Infrared image of the Witch Head Nebula showing billowy green and yellow clouds of gas and dust amid a dark, blue-star-filled sky.
NASA/JPL-Caltech

This October, the Night Sky Holds a Blinking Star and a Witch-Shaped Cloud

  • Updated

This October, the night sky is putting on its own Halloween show. Two eerie sights carry the theme: a star known as the Demon Star that seems to blink, and a distant nebula shaped like a witch’s profile.

The blinking star is Algol, in the constellation Perseus, and this month you can catch it in the northeastern sky after 9 PM alongside Cassiopeia and Andromeda. Old stargazers also called it the Ghoul. In Greek myth it’s the eye of Medusa, the gorgon whose gaze turned people to stone.

It really does seem to blink. Algol is a triple-star system where two of its stars orbit each other, and every 3 days or so one passes in front of the other and dims the whole system from bright to noticeably fainter. What you’re watching is a shadow crossing, right on schedule, like an eye slowly closing and opening again.

Line graph showing TESS magnitude of Algol from November 5–27, 2019, with recurring sharp brightness dips and a labeled period of 2.867 days.
NASA’s TESS satellite recorded this light curve of Algol (β Persei) in November 2019, with each sharp dip marking one star eclipsing the other on a 2.867-day cycle. Credit: NASA/Wikimedia Commons.

The witch-shaped cloud sits far off between Orion and Eridanus. It’s a reflection nebula called the Witch Head, roughly 900 light-years away, its haunting profile lit by the nearby star Rigel. You won’t find it with your eyes alone, and even most telescopes need dark skies and patience, but its silhouette really does look like a face turned toward you across the dark.

Infrared image of the Witch Head Nebula showing green glowing gas and dust clouds against a star-filled black sky.
Billowy green clouds of gas and dust form the Witch Head Nebula in this infrared portrait captured by NASA’s Wide-field Infrared Survey Explorer — a stellar nursery where new stars are actively forming. Credit: NASA/JPL-Caltech.

And a witch is never far from her broom. That one is tucked into the Western Veil Nebula, over in the constellation Cygnus.

Look up this month. The sky keeps its own kind of Halloween, and it has for far longer than we have.