Located within the constellation Perseus lies a star called Algol, also known as the ‘Demon Star’ or ‘The Ghoul’. Visible during the autumn months alongside Cassiopeia and Andromeda in the northeastern sky after 9 PM, this celestial object has long been associated with Greek mythology as the ‘blinking eye’ of the gorgon Medusa. But how can a star actually appear to blink?
Algol is actually a triple-star system, with two of the stars closely orbiting each other. This eclipsing binary configuration causes the system’s combined brightness to fluctuate from a bright magnitude +2.1 to a slightly dimmer +3.4 approximately every three days. Data from NASA’s Transiting Exoplanet Survey Satellite (TESS) mission captures this regular dimming cycle, visually representing Medusa’s legendary ‘blinking eye’.
There are abundant resources available to help you track and calculate the dimming—or minima—of Algol, ranging from interactive charts to data plots. Because Algol has a similar magnitude of brightness, you can easily compare its variations to the nearby star Almach (Gamma Andromedae) in the Andromeda constellation using a small telescope or binoculars.
Between the constellations Eridanus and Orion lies a spooky cosmic silhouette, illuminated by the bright star Rigel. Known as IC 2118 or the Witch Head Nebula, this reflection nebula is located approximately 900 light-years away from Earth. Because reflection nebulae depend on nearby starlight to become visible, they are challenging to observe with the naked eye, especially at great distances. While the Witch Head Nebula is invisible to the naked eye, large-aperture telescopes with low magnification make it easier to spot under dark skies. Astrophotographers can capture this haunting outline within a few hours, depending on equipment and sky conditions. For a final spooky touch, you can also seek out the Witch’s Broom nebula, located in the Western Veil Nebula within the constellation Cygnus.
