Binocular Highlight: The Serpent’s Fang

Like a lot of stargazers, I often go observing to escape the hassles of life. Serpens Caput, the head of the celestial snake, is a pretty good getaway spot, with a variety of things to see and do. I like to start with the wide not-quite-a-triangle formed by Beta (β), Gamma (γ), Iota (ι), and Kappa (κ) Serpentis. Most atlases use this group as the “head” of the constellation. That artistic decision is fitting, because the various stars of Tau (τ) Serpentis form a fang-shaped asterism 5° long that points west. The chains of stars, culminating in bright Tau1 Serpentis, even curve like a fang.

If the Tau stars form the serpent’s fang, the group of bright stars running southwest from Gamma to Delta (δ) Serpentis can be seen as the curving hood of a cobra as it rears back to strike. The stars of the fang and the hood are not physically related, though. In both cases, they’re a mix of nearby main-sequence stars with a handful of more distant giants, scattered over several hundred light-years along our line of sight. But they make felicitous groups that are fun to trace out with binoculars.

If you like binocular double stars, this is a rich area. Tau2 and Tau4 Serpentis are wide optical doubles that seem to mirror each other across an imaginary line extending southwest from Tau5 Serpentis. Beta Serpentis is another optical double, tighter but still easily split in low-power binoculars. And pop over the border into Hercules to check out the pairing of Kappa and 8 Herculis. Kappa is itself a close (27) pair of orange giants, which contrast nicely with 8 Herculis, a white A-class main-sequence star.


This article originally appeared in print in the June 2017 issue of Sky & Telescope.

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Mathew Wedel

About Mathew Wedel

By day, Matt Wedel teaches gross anatomy at Western University of Health Sciences in Pomona, California. By night, he enjoys stargazing from the San Gabriel Mountains, the Mojave Desert, and the Salton Sea.
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