known as IC 4756, with a scattering of orange giants and blue stragglers.


With the naked eye you can easily follow the tail from tip down to the base: from theta to the southwest there are three stars at roughly the same apparent distance from each other: eta Serpentis, nu Ophiuchus, and then xi Serpentis, which is accompanied by two more that form a triangle: binoculars.

Click on xi Serpentis on the map to continue.

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1999-2014 by Richard Dibon-Smith.